Just when you thought that all the speculation bugs were addressed and

solved and the nightmare is complete, here's the next one: speculating after RET instructions and leaking privileged information using the now pretty much classical covert channels. It is called RETBleed and the mitigation effort and controlling functionality has been modelled similar to what already existing mitigations provide. -----BEGIN PGP SIGNATURE----- iQIzBAABCgAdFiEEzv7L6UO9uDPlPSfHEsHwGGHeVUoFAmLKqAgACgkQEsHwGGHe VUoM5w/8CSvwPZ3otkhmu8MrJPtWc7eLDPjYN4qQP+19e+bt094MoozxeeWG2wmp hkDJAYHT2Oik/qDuEdhFgNYwS7XGgbV3Py3B8syO4//5SD5dkOSG+QqFXvXMdFri YsVqqNkjJOWk/YL9Ql5RS/xQewsrr0OqEyWWocuI6XAvfWV4kKvlRSd+6oPqtZEO qYlAHTXElyIrA/gjmxChk1HTt5HZtK3uJLf4twNlUfzw7LYFf3+sw3bdNuiXlyMr WcLXMwGpS0idURwP3mJa7JRuiVBzb4+kt8mWwWqA02FkKV45FRRRFhFUsy667r00 cdZBaWdy+b7dvXeliO3FN/x1bZwIEUxmaNy1iAClph4Ifh0ySPUkxAr8EIER7YBy bstDJEaIqgYg8NIaD4oF1UrG0ZbL0ImuxVaFdhG1hopQsh4IwLSTLgmZYDhfn/0i oSqU0Le+A7QW9s2A2j6qi7BoAbRW+gmBuCgg8f8ECYRkFX1ZF6mkUtnQxYrU7RTq rJWGW9nhwM9nRxwgntZiTjUUJ2HtyXEgYyCNjLFCbEBfeG5QTg7XSGFhqDbgoymH 85vsmSXYxgTgQ/kTW7Fs26tOqnP2h1OtLJZDL8rg49KijLAnISClEgohYW01CWQf ZKMHtz3DM0WBiLvSAmfGifScgSrLB5AjtvFHT0hF+5/okEkinVk= =09fW -----END PGP SIGNATURE----- Merge tag 'x86_bugs_retbleed' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip Pull x86 retbleed fixes from Borislav Petkov: "Just when you thought that all the speculation bugs were addressed and solved and the nightmare is complete, here's the next one: speculating after RET instructions and leaking privileged information using the now pretty much classical covert channels. It is called RETBleed and the mitigation effort and controlling functionality has been modelled similar to what already existing mitigations provide" * tag 'x86_bugs_retbleed' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (54 commits) x86/speculation: Disable RRSBA behavior x86/kexec: Disable RET on kexec x86/bugs: Do not enable IBPB-on-entry when IBPB is not supported x86/entry: Move PUSH_AND_CLEAR_REGS() back into error_entry x86/bugs: Add Cannon lake to RETBleed affected CPU list x86/retbleed: Add fine grained Kconfig knobs x86/cpu/amd: Enumerate BTC_NO x86/common: Stamp out the stepping madness KVM: VMX: Prevent RSB underflow before vmenter x86/speculation: Fill RSB on vmexit for IBRS KVM: VMX: Fix IBRS handling after vmexit KVM: VMX: Prevent guest RSB poisoning attacks with eIBRS KVM: VMX: Convert launched argument to flags KVM: VMX: Flatten __vmx_vcpu_run() objtool: Re-add UNWIND_HINT_{SAVE_RESTORE} x86/speculation: Remove x86_spec_ctrl_mask x86/speculation: Use cached host SPEC_CTRL value for guest entry/exit x86/speculation: Fix SPEC_CTRL write on SMT state change x86/speculation: Fix firmware entry SPEC_CTRL handling x86/speculation: Fix RSB filling with CONFIG_RETPOLINE=n ...
2024-11-11 06:31:49 +00:00 · 2022-07-11 18:15:25 -07:00 · 2022-07-11 18:15:25 -07:00 · ce114c8668
commit ce114c8668
parent 5a29232d87 4ad3278df6
72 changed files with 1863 additions and 394 deletions
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@ -5197,6 +5197,30 @@

 	retain_initrd	[RAM] Keep initrd memory after extraction

+	retbleed=	[X86] Control mitigation of RETBleed (Arbitrary
+			Speculative Code Execution with Return Instructions)
+			vulnerability.
+
+			off          - no mitigation
+			auto         - automatically select a migitation
+			auto,nosmt   - automatically select a mitigation,
+				       disabling SMT if necessary for
+				       the full mitigation (only on Zen1
+				       and older without STIBP).
+			ibpb	     - mitigate short speculation windows on
+				       basic block boundaries too. Safe, highest
+				       perf impact.
+			unret        - force enable untrained return thunks,
+				       only effective on AMD f15h-f17h
+				       based systems.
+			unret,nosmt  - like unret, will disable SMT when STIBP
+			               is not available.
+
+			Selecting 'auto' will choose a mitigation method at run
+			time according to the CPU.
+
+			Not specifying this option is equivalent to retbleed=auto.
+
 	rfkill.default_state=
 		0	"airplane mode".  All wifi, bluetooth, wimax, gps, fm,
 			etc. communication is blocked by default.
@ -5568,6 +5592,7 @@
 			eibrs		  - enhanced IBRS
 			eibrs,retpoline   - enhanced IBRS + Retpolines
 			eibrs,lfence      - enhanced IBRS + LFENCE
+			ibrs		  - use IBRS to protect kernel

 			Not specifying this option is equivalent to
 			spectre_v2=auto.
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@ -462,29 +462,6 @@ config GOLDFISH
 	def_bool y
 	depends on X86_GOLDFISH

-config RETPOLINE
-	bool "Avoid speculative indirect branches in kernel"
-	select OBJTOOL if HAVE_OBJTOOL
-	default y
-	help
-	  Compile kernel with the retpoline compiler options to guard against
-	  kernel-to-user data leaks by avoiding speculative indirect
-	  branches. Requires a compiler with -mindirect-branch=thunk-extern
-	  support for full protection. The kernel may run slower.
-
-config CC_HAS_SLS
-	def_bool $(cc-option,-mharden-sls=all)
-
-config SLS
-	bool "Mitigate Straight-Line-Speculation"
-	depends on CC_HAS_SLS && X86_64
-	select OBJTOOL if HAVE_OBJTOOL
-	default n
-	help
-	  Compile the kernel with straight-line-speculation options to guard
-	  against straight line speculation. The kernel image might be slightly
-	  larger.
-
 config X86_CPU_RESCTRL
 	bool "x86 CPU resource control support"
 	depends on X86 && (CPU_SUP_INTEL || CPU_SUP_AMD)
@ -2453,6 +2430,91 @@ source "kernel/livepatch/Kconfig"

 endmenu

+config CC_HAS_SLS
+	def_bool $(cc-option,-mharden-sls=all)
+
+config CC_HAS_RETURN_THUNK
+	def_bool $(cc-option,-mfunction-return=thunk-extern)
+
+menuconfig SPECULATION_MITIGATIONS
+	bool "Mitigations for speculative execution vulnerabilities"
+	default y
+	help
+	  Say Y here to enable options which enable mitigations for
+	  speculative execution hardware vulnerabilities.
+
+	  If you say N, all mitigations will be disabled. You really
+	  should know what you are doing to say so.
+
+if SPECULATION_MITIGATIONS
+
+config PAGE_TABLE_ISOLATION
+	bool "Remove the kernel mapping in user mode"
+	default y
+	depends on (X86_64 || X86_PAE)
+	help
+	  This feature reduces the number of hardware side channels by
+	  ensuring that the majority of kernel addresses are not mapped
+	  into userspace.
+
+	  See Documentation/x86/pti.rst for more details.
+
+config RETPOLINE
+	bool "Avoid speculative indirect branches in kernel"
+	select OBJTOOL if HAVE_OBJTOOL
+	default y
+	help
+	  Compile kernel with the retpoline compiler options to guard against
+	  kernel-to-user data leaks by avoiding speculative indirect
+	  branches. Requires a compiler with -mindirect-branch=thunk-extern
+	  support for full protection. The kernel may run slower.
+
+config RETHUNK
+	bool "Enable return-thunks"
+	depends on RETPOLINE && CC_HAS_RETURN_THUNK
+	select OBJTOOL if HAVE_OBJTOOL
+	default y
+	help
+	  Compile the kernel with the return-thunks compiler option to guard
+	  against kernel-to-user data leaks by avoiding return speculation.
+	  Requires a compiler with -mfunction-return=thunk-extern
+	  support for full protection. The kernel may run slower.
+
+config CPU_UNRET_ENTRY
+	bool "Enable UNRET on kernel entry"
+	depends on CPU_SUP_AMD && RETHUNK
+	default y
+	help
+	  Compile the kernel with support for the retbleed=unret mitigation.
+
+config CPU_IBPB_ENTRY
+	bool "Enable IBPB on kernel entry"
+	depends on CPU_SUP_AMD
+	default y
+	help
+	  Compile the kernel with support for the retbleed=ibpb mitigation.
+
+config CPU_IBRS_ENTRY
+	bool "Enable IBRS on kernel entry"
+	depends on CPU_SUP_INTEL
+	default y
+	help
+	  Compile the kernel with support for the spectre_v2=ibrs mitigation.
+	  This mitigates both spectre_v2 and retbleed at great cost to
+	  performance.
+
+config SLS
+	bool "Mitigate Straight-Line-Speculation"
+	depends on CC_HAS_SLS && X86_64
+	select OBJTOOL if HAVE_OBJTOOL
+	default n
+	help
+	  Compile the kernel with straight-line-speculation options to guard
+	  against straight line speculation. The kernel image might be slightly
+	  larger.
+
+endif
+
 config ARCH_HAS_ADD_PAGES
 	def_bool y
 	depends on ARCH_ENABLE_MEMORY_HOTPLUG
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@ -21,6 +21,12 @@ ifdef CONFIG_CC_IS_CLANG
 RETPOLINE_CFLAGS	:= -mretpoline-external-thunk
 RETPOLINE_VDSO_CFLAGS	:= -mretpoline
 endif
+
+ifdef CONFIG_RETHUNK
+RETHUNK_CFLAGS		:= -mfunction-return=thunk-extern
+RETPOLINE_CFLAGS	+= $(RETHUNK_CFLAGS)
+endif
+
 export RETPOLINE_CFLAGS
 export RETPOLINE_VDSO_CFLAGS

--- a/arch/x86/entry/Makefile
+++ b/arch/x86/entry/Makefile
@ -11,7 +11,7 @@ CFLAGS_REMOVE_common.o		= $(CC_FLAGS_FTRACE)

 CFLAGS_common.o			+= -fno-stack-protector

-obj-y				:= entry_$(BITS).o thunk_$(BITS).o syscall_$(BITS).o
+obj-y				:= entry.o entry_$(BITS).o thunk_$(BITS).o syscall_$(BITS).o
 obj-y				+= common.o

 obj-y				+= vdso/
--- a/arch/x86/entry/calling.h
+++ b/arch/x86/entry/calling.h
@ -7,6 +7,8 @@
 #include <asm/asm-offsets.h>
 #include <asm/processor-flags.h>
 #include <asm/ptrace-abi.h>
+#include <asm/msr.h>
+#include <asm/nospec-branch.h>

 /*

@ -282,6 +284,66 @@ For 32-bit we have the following conventions - kernel is built with

 #endif

+/*
+ * IBRS kernel mitigation for Spectre_v2.
+ *
+ * Assumes full context is established (PUSH_REGS, CR3 and GS) and it clobbers
+ * the regs it uses (AX, CX, DX). Must be called before the first RET
+ * instruction (NOTE! UNTRAIN_RET includes a RET instruction)
+ *
+ * The optional argument is used to save/restore the current value,
+ * which is used on the paranoid paths.
+ *
+ * Assumes x86_spec_ctrl_{base,current} to have SPEC_CTRL_IBRS set.
+ */
+.macro IBRS_ENTER save_reg
+#ifdef CONFIG_CPU_IBRS_ENTRY
+	ALTERNATIVE "jmp .Lend_\@", "", X86_FEATURE_KERNEL_IBRS
+	movl	$MSR_IA32_SPEC_CTRL, %ecx
+
+.ifnb \save_reg
+	rdmsr
+	shl	$32, %rdx
+	or	%rdx, %rax
+	mov	%rax, \save_reg
+	test	$SPEC_CTRL_IBRS, %eax
+	jz	.Ldo_wrmsr_\@
+	lfence
+	jmp	.Lend_\@
+.Ldo_wrmsr_\@:
+.endif
+
+	movq	PER_CPU_VAR(x86_spec_ctrl_current), %rdx
+	movl	%edx, %eax
+	shr	$32, %rdx
+	wrmsr
+.Lend_\@:
+#endif
+.endm
+
+/*
+ * Similar to IBRS_ENTER, requires KERNEL GS,CR3 and clobbers (AX, CX, DX)
+ * regs. Must be called after the last RET.
+ */
+.macro IBRS_EXIT save_reg
+#ifdef CONFIG_CPU_IBRS_ENTRY
+	ALTERNATIVE "jmp .Lend_\@", "", X86_FEATURE_KERNEL_IBRS
+	movl	$MSR_IA32_SPEC_CTRL, %ecx
+
+.ifnb \save_reg
+	mov	\save_reg, %rdx
+.else
+	movq	PER_CPU_VAR(x86_spec_ctrl_current), %rdx
+	andl	$(~SPEC_CTRL_IBRS), %edx
+.endif
+
+	movl	%edx, %eax
+	shr	$32, %rdx
+	wrmsr
+.Lend_\@:
+#endif
+.endm
+
 /*
 * Mitigate Spectre v1 for conditional swapgs code paths.
 *
--- a/arch/x86/entry/entry.S
+++ b/arch/x86/entry/entry.S
@ -0,0 +1,22 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Common place for both 32- and 64-bit entry routines.
+ */
+
+#include <linux/linkage.h>
+#include <asm/export.h>
+#include <asm/msr-index.h>
+
+.pushsection .noinstr.text, "ax"
+
+SYM_FUNC_START(entry_ibpb)
+	movl	$MSR_IA32_PRED_CMD, %ecx
+	movl	$PRED_CMD_IBPB, %eax
+	xorl	%edx, %edx
+	wrmsr
+	RET
+SYM_FUNC_END(entry_ibpb)
+/* For KVM */
+EXPORT_SYMBOL_GPL(entry_ibpb);
+
+.popsection
--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@ -698,7 +698,6 @@ SYM_CODE_START(__switch_to_asm)
 	movl	%ebx, PER_CPU_VAR(__stack_chk_guard)
 #endif

-#ifdef CONFIG_RETPOLINE
 	/*
 	 * When switching from a shallower to a deeper call stack
 	 * the RSB may either underflow or use entries populated
@ -707,7 +706,6 @@ SYM_CODE_START(__switch_to_asm)
 	 * speculative execution to prevent attack.
 	 */
 	FILL_RETURN_BUFFER %ebx, RSB_CLEAR_LOOPS, X86_FEATURE_RSB_CTXSW
-#endif

 	/* Restore flags or the incoming task to restore AC state. */
 	popfl
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@ -85,7 +85,7 @@
 */

 SYM_CODE_START(entry_SYSCALL_64)
-	UNWIND_HINT_EMPTY
+	UNWIND_HINT_ENTRY
 	ENDBR

 	swapgs
@ -112,6 +112,11 @@ SYM_INNER_LABEL(entry_SYSCALL_64_after_hwframe, SYM_L_GLOBAL)
 	movq	%rsp, %rdi
 	/* Sign extend the lower 32bit as syscall numbers are treated as int */
 	movslq	%eax, %rsi
+
+	/* clobbers %rax, make sure it is after saving the syscall nr */
+	IBRS_ENTER
+	UNTRAIN_RET
+
 	call	do_syscall_64		/* returns with IRQs disabled */

 	/*
@ -191,6 +196,7 @@ SYM_INNER_LABEL(entry_SYSCALL_64_after_hwframe, SYM_L_GLOBAL)
 	 * perf profiles. Nothing jumps here.
 	 */
 syscall_return_via_sysret:
+	IBRS_EXIT
 	POP_REGS pop_rdi=0

 	/*
@ -249,7 +255,6 @@ SYM_FUNC_START(__switch_to_asm)
 	movq	%rbx, PER_CPU_VAR(fixed_percpu_data) + stack_canary_offset
 #endif

-#ifdef CONFIG_RETPOLINE
 	/*
 	 * When switching from a shallower to a deeper call stack
 	 * the RSB may either underflow or use entries populated
@ -258,7 +263,6 @@ SYM_FUNC_START(__switch_to_asm)
 	 * speculative execution to prevent attack.
 	 */
 	FILL_RETURN_BUFFER %r12, RSB_CLEAR_LOOPS, X86_FEATURE_RSB_CTXSW
-#endif

 	/* restore callee-saved registers */
 	popq	%r15
@ -322,13 +326,13 @@ SYM_CODE_END(ret_from_fork)
 #endif
 .endm

-/* Save all registers in pt_regs */
-SYM_CODE_START_LOCAL(push_and_clear_regs)
+SYM_CODE_START_LOCAL(xen_error_entry)
 	UNWIND_HINT_FUNC
 	PUSH_AND_CLEAR_REGS save_ret=1
 	ENCODE_FRAME_POINTER 8
+	UNTRAIN_RET
 	RET
-SYM_CODE_END(push_and_clear_regs)
+SYM_CODE_END(xen_error_entry)

 /**
 * idtentry_body - Macro to emit code calling the C function
@ -337,9 +341,6 @@ SYM_CODE_END(push_and_clear_regs)
 */
 .macro idtentry_body cfunc has_error_code:req

-	call push_and_clear_regs
-	UNWIND_HINT_REGS
-
 	/*
 	 * Call error_entry() and switch to the task stack if from userspace.
 	 *
@ -349,7 +350,7 @@ SYM_CODE_END(push_and_clear_regs)
 	 * switch the CR3.  So it can skip invoking error_entry().
 	 */
 	ALTERNATIVE "call error_entry; movq %rax, %rsp", \
-		"", X86_FEATURE_XENPV
+		    "call xen_error_entry", X86_FEATURE_XENPV

 	ENCODE_FRAME_POINTER
 	UNWIND_HINT_REGS
@ -612,6 +613,7 @@ __irqentry_text_end:

 SYM_CODE_START_LOCAL(common_interrupt_return)
 SYM_INNER_LABEL(swapgs_restore_regs_and_return_to_usermode, SYM_L_GLOBAL)
+	IBRS_EXIT
 #ifdef CONFIG_DEBUG_ENTRY
 	/* Assert that pt_regs indicates user mode. */
 	testb	$3, CS(%rsp)
@ -725,6 +727,7 @@ native_irq_return_ldt:
 	pushq	%rdi				/* Stash user RDI */
 	swapgs					/* to kernel GS */
 	SWITCH_TO_KERNEL_CR3 scratch_reg=%rdi	/* to kernel CR3 */
+	UNTRAIN_RET

 	movq	PER_CPU_VAR(espfix_waddr), %rdi
 	movq	%rax, (0*8)(%rdi)		/* user RAX */
@ -897,6 +900,9 @@ SYM_CODE_END(xen_failsafe_callback)
 *              1 -> no SWAPGS on exit
 *
 *     Y        GSBASE value at entry, must be restored in paranoid_exit
+ *
+ * R14 - old CR3
+ * R15 - old SPEC_CTRL
 */
 SYM_CODE_START_LOCAL(paranoid_entry)
 	UNWIND_HINT_FUNC
@ -940,7 +946,7 @@ SYM_CODE_START_LOCAL(paranoid_entry)
 	 * is needed here.
 	 */
 	SAVE_AND_SET_GSBASE scratch_reg=%rax save_reg=%rbx
-	RET
+	jmp .Lparanoid_gsbase_done

 .Lparanoid_entry_checkgs:
 	/* EBX = 1 -> kernel GSBASE active, no restore required */
@ -959,8 +965,16 @@ SYM_CODE_START_LOCAL(paranoid_entry)
 	xorl	%ebx, %ebx
 	swapgs
 .Lparanoid_kernel_gsbase:
-
 	FENCE_SWAPGS_KERNEL_ENTRY
+.Lparanoid_gsbase_done:
+
+	/*
+	 * Once we have CR3 and %GS setup save and set SPEC_CTRL. Just like
+	 * CR3 above, keep the old value in a callee saved register.
+	 */
+	IBRS_ENTER save_reg=%r15
+	UNTRAIN_RET
+
 	RET
 SYM_CODE_END(paranoid_entry)

@ -982,9 +996,19 @@ SYM_CODE_END(paranoid_entry)
 *              1 -> no SWAPGS on exit
 *
 *     Y        User space GSBASE, must be restored unconditionally
+ *
+ * R14 - old CR3
+ * R15 - old SPEC_CTRL
 */
 SYM_CODE_START_LOCAL(paranoid_exit)
 	UNWIND_HINT_REGS
+
+	/*
+	 * Must restore IBRS state before both CR3 and %GS since we need access
+	 * to the per-CPU x86_spec_ctrl_shadow variable.
+	 */
+	IBRS_EXIT save_reg=%r15
+
 	/*
 	 * The order of operations is important. RESTORE_CR3 requires
 	 * kernel GSBASE.
@ -1017,6 +1041,10 @@ SYM_CODE_END(paranoid_exit)
 */
 SYM_CODE_START_LOCAL(error_entry)
 	UNWIND_HINT_FUNC
+
+	PUSH_AND_CLEAR_REGS save_ret=1
+	ENCODE_FRAME_POINTER 8
+
 	testb	$3, CS+8(%rsp)
 	jz	.Lerror_kernelspace

@ -1028,9 +1056,12 @@ SYM_CODE_START_LOCAL(error_entry)
 	FENCE_SWAPGS_USER_ENTRY
 	/* We have user CR3.  Change to kernel CR3. */
 	SWITCH_TO_KERNEL_CR3 scratch_reg=%rax
+	IBRS_ENTER
+	UNTRAIN_RET

 	leaq	8(%rsp), %rdi			/* arg0 = pt_regs pointer */
 .Lerror_entry_from_usermode_after_swapgs:
+
 	/* Put us onto the real thread stack. */
 	call	sync_regs
 	RET
@ -1065,6 +1096,7 @@ SYM_CODE_START_LOCAL(error_entry)
 .Lerror_entry_done_lfence:
 	FENCE_SWAPGS_KERNEL_ENTRY
 	leaq	8(%rsp), %rax			/* return pt_regs pointer */
+	ANNOTATE_UNRET_END
 	RET

 .Lbstep_iret:
@ -1080,6 +1112,8 @@ SYM_CODE_START_LOCAL(error_entry)
 	swapgs
 	FENCE_SWAPGS_USER_ENTRY
 	SWITCH_TO_KERNEL_CR3 scratch_reg=%rax
+	IBRS_ENTER
+	UNTRAIN_RET

 	/*
 	 * Pretend that the exception came from user mode: set up pt_regs
@ -1185,6 +1219,9 @@ SYM_CODE_START(asm_exc_nmi)
 	PUSH_AND_CLEAR_REGS rdx=(%rdx)
 	ENCODE_FRAME_POINTER

+	IBRS_ENTER
+	UNTRAIN_RET
+
 	/*
 	 * At this point we no longer need to worry about stack damage
 	 * due to nesting -- we're on the normal thread stack and we're
@ -1409,6 +1446,9 @@ end_repeat_nmi:
 	movq	$-1, %rsi
 	call	exc_nmi

+	/* Always restore stashed SPEC_CTRL value (see paranoid_entry) */
+	IBRS_EXIT save_reg=%r15
+
 	/* Always restore stashed CR3 value (see paranoid_entry) */
 	RESTORE_CR3 scratch_reg=%r15 save_reg=%r14

--- a/arch/x86/entry/entry_64_compat.S
+++ b/arch/x86/entry/entry_64_compat.S
@ -4,7 +4,6 @@
 *
 * Copyright 2000-2002 Andi Kleen, SuSE Labs.
 */
-#include "calling.h"
 #include <asm/asm-offsets.h>
 #include <asm/current.h>
 #include <asm/errno.h>
@ -14,9 +13,12 @@
 #include <asm/irqflags.h>
 #include <asm/asm.h>
 #include <asm/smap.h>
+#include <asm/nospec-branch.h>
 #include <linux/linkage.h>
 #include <linux/err.h>

+#include "calling.h"
+
 	.section .entry.text, "ax"

 /*
@ -47,7 +49,7 @@
 * 0(%ebp) arg6
 */
 SYM_CODE_START(entry_SYSENTER_compat)
-	UNWIND_HINT_EMPTY
+	UNWIND_HINT_ENTRY
 	ENDBR
 	/* Interrupts are off on entry. */
 	swapgs
@ -88,6 +90,9 @@ SYM_INNER_LABEL(entry_SYSENTER_compat_after_hwframe, SYM_L_GLOBAL)

 	cld

+	IBRS_ENTER
+	UNTRAIN_RET
+
 	/*
 	 * SYSENTER doesn't filter flags, so we need to clear NT and AC
 	 * ourselves.  To save a few cycles, we can check whether
@ -174,7 +179,7 @@ SYM_CODE_END(entry_SYSENTER_compat)
 * 0(%esp) arg6
 */
 SYM_CODE_START(entry_SYSCALL_compat)
-	UNWIND_HINT_EMPTY
+	UNWIND_HINT_ENTRY
 	ENDBR
 	/* Interrupts are off on entry. */
 	swapgs
@ -203,6 +208,9 @@ SYM_INNER_LABEL(entry_SYSCALL_compat_after_hwframe, SYM_L_GLOBAL)
 	PUSH_AND_CLEAR_REGS rcx=%rbp rax=$-ENOSYS
 	UNWIND_HINT_REGS

+	IBRS_ENTER
+	UNTRAIN_RET
+
 	movq	%rsp, %rdi
 	call	do_fast_syscall_32
 	/* XEN PV guests always use IRET path */
@ -217,6 +225,8 @@ sysret32_from_system_call:
 	 */
 	STACKLEAK_ERASE

+	IBRS_EXIT
+
 	movq	RBX(%rsp), %rbx		/* pt_regs->rbx */
 	movq	RBP(%rsp), %rbp		/* pt_regs->rbp */
 	movq	EFLAGS(%rsp), %r11	/* pt_regs->flags (in r11) */
@ -295,7 +305,7 @@ SYM_CODE_END(entry_SYSCALL_compat)
 * ebp  arg6
 */
 SYM_CODE_START(entry_INT80_compat)
-	UNWIND_HINT_EMPTY
+	UNWIND_HINT_ENTRY
 	ENDBR
 	/*
 	 * Interrupts are off on entry.
@ -337,6 +347,9 @@ SYM_CODE_START(entry_INT80_compat)

 	cld

+	IBRS_ENTER
+	UNTRAIN_RET
+
 	movq	%rsp, %rdi
 	call	do_int80_syscall_32
 	jmp	swapgs_restore_regs_and_return_to_usermode
--- a/arch/x86/entry/vdso/Makefile
+++ b/arch/x86/entry/vdso/Makefile
@ -92,6 +92,7 @@ endif
 endif

 $(vobjs): KBUILD_CFLAGS := $(filter-out $(CC_FLAGS_LTO) $(RANDSTRUCT_CFLAGS) $(GCC_PLUGINS_CFLAGS) $(RETPOLINE_CFLAGS),$(KBUILD_CFLAGS)) $(CFL)
+$(vobjs): KBUILD_AFLAGS += -DBUILD_VDSO

 #
 # vDSO code runs in userspace and -pg doesn't help with profiling anyway.
--- a/arch/x86/entry/vsyscall/vsyscall_emu_64.S
+++ b/arch/x86/entry/vsyscall/vsyscall_emu_64.S
@ -19,17 +19,20 @@ __vsyscall_page:

 	mov $__NR_gettimeofday, %rax
 	syscall
-	RET
+	ret
+	int3

 	.balign 1024, 0xcc
 	mov $__NR_time, %rax
 	syscall
-	RET
+	ret
+	int3

 	.balign 1024, 0xcc
 	mov $__NR_getcpu, %rax
 	syscall
-	RET
+	ret
+	int3

 	.balign 4096, 0xcc

--- a/arch/x86/include/asm/alternative.h
+++ b/arch/x86/include/asm/alternative.h
@ -76,6 +76,7 @@ extern int alternatives_patched;
 extern void alternative_instructions(void);
 extern void apply_alternatives(struct alt_instr *start, struct alt_instr *end);
 extern void apply_retpolines(s32 *start, s32 *end);
+extern void apply_returns(s32 *start, s32 *end);
 extern void apply_ibt_endbr(s32 *start, s32 *end);

 struct module;
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@ -203,8 +203,8 @@
 #define X86_FEATURE_PROC_FEEDBACK	( 7*32+ 9) /* AMD ProcFeedbackInterface */
 #define X86_FEATURE_XCOMPACTED		( 7*32+10) /* "" Use compacted XSTATE (XSAVES or XSAVEC) */
 #define X86_FEATURE_PTI			( 7*32+11) /* Kernel Page Table Isolation enabled */
-#define X86_FEATURE_RETPOLINE		( 7*32+12) /* "" Generic Retpoline mitigation for Spectre variant 2 */
-#define X86_FEATURE_RETPOLINE_LFENCE	( 7*32+13) /* "" Use LFENCE for Spectre variant 2 */
+#define X86_FEATURE_KERNEL_IBRS		( 7*32+12) /* "" Set/clear IBRS on kernel entry/exit */
+#define X86_FEATURE_RSB_VMEXIT		( 7*32+13) /* "" Fill RSB on VM-Exit */
 #define X86_FEATURE_INTEL_PPIN		( 7*32+14) /* Intel Processor Inventory Number */
 #define X86_FEATURE_CDP_L2		( 7*32+15) /* Code and Data Prioritization L2 */
 #define X86_FEATURE_MSR_SPEC_CTRL	( 7*32+16) /* "" MSR SPEC_CTRL is implemented */
@ -296,6 +296,12 @@
 #define X86_FEATURE_PER_THREAD_MBA	(11*32+ 7) /* "" Per-thread Memory Bandwidth Allocation */
 #define X86_FEATURE_SGX1		(11*32+ 8) /* "" Basic SGX */
 #define X86_FEATURE_SGX2		(11*32+ 9) /* "" SGX Enclave Dynamic Memory Management (EDMM) */
+#define X86_FEATURE_ENTRY_IBPB		(11*32+10) /* "" Issue an IBPB on kernel entry */
+#define X86_FEATURE_RRSBA_CTRL		(11*32+11) /* "" RET prediction control */
+#define X86_FEATURE_RETPOLINE		(11*32+12) /* "" Generic Retpoline mitigation for Spectre variant 2 */
+#define X86_FEATURE_RETPOLINE_LFENCE	(11*32+13) /* "" Use LFENCE for Spectre variant 2 */
+#define X86_FEATURE_RETHUNK		(11*32+14) /* "" Use REturn THUNK */
+#define X86_FEATURE_UNRET		(11*32+15) /* "" AMD BTB untrain return */

 /* Intel-defined CPU features, CPUID level 0x00000007:1 (EAX), word 12 */
 #define X86_FEATURE_AVX_VNNI		(12*32+ 4) /* AVX VNNI instructions */
@ -316,6 +322,7 @@
 #define X86_FEATURE_VIRT_SSBD		(13*32+25) /* Virtualized Speculative Store Bypass Disable */
 #define X86_FEATURE_AMD_SSB_NO		(13*32+26) /* "" Speculative Store Bypass is fixed in hardware. */
 #define X86_FEATURE_CPPC		(13*32+27) /* Collaborative Processor Performance Control */
+#define X86_FEATURE_BTC_NO		(13*32+29) /* "" Not vulnerable to Branch Type Confusion */
 #define X86_FEATURE_BRS			(13*32+31) /* Branch Sampling available */

 /* Thermal and Power Management Leaf, CPUID level 0x00000006 (EAX), word 14 */
@ -447,5 +454,6 @@
 #define X86_BUG_ITLB_MULTIHIT		X86_BUG(23) /* CPU may incur MCE during certain page attribute changes */
 #define X86_BUG_SRBDS			X86_BUG(24) /* CPU may leak RNG bits if not mitigated */
 #define X86_BUG_MMIO_STALE_DATA		X86_BUG(25) /* CPU is affected by Processor MMIO Stale Data vulnerabilities */
+#define X86_BUG_RETBLEED		X86_BUG(26) /* CPU is affected by RETBleed */

 #endif /* _ASM_X86_CPUFEATURES_H */
--- a/arch/x86/include/asm/disabled-features.h
+++ b/arch/x86/include/asm/disabled-features.h
@ -50,6 +50,25 @@
 # define DISABLE_PTI		(1 << (X86_FEATURE_PTI & 31))
 #endif

+#ifdef CONFIG_RETPOLINE
+# define DISABLE_RETPOLINE	0
+#else
+# define DISABLE_RETPOLINE	((1 << (X86_FEATURE_RETPOLINE & 31)) | \
+				 (1 << (X86_FEATURE_RETPOLINE_LFENCE & 31)))
+#endif
+
+#ifdef CONFIG_RETHUNK
+# define DISABLE_RETHUNK	0
+#else
+# define DISABLE_RETHUNK	(1 << (X86_FEATURE_RETHUNK & 31))
+#endif
+
+#ifdef CONFIG_CPU_UNRET_ENTRY
+# define DISABLE_UNRET		0
+#else
+# define DISABLE_UNRET		(1 << (X86_FEATURE_UNRET & 31))
+#endif
+
 #ifdef CONFIG_INTEL_IOMMU_SVM
 # define DISABLE_ENQCMD		0
 #else
@ -82,7 +101,7 @@
 #define DISABLED_MASK8	(DISABLE_TDX_GUEST)
 #define DISABLED_MASK9	(DISABLE_SGX)
 #define DISABLED_MASK10	0
-#define DISABLED_MASK11	0
+#define DISABLED_MASK11	(DISABLE_RETPOLINE|DISABLE_RETHUNK|DISABLE_UNRET)
 #define DISABLED_MASK12	0
 #define DISABLED_MASK13	0
 #define DISABLED_MASK14	0
--- a/arch/x86/include/asm/linkage.h
+++ b/arch/x86/include/asm/linkage.h
@ -19,19 +19,27 @@
 #define __ALIGN_STR	__stringify(__ALIGN)
 #endif

+#if defined(CONFIG_RETHUNK) && !defined(__DISABLE_EXPORTS) && !defined(BUILD_VDSO)
+#define RET	jmp __x86_return_thunk
+#else /* CONFIG_RETPOLINE */
 #ifdef CONFIG_SLS
 #define RET	ret; int3
 #else
 #define RET	ret
 #endif
+#endif /* CONFIG_RETPOLINE */

 #else /* __ASSEMBLY__ */

+#if defined(CONFIG_RETHUNK) && !defined(__DISABLE_EXPORTS) && !defined(BUILD_VDSO)
+#define ASM_RET	"jmp __x86_return_thunk\n\t"
+#else /* CONFIG_RETPOLINE */
 #ifdef CONFIG_SLS
 #define ASM_RET	"ret; int3\n\t"
 #else
 #define ASM_RET	"ret\n\t"
 #endif
+#endif /* CONFIG_RETPOLINE */

 #endif /* __ASSEMBLY__ */

--- a/arch/x86/include/asm/msr-index.h
+++ b/arch/x86/include/asm/msr-index.h
@ -51,6 +51,8 @@
 #define SPEC_CTRL_STIBP			BIT(SPEC_CTRL_STIBP_SHIFT)	/* STIBP mask */
 #define SPEC_CTRL_SSBD_SHIFT		2	   /* Speculative Store Bypass Disable bit */
 #define SPEC_CTRL_SSBD			BIT(SPEC_CTRL_SSBD_SHIFT)	/* Speculative Store Bypass Disable */
+#define SPEC_CTRL_RRSBA_DIS_S_SHIFT	6	   /* Disable RRSBA behavior */
+#define SPEC_CTRL_RRSBA_DIS_S		BIT(SPEC_CTRL_RRSBA_DIS_S_SHIFT)

 #define MSR_IA32_PRED_CMD		0x00000049 /* Prediction Command */
 #define PRED_CMD_IBPB			BIT(0)	   /* Indirect Branch Prediction Barrier */
@ -93,6 +95,7 @@
 #define MSR_IA32_ARCH_CAPABILITIES	0x0000010a
 #define ARCH_CAP_RDCL_NO		BIT(0)	/* Not susceptible to Meltdown */
 #define ARCH_CAP_IBRS_ALL		BIT(1)	/* Enhanced IBRS support */
+#define ARCH_CAP_RSBA			BIT(2)	/* RET may use alternative branch predictors */
 #define ARCH_CAP_SKIP_VMENTRY_L1DFLUSH	BIT(3)	/* Skip L1D flush on vmentry */
 #define ARCH_CAP_SSB_NO			BIT(4)	/*
 						 * Not susceptible to Speculative Store Bypass
@ -140,6 +143,13 @@
 						 * bit available to control VERW
 						 * behavior.
 						 */
+#define ARCH_CAP_RRSBA			BIT(19)	/*
+						 * Indicates RET may use predictors
+						 * other than the RSB. With eIBRS
+						 * enabled predictions in kernel mode
+						 * are restricted to targets in
+						 * kernel.
+						 */

 #define MSR_IA32_FLUSH_CMD		0x0000010b
 #define L1D_FLUSH			BIT(0)	/*
@ -567,6 +577,9 @@
 /* Fam 17h MSRs */
 #define MSR_F17H_IRPERF			0xc00000e9

+#define MSR_ZEN2_SPECTRAL_CHICKEN	0xc00110e3
+#define MSR_ZEN2_SPECTRAL_CHICKEN_BIT	BIT_ULL(1)
+
 /* Fam 16h MSRs */
 #define MSR_F16H_L2I_PERF_CTL		0xc0010230
 #define MSR_F16H_L2I_PERF_CTR		0xc0010231
--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@ -75,6 +75,23 @@
 	.popsection
 .endm

+/*
+ * (ab)use RETPOLINE_SAFE on RET to annotate away 'bare' RET instructions
+ * vs RETBleed validation.
+ */
+#define ANNOTATE_UNRET_SAFE ANNOTATE_RETPOLINE_SAFE
+
+/*
+ * Abuse ANNOTATE_RETPOLINE_SAFE on a NOP to indicate UNRET_END, should
+ * eventually turn into it's own annotation.
+ */
+.macro ANNOTATE_UNRET_END
+#ifdef CONFIG_DEBUG_ENTRY
+	ANNOTATE_RETPOLINE_SAFE
+	nop
+#endif
+.endm
+
 /*
 * JMP_NOSPEC and CALL_NOSPEC macros can be used instead of a simple
 * indirect jmp/call which may be susceptible to the Spectre variant 2
@ -105,10 +122,34 @@
  * monstrosity above, manually.
  */
 .macro FILL_RETURN_BUFFER reg:req nr:req ftr:req
-#ifdef CONFIG_RETPOLINE
 	ALTERNATIVE "jmp .Lskip_rsb_\@", "", \ftr
 	__FILL_RETURN_BUFFER(\reg,\nr,%_ASM_SP)
 .Lskip_rsb_\@:
+.endm
+
+#ifdef CONFIG_CPU_UNRET_ENTRY
+#define CALL_ZEN_UNTRAIN_RET	"call zen_untrain_ret"
+#else
+#define CALL_ZEN_UNTRAIN_RET	""
+#endif
+
+/*
+ * Mitigate RETBleed for AMD/Hygon Zen uarch. Requires KERNEL CR3 because the
+ * return thunk isn't mapped into the userspace tables (then again, AMD
+ * typically has NO_MELTDOWN).
+ *
+ * While zen_untrain_ret() doesn't clobber anything but requires stack,
+ * entry_ibpb() will clobber AX, CX, DX.
+ *
+ * As such, this must be placed after every *SWITCH_TO_KERNEL_CR3 at a point
+ * where we have a stack but before any RET instruction.
+ */
+.macro UNTRAIN_RET
+#if defined(CONFIG_CPU_UNRET_ENTRY) || defined(CONFIG_CPU_IBPB_ENTRY)
+	ANNOTATE_UNRET_END
+	ALTERNATIVE_2 "",						\
+	              CALL_ZEN_UNTRAIN_RET, X86_FEATURE_UNRET,		\
+		      "call entry_ibpb", X86_FEATURE_ENTRY_IBPB
 #endif
 .endm

@ -120,17 +161,20 @@
 	_ASM_PTR " 999b\n\t"					\
 	".popsection\n\t"

-#ifdef CONFIG_RETPOLINE
-
 typedef u8 retpoline_thunk_t[RETPOLINE_THUNK_SIZE];
+extern retpoline_thunk_t __x86_indirect_thunk_array[];
+
+extern void __x86_return_thunk(void);
+extern void zen_untrain_ret(void);
+extern void entry_ibpb(void);
+
+#ifdef CONFIG_RETPOLINE

 #define GEN(reg) \
 	extern retpoline_thunk_t __x86_indirect_thunk_ ## reg;
 #include <asm/GEN-for-each-reg.h>
 #undef GEN

-extern retpoline_thunk_t __x86_indirect_thunk_array[];
-
 #ifdef CONFIG_X86_64

 /*
@ -193,6 +237,7 @@ enum spectre_v2_mitigation {
 	SPECTRE_V2_EIBRS,
 	SPECTRE_V2_EIBRS_RETPOLINE,
 	SPECTRE_V2_EIBRS_LFENCE,
+	SPECTRE_V2_IBRS,
 };

 /* The indirect branch speculation control variants */
@ -235,6 +280,9 @@ static inline void indirect_branch_prediction_barrier(void)

 /* The Intel SPEC CTRL MSR base value cache */
 extern u64 x86_spec_ctrl_base;
+extern u64 x86_spec_ctrl_current;
+extern void write_spec_ctrl_current(u64 val, bool force);
+extern u64 spec_ctrl_current(void);

 /*
 * With retpoline, we must use IBRS to restrict branch prediction
@ -244,18 +292,16 @@ extern u64 x86_spec_ctrl_base;
 */
 #define firmware_restrict_branch_speculation_start()			\
 do {									\
-	u64 val = x86_spec_ctrl_base | SPEC_CTRL_IBRS;			\
-									\
 	preempt_disable();						\
-	alternative_msr_write(MSR_IA32_SPEC_CTRL, val,			\
+	alternative_msr_write(MSR_IA32_SPEC_CTRL,			\
+			      spec_ctrl_current() | SPEC_CTRL_IBRS,	\
 			      X86_FEATURE_USE_IBRS_FW);			\
 } while (0)

 #define firmware_restrict_branch_speculation_end()			\
 do {									\
-	u64 val = x86_spec_ctrl_base;					\
-									\
-	alternative_msr_write(MSR_IA32_SPEC_CTRL, val,			\
+	alternative_msr_write(MSR_IA32_SPEC_CTRL,			\
+			      spec_ctrl_current(),			\
 			      X86_FEATURE_USE_IBRS_FW);			\
 	preempt_enable();						\
 } while (0)
--- a/arch/x86/include/asm/static_call.h
+++ b/arch/x86/include/asm/static_call.h
@ -21,6 +21,16 @@
 * relative displacement across sections.
 */

+/*
+ * The trampoline is 8 bytes and of the general form:
+ *
+ *   jmp.d32 \func
+ *   ud1 %esp, %ecx
+ *
+ * That trailing #UD provides both a speculation stop and serves as a unique
+ * 3 byte signature identifying static call trampolines. Also see tramp_ud[]
+ * and __static_call_fixup().
+ */
 #define __ARCH_DEFINE_STATIC_CALL_TRAMP(name, insns)			\
 	asm(".pushsection .static_call.text, \"ax\"		\n"	\
 	    ".align 4						\n"	\
@ -28,7 +38,7 @@
 	    STATIC_CALL_TRAMP_STR(name) ":			\n"	\
 	    ANNOTATE_NOENDBR						\
 	    insns "						\n"	\
-	    ".byte 0x53, 0x43, 0x54				\n"	\
+	    ".byte 0x0f, 0xb9, 0xcc				\n"	\
 	    ".type " STATIC_CALL_TRAMP_STR(name) ", @function	\n"	\
 	    ".size " STATIC_CALL_TRAMP_STR(name) ", . - " STATIC_CALL_TRAMP_STR(name) " \n" \
 	    ".popsection					\n")
@ -36,8 +46,13 @@
 #define ARCH_DEFINE_STATIC_CALL_TRAMP(name, func)			\
 	__ARCH_DEFINE_STATIC_CALL_TRAMP(name, ".byte 0xe9; .long " #func " - (. + 4)")

+#ifdef CONFIG_RETHUNK
+#define ARCH_DEFINE_STATIC_CALL_NULL_TRAMP(name)			\
+	__ARCH_DEFINE_STATIC_CALL_TRAMP(name, "jmp __x86_return_thunk")
+#else
 #define ARCH_DEFINE_STATIC_CALL_NULL_TRAMP(name)			\
 	__ARCH_DEFINE_STATIC_CALL_TRAMP(name, "ret; int3; nop; nop; nop")
+#endif

 #define ARCH_DEFINE_STATIC_CALL_RET0_TRAMP(name)			\
 	ARCH_DEFINE_STATIC_CALL_TRAMP(name, __static_call_return0)
@ -48,4 +63,6 @@
 	    ".long " STATIC_CALL_KEY_STR(name) " - .		\n"	\
 	    ".popsection					\n")

+extern bool __static_call_fixup(void *tramp, u8 op, void *dest);
+
 #endif /* _ASM_STATIC_CALL_H */
--- a/arch/x86/include/asm/unwind_hints.h
+++ b/arch/x86/include/asm/unwind_hints.h
@ -8,7 +8,11 @@
 #ifdef __ASSEMBLY__

 .macro UNWIND_HINT_EMPTY
-	UNWIND_HINT sp_reg=ORC_REG_UNDEFINED type=UNWIND_HINT_TYPE_CALL end=1
+	UNWIND_HINT type=UNWIND_HINT_TYPE_CALL end=1
+.endm
+
+.macro UNWIND_HINT_ENTRY
+	UNWIND_HINT type=UNWIND_HINT_TYPE_ENTRY end=1
 .endm

 .macro UNWIND_HINT_REGS base=%rsp offset=0 indirect=0 extra=1 partial=0
@ -52,6 +56,14 @@
 	UNWIND_HINT sp_reg=ORC_REG_SP sp_offset=8 type=UNWIND_HINT_TYPE_FUNC
 .endm

+.macro UNWIND_HINT_SAVE
+	UNWIND_HINT type=UNWIND_HINT_TYPE_SAVE
+.endm
+
+.macro UNWIND_HINT_RESTORE
+	UNWIND_HINT type=UNWIND_HINT_TYPE_RESTORE
+.endm
+
 #else

 #define UNWIND_HINT_FUNC \
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@ -115,6 +115,7 @@ static void __init_or_module add_nops(void *insns, unsigned int len)
 }

 extern s32 __retpoline_sites[], __retpoline_sites_end[];
+extern s32 __return_sites[], __return_sites_end[];
 extern s32 __ibt_endbr_seal[], __ibt_endbr_seal_end[];
 extern struct alt_instr __alt_instructions[], __alt_instructions_end[];
 extern s32 __smp_locks[], __smp_locks_end[];
@ -507,9 +508,76 @@ void __init_or_module noinline apply_retpolines(s32 *start, s32 *end)
 	}
 }

+#ifdef CONFIG_RETHUNK
+/*
+ * Rewrite the compiler generated return thunk tail-calls.
+ *
+ * For example, convert:
+ *
+ *   JMP __x86_return_thunk
+ *
+ * into:
+ *
+ *   RET
+ */
+static int patch_return(void *addr, struct insn *insn, u8 *bytes)
+{
+	int i = 0;
+
+	if (cpu_feature_enabled(X86_FEATURE_RETHUNK))
+		return -1;
+
+	bytes[i++] = RET_INSN_OPCODE;
+
+	for (; i < insn->length;)
+		bytes[i++] = INT3_INSN_OPCODE;
+
+	return i;
+}
+
+void __init_or_module noinline apply_returns(s32 *start, s32 *end)
+{
+	s32 *s;
+
+	for (s = start; s < end; s++) {
+		void *dest = NULL, *addr = (void *)s + *s;
+		struct insn insn;
+		int len, ret;
+		u8 bytes[16];
+		u8 op;
+
+		ret = insn_decode_kernel(&insn, addr);
+		if (WARN_ON_ONCE(ret < 0))
+			continue;
+
+		op = insn.opcode.bytes[0];
+		if (op == JMP32_INSN_OPCODE)
+			dest = addr + insn.length + insn.immediate.value;
+
+		if (__static_call_fixup(addr, op, dest) ||
+		    WARN_ON_ONCE(dest != &__x86_return_thunk))
+			continue;
+
+		DPRINTK("return thunk at: %pS (%px) len: %d to: %pS",
+			addr, addr, insn.length,
+			addr + insn.length + insn.immediate.value);
+
+		len = patch_return(addr, &insn, bytes);
+		if (len == insn.length) {
+			DUMP_BYTES(((u8*)addr),  len, "%px: orig: ", addr);
+			DUMP_BYTES(((u8*)bytes), len, "%px: repl: ", addr);
+			text_poke_early(addr, bytes, len);
+		}
+	}
+}
+#else
+void __init_or_module noinline apply_returns(s32 *start, s32 *end) { }
+#endif /* CONFIG_RETHUNK */
+
 #else /* !CONFIG_RETPOLINE || !CONFIG_OBJTOOL */

 void __init_or_module noinline apply_retpolines(s32 *start, s32 *end) { }
+void __init_or_module noinline apply_returns(s32 *start, s32 *end) { }

 #endif /* CONFIG_RETPOLINE && CONFIG_OBJTOOL */

@ -860,6 +928,7 @@ void __init alternative_instructions(void)
 	 * those can rewrite the retpoline thunks.
 	 */
 	apply_retpolines(__retpoline_sites, __retpoline_sites_end);
+	apply_returns(__return_sites, __return_sites_end);

 	/*
 	 * Then patch alternatives, such that those paravirt calls that are in
--- a/arch/x86/kernel/asm-offsets.c
+++ b/arch/x86/kernel/asm-offsets.c
@ -19,6 +19,7 @@
 #include <asm/suspend.h>
 #include <asm/tlbflush.h>
 #include <asm/tdx.h>
+#include "../kvm/vmx/vmx.h"

 #ifdef CONFIG_XEN
 #include <xen/interface/xen.h>
@ -107,4 +108,9 @@ static void __used common(void)
 	OFFSET(TSS_sp0, tss_struct, x86_tss.sp0);
 	OFFSET(TSS_sp1, tss_struct, x86_tss.sp1);
 	OFFSET(TSS_sp2, tss_struct, x86_tss.sp2);
+
+	if (IS_ENABLED(CONFIG_KVM_INTEL)) {
+		BLANK();
+		OFFSET(VMX_spec_ctrl, vcpu_vmx, spec_ctrl);
+	}
 }
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@ -862,6 +862,28 @@ static void init_amd_bd(struct cpuinfo_x86 *c)
 	clear_rdrand_cpuid_bit(c);
 }

+void init_spectral_chicken(struct cpuinfo_x86 *c)
+{
+#ifdef CONFIG_CPU_UNRET_ENTRY
+	u64 value;
+
+	/*
+	 * On Zen2 we offer this chicken (bit) on the altar of Speculation.
+	 *
+	 * This suppresses speculation from the middle of a basic block, i.e. it
+	 * suppresses non-branch predictions.
+	 *
+	 * We use STIBP as a heuristic to filter out Zen2 from the rest of F17H
+	 */
+	if (!cpu_has(c, X86_FEATURE_HYPERVISOR) && cpu_has(c, X86_FEATURE_AMD_STIBP)) {
+		if (!rdmsrl_safe(MSR_ZEN2_SPECTRAL_CHICKEN, &value)) {
+			value |= MSR_ZEN2_SPECTRAL_CHICKEN_BIT;
+			wrmsrl_safe(MSR_ZEN2_SPECTRAL_CHICKEN, value);
+		}
+	}
+#endif
+}
+
 static void init_amd_zn(struct cpuinfo_x86 *c)
 {
 	set_cpu_cap(c, X86_FEATURE_ZEN);
@ -870,12 +892,21 @@ static void init_amd_zn(struct cpuinfo_x86 *c)
 	node_reclaim_distance = 32;
 #endif

-	/*
-	 * Fix erratum 1076: CPB feature bit not being set in CPUID.
-	 * Always set it, except when running under a hypervisor.
-	 */
-	if (!cpu_has(c, X86_FEATURE_HYPERVISOR) && !cpu_has(c, X86_FEATURE_CPB))
-		set_cpu_cap(c, X86_FEATURE_CPB);
+	/* Fix up CPUID bits, but only if not virtualised. */
+	if (!cpu_has(c, X86_FEATURE_HYPERVISOR)) {
+
+		/* Erratum 1076: CPB feature bit not being set in CPUID. */
+		if (!cpu_has(c, X86_FEATURE_CPB))
+			set_cpu_cap(c, X86_FEATURE_CPB);
+
+		/*
+		 * Zen3 (Fam19 model < 0x10) parts are not susceptible to
+		 * Branch Type Confusion, but predate the allocation of the
+		 * BTC_NO bit.
+		 */
+		if (c->x86 == 0x19 && !cpu_has(c, X86_FEATURE_BTC_NO))
+			set_cpu_cap(c, X86_FEATURE_BTC_NO);
+	}
 }

 static void init_amd(struct cpuinfo_x86 *c)
@ -907,7 +938,8 @@ static void init_amd(struct cpuinfo_x86 *c)
 	case 0x12: init_amd_ln(c); break;
 	case 0x15: init_amd_bd(c); break;
 	case 0x16: init_amd_jg(c); break;
-	case 0x17: fallthrough;
+	case 0x17: init_spectral_chicken(c);
+		   fallthrough;
 	case 0x19: init_amd_zn(c); break;
 	}

--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@ -38,6 +38,8 @@

 static void __init spectre_v1_select_mitigation(void);
 static void __init spectre_v2_select_mitigation(void);
+static void __init retbleed_select_mitigation(void);
+static void __init spectre_v2_user_select_mitigation(void);
 static void __init ssb_select_mitigation(void);
 static void __init l1tf_select_mitigation(void);
 static void __init mds_select_mitigation(void);
@ -48,16 +50,40 @@ static void __init mmio_select_mitigation(void);
 static void __init srbds_select_mitigation(void);
 static void __init l1d_flush_select_mitigation(void);

-/* The base value of the SPEC_CTRL MSR that always has to be preserved. */
+/* The base value of the SPEC_CTRL MSR without task-specific bits set */
 u64 x86_spec_ctrl_base;
 EXPORT_SYMBOL_GPL(x86_spec_ctrl_base);
+
+/* The current value of the SPEC_CTRL MSR with task-specific bits set */
+DEFINE_PER_CPU(u64, x86_spec_ctrl_current);
+EXPORT_SYMBOL_GPL(x86_spec_ctrl_current);
+
 static DEFINE_MUTEX(spec_ctrl_mutex);

 /*
- * The vendor and possibly platform specific bits which can be modified in
- * x86_spec_ctrl_base.
+ * Keep track of the SPEC_CTRL MSR value for the current task, which may differ
+ * from x86_spec_ctrl_base due to STIBP/SSB in __speculation_ctrl_update().
 */
-static u64 __ro_after_init x86_spec_ctrl_mask = SPEC_CTRL_IBRS;
+void write_spec_ctrl_current(u64 val, bool force)
+{
+	if (this_cpu_read(x86_spec_ctrl_current) == val)
+		return;
+
+	this_cpu_write(x86_spec_ctrl_current, val);
+
+	/*
+	 * When KERNEL_IBRS this MSR is written on return-to-user, unless
+	 * forced the update can be delayed until that time.
+	 */
+	if (force || !cpu_feature_enabled(X86_FEATURE_KERNEL_IBRS))
+		wrmsrl(MSR_IA32_SPEC_CTRL, val);
+}
+
+u64 spec_ctrl_current(void)
+{
+	return this_cpu_read(x86_spec_ctrl_current);
+}
+EXPORT_SYMBOL_GPL(spec_ctrl_current);

 /*
 * AMD specific MSR info for Speculative Store Bypass control.
@ -114,13 +140,21 @@ void __init check_bugs(void)
 	if (boot_cpu_has(X86_FEATURE_MSR_SPEC_CTRL))
 		rdmsrl(MSR_IA32_SPEC_CTRL, x86_spec_ctrl_base);

-	/* Allow STIBP in MSR_SPEC_CTRL if supported */
-	if (boot_cpu_has(X86_FEATURE_STIBP))
-		x86_spec_ctrl_mask |= SPEC_CTRL_STIBP;
-
 	/* Select the proper CPU mitigations before patching alternatives: */
 	spectre_v1_select_mitigation();
 	spectre_v2_select_mitigation();
+	/*
+	 * retbleed_select_mitigation() relies on the state set by
+	 * spectre_v2_select_mitigation(); specifically it wants to know about
+	 * spectre_v2=ibrs.
+	 */
+	retbleed_select_mitigation();
+	/*
+	 * spectre_v2_user_select_mitigation() relies on the state set by
+	 * retbleed_select_mitigation(); specifically the STIBP selection is
+	 * forced for UNRET.
+	 */
+	spectre_v2_user_select_mitigation();
 	ssb_select_mitigation();
 	l1tf_select_mitigation();
 	md_clear_select_mitigation();
@ -161,31 +195,17 @@ void __init check_bugs(void)
 #endif
 }

+/*
+ * NOTE: This function is *only* called for SVM.  VMX spec_ctrl handling is
+ * done in vmenter.S.
+ */
 void
 x86_virt_spec_ctrl(u64 guest_spec_ctrl, u64 guest_virt_spec_ctrl, bool setguest)
 {
-	u64 msrval, guestval, hostval = x86_spec_ctrl_base;
+	u64 msrval, guestval = guest_spec_ctrl, hostval = spec_ctrl_current();
 	struct thread_info *ti = current_thread_info();

-	/* Is MSR_SPEC_CTRL implemented ? */
 	if (static_cpu_has(X86_FEATURE_MSR_SPEC_CTRL)) {
-		/*
-		 * Restrict guest_spec_ctrl to supported values. Clear the
-		 * modifiable bits in the host base value and or the
-		 * modifiable bits from the guest value.
-		 */
-		guestval = hostval & ~x86_spec_ctrl_mask;
-		guestval |= guest_spec_ctrl & x86_spec_ctrl_mask;
-
-		/* SSBD controlled in MSR_SPEC_CTRL */
-		if (static_cpu_has(X86_FEATURE_SPEC_CTRL_SSBD) ||
-		    static_cpu_has(X86_FEATURE_AMD_SSBD))
-			hostval |= ssbd_tif_to_spec_ctrl(ti->flags);
-
-		/* Conditional STIBP enabled? */
-		if (static_branch_unlikely(&switch_to_cond_stibp))
-			hostval |= stibp_tif_to_spec_ctrl(ti->flags);
-
 		if (hostval != guestval) {
 			msrval = setguest ? guestval : hostval;
 			wrmsrl(MSR_IA32_SPEC_CTRL, msrval);
@ -752,12 +772,180 @@ static int __init nospectre_v1_cmdline(char *str)
 }
 early_param("nospectre_v1", nospectre_v1_cmdline);

-#undef pr_fmt
-#define pr_fmt(fmt)     "Spectre V2 : " fmt
-
 static enum spectre_v2_mitigation spectre_v2_enabled __ro_after_init =
 	SPECTRE_V2_NONE;

+#undef pr_fmt
+#define pr_fmt(fmt)     "RETBleed: " fmt
+
+enum retbleed_mitigation {
+	RETBLEED_MITIGATION_NONE,
+	RETBLEED_MITIGATION_UNRET,
+	RETBLEED_MITIGATION_IBPB,
+	RETBLEED_MITIGATION_IBRS,
+	RETBLEED_MITIGATION_EIBRS,
+};
+
+enum retbleed_mitigation_cmd {
+	RETBLEED_CMD_OFF,
+	RETBLEED_CMD_AUTO,
+	RETBLEED_CMD_UNRET,
+	RETBLEED_CMD_IBPB,
+};
+
+const char * const retbleed_strings[] = {
+	[RETBLEED_MITIGATION_NONE]	= "Vulnerable",
+	[RETBLEED_MITIGATION_UNRET]	= "Mitigation: untrained return thunk",
+	[RETBLEED_MITIGATION_IBPB]	= "Mitigation: IBPB",
+	[RETBLEED_MITIGATION_IBRS]	= "Mitigation: IBRS",
+	[RETBLEED_MITIGATION_EIBRS]	= "Mitigation: Enhanced IBRS",
+};
+
+static enum retbleed_mitigation retbleed_mitigation __ro_after_init =
+	RETBLEED_MITIGATION_NONE;
+static enum retbleed_mitigation_cmd retbleed_cmd __ro_after_init =
+	RETBLEED_CMD_AUTO;
+
+static int __ro_after_init retbleed_nosmt = false;
+
+static int __init retbleed_parse_cmdline(char *str)
+{
+	if (!str)
+		return -EINVAL;
+
+	while (str) {
+		char *next = strchr(str, ',');
+		if (next) {
+			*next = 0;
+			next++;
+		}
+
+		if (!strcmp(str, "off")) {
+			retbleed_cmd = RETBLEED_CMD_OFF;
+		} else if (!strcmp(str, "auto")) {
+			retbleed_cmd = RETBLEED_CMD_AUTO;
+		} else if (!strcmp(str, "unret")) {
+			retbleed_cmd = RETBLEED_CMD_UNRET;
+		} else if (!strcmp(str, "ibpb")) {
+			retbleed_cmd = RETBLEED_CMD_IBPB;
+		} else if (!strcmp(str, "nosmt")) {
+			retbleed_nosmt = true;
+		} else {
+			pr_err("Ignoring unknown retbleed option (%s).", str);
+		}
+
+		str = next;
+	}
+
+	return 0;
+}
+early_param("retbleed", retbleed_parse_cmdline);
+
+#define RETBLEED_UNTRAIN_MSG "WARNING: BTB untrained return thunk mitigation is only effective on AMD/Hygon!\n"
+#define RETBLEED_INTEL_MSG "WARNING: Spectre v2 mitigation leaves CPU vulnerable to RETBleed attacks, data leaks possible!\n"
+
+static void __init retbleed_select_mitigation(void)
+{
+	bool mitigate_smt = false;
+
+	if (!boot_cpu_has_bug(X86_BUG_RETBLEED) || cpu_mitigations_off())
+		return;
+
+	switch (retbleed_cmd) {
+	case RETBLEED_CMD_OFF:
+		return;
+
+	case RETBLEED_CMD_UNRET:
+		if (IS_ENABLED(CONFIG_CPU_UNRET_ENTRY)) {
+			retbleed_mitigation = RETBLEED_MITIGATION_UNRET;
+		} else {
+			pr_err("WARNING: kernel not compiled with CPU_UNRET_ENTRY.\n");
+			goto do_cmd_auto;
+		}
+		break;
+
+	case RETBLEED_CMD_IBPB:
+		if (!boot_cpu_has(X86_FEATURE_IBPB)) {
+			pr_err("WARNING: CPU does not support IBPB.\n");
+			goto do_cmd_auto;
+		} else if (IS_ENABLED(CONFIG_CPU_IBPB_ENTRY)) {
+			retbleed_mitigation = RETBLEED_MITIGATION_IBPB;
+		} else {
+			pr_err("WARNING: kernel not compiled with CPU_IBPB_ENTRY.\n");
+			goto do_cmd_auto;
+		}
+		break;
+
+do_cmd_auto:
+	case RETBLEED_CMD_AUTO:
+	default:
+		if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD ||
+		    boot_cpu_data.x86_vendor == X86_VENDOR_HYGON) {
+			if (IS_ENABLED(CONFIG_CPU_UNRET_ENTRY))
+				retbleed_mitigation = RETBLEED_MITIGATION_UNRET;
+			else if (IS_ENABLED(CONFIG_CPU_IBPB_ENTRY) && boot_cpu_has(X86_FEATURE_IBPB))
+				retbleed_mitigation = RETBLEED_MITIGATION_IBPB;
+		}
+
+		/*
+		 * The Intel mitigation (IBRS or eIBRS) was already selected in
+		 * spectre_v2_select_mitigation().  'retbleed_mitigation' will
+		 * be set accordingly below.
+		 */
+
+		break;
+	}
+
+	switch (retbleed_mitigation) {
+	case RETBLEED_MITIGATION_UNRET:
+		setup_force_cpu_cap(X86_FEATURE_RETHUNK);
+		setup_force_cpu_cap(X86_FEATURE_UNRET);
+
+		if (boot_cpu_data.x86_vendor != X86_VENDOR_AMD &&
+		    boot_cpu_data.x86_vendor != X86_VENDOR_HYGON)
+			pr_err(RETBLEED_UNTRAIN_MSG);
+
+		mitigate_smt = true;
+		break;
+
+	case RETBLEED_MITIGATION_IBPB:
+		setup_force_cpu_cap(X86_FEATURE_ENTRY_IBPB);
+		mitigate_smt = true;
+		break;
+
+	default:
+		break;
+	}
+
+	if (mitigate_smt && !boot_cpu_has(X86_FEATURE_STIBP) &&
+	    (retbleed_nosmt || cpu_mitigations_auto_nosmt()))
+		cpu_smt_disable(false);
+
+	/*
+	 * Let IBRS trump all on Intel without affecting the effects of the
+	 * retbleed= cmdline option.
+	 */
+	if (boot_cpu_data.x86_vendor == X86_VENDOR_INTEL) {
+		switch (spectre_v2_enabled) {
+		case SPECTRE_V2_IBRS:
+			retbleed_mitigation = RETBLEED_MITIGATION_IBRS;
+			break;
+		case SPECTRE_V2_EIBRS:
+		case SPECTRE_V2_EIBRS_RETPOLINE:
+		case SPECTRE_V2_EIBRS_LFENCE:
+			retbleed_mitigation = RETBLEED_MITIGATION_EIBRS;
+			break;
+		default:
+			pr_err(RETBLEED_INTEL_MSG);
+		}
+	}
+
+	pr_info("%s\n", retbleed_strings[retbleed_mitigation]);
+}
+
+#undef pr_fmt
+#define pr_fmt(fmt)     "Spectre V2 : " fmt
+
 static enum spectre_v2_user_mitigation spectre_v2_user_stibp __ro_after_init =
 	SPECTRE_V2_USER_NONE;
 static enum spectre_v2_user_mitigation spectre_v2_user_ibpb __ro_after_init =
@ -828,6 +1016,7 @@ enum spectre_v2_mitigation_cmd {
 	SPECTRE_V2_CMD_EIBRS,
 	SPECTRE_V2_CMD_EIBRS_RETPOLINE,
 	SPECTRE_V2_CMD_EIBRS_LFENCE,
+	SPECTRE_V2_CMD_IBRS,
 };

 enum spectre_v2_user_cmd {
@ -868,13 +1057,15 @@ static void __init spec_v2_user_print_cond(const char *reason, bool secure)
 		pr_info("spectre_v2_user=%s forced on command line.\n", reason);
 }

+static __ro_after_init enum spectre_v2_mitigation_cmd spectre_v2_cmd;
+
 static enum spectre_v2_user_cmd __init
-spectre_v2_parse_user_cmdline(enum spectre_v2_mitigation_cmd v2_cmd)
+spectre_v2_parse_user_cmdline(void)
 {
 	char arg[20];
 	int ret, i;

-	switch (v2_cmd) {
+	switch (spectre_v2_cmd) {
 	case SPECTRE_V2_CMD_NONE:
 		return SPECTRE_V2_USER_CMD_NONE;
 	case SPECTRE_V2_CMD_FORCE:
@ -900,15 +1091,16 @@ spectre_v2_parse_user_cmdline(enum spectre_v2_mitigation_cmd v2_cmd)
 	return SPECTRE_V2_USER_CMD_AUTO;
 }

-static inline bool spectre_v2_in_eibrs_mode(enum spectre_v2_mitigation mode)
+static inline bool spectre_v2_in_ibrs_mode(enum spectre_v2_mitigation mode)
 {
-	return (mode == SPECTRE_V2_EIBRS ||
-		mode == SPECTRE_V2_EIBRS_RETPOLINE ||
-		mode == SPECTRE_V2_EIBRS_LFENCE);
+	return mode == SPECTRE_V2_IBRS ||
+	       mode == SPECTRE_V2_EIBRS ||
+	       mode == SPECTRE_V2_EIBRS_RETPOLINE ||
+	       mode == SPECTRE_V2_EIBRS_LFENCE;
 }

 static void __init
-spectre_v2_user_select_mitigation(enum spectre_v2_mitigation_cmd v2_cmd)
+spectre_v2_user_select_mitigation(void)
 {
 	enum spectre_v2_user_mitigation mode = SPECTRE_V2_USER_NONE;
 	bool smt_possible = IS_ENABLED(CONFIG_SMP);
@ -921,7 +1113,7 @@ spectre_v2_user_select_mitigation(enum spectre_v2_mitigation_cmd v2_cmd)
 	    cpu_smt_control == CPU_SMT_NOT_SUPPORTED)
 		smt_possible = false;

-	cmd = spectre_v2_parse_user_cmdline(v2_cmd);
+	cmd = spectre_v2_parse_user_cmdline();
 	switch (cmd) {
 	case SPECTRE_V2_USER_CMD_NONE:
 		goto set_mode;
@ -969,12 +1161,12 @@ spectre_v2_user_select_mitigation(enum spectre_v2_mitigation_cmd v2_cmd)
 	}

 	/*
-	 * If no STIBP, enhanced IBRS is enabled or SMT impossible, STIBP is not
-	 * required.
+	 * If no STIBP, IBRS or enhanced IBRS is enabled, or SMT impossible,
+	 * STIBP is not required.
 	 */
 	if (!boot_cpu_has(X86_FEATURE_STIBP) ||
 	    !smt_possible ||
-	    spectre_v2_in_eibrs_mode(spectre_v2_enabled))
+	    spectre_v2_in_ibrs_mode(spectre_v2_enabled))
 		return;

 	/*
@ -986,6 +1178,13 @@ spectre_v2_user_select_mitigation(enum spectre_v2_mitigation_cmd v2_cmd)
 	    boot_cpu_has(X86_FEATURE_AMD_STIBP_ALWAYS_ON))
 		mode = SPECTRE_V2_USER_STRICT_PREFERRED;

+	if (retbleed_mitigation == RETBLEED_MITIGATION_UNRET) {
+		if (mode != SPECTRE_V2_USER_STRICT &&
+		    mode != SPECTRE_V2_USER_STRICT_PREFERRED)
+			pr_info("Selecting STIBP always-on mode to complement retbleed mitigation'\n");
+		mode = SPECTRE_V2_USER_STRICT_PREFERRED;
+	}
+
 	spectre_v2_user_stibp = mode;

 set_mode:
@ -999,6 +1198,7 @@ static const char * const spectre_v2_strings[] = {
 	[SPECTRE_V2_EIBRS]			= "Mitigation: Enhanced IBRS",
 	[SPECTRE_V2_EIBRS_LFENCE]		= "Mitigation: Enhanced IBRS + LFENCE",
 	[SPECTRE_V2_EIBRS_RETPOLINE]		= "Mitigation: Enhanced IBRS + Retpolines",
+	[SPECTRE_V2_IBRS]			= "Mitigation: IBRS",
 };

 static const struct {
@ -1016,6 +1216,7 @@ static const struct {
 	{ "eibrs,lfence",	SPECTRE_V2_CMD_EIBRS_LFENCE,	  false },
 	{ "eibrs,retpoline",	SPECTRE_V2_CMD_EIBRS_RETPOLINE,	  false },
 	{ "auto",		SPECTRE_V2_CMD_AUTO,		  false },
+	{ "ibrs",		SPECTRE_V2_CMD_IBRS,              false },
 };

 static void __init spec_v2_print_cond(const char *reason, bool secure)
@ -1078,6 +1279,30 @@ static enum spectre_v2_mitigation_cmd __init spectre_v2_parse_cmdline(void)
 		return SPECTRE_V2_CMD_AUTO;
 	}

+	if (cmd == SPECTRE_V2_CMD_IBRS && !IS_ENABLED(CONFIG_CPU_IBRS_ENTRY)) {
+		pr_err("%s selected but not compiled in. Switching to AUTO select\n",
+		       mitigation_options[i].option);
+		return SPECTRE_V2_CMD_AUTO;
+	}
+
+	if (cmd == SPECTRE_V2_CMD_IBRS && boot_cpu_data.x86_vendor != X86_VENDOR_INTEL) {
+		pr_err("%s selected but not Intel CPU. Switching to AUTO select\n",
+		       mitigation_options[i].option);
+		return SPECTRE_V2_CMD_AUTO;
+	}
+
+	if (cmd == SPECTRE_V2_CMD_IBRS && !boot_cpu_has(X86_FEATURE_IBRS)) {
+		pr_err("%s selected but CPU doesn't have IBRS. Switching to AUTO select\n",
+		       mitigation_options[i].option);
+		return SPECTRE_V2_CMD_AUTO;
+	}
+
+	if (cmd == SPECTRE_V2_CMD_IBRS && boot_cpu_has(X86_FEATURE_XENPV)) {
+		pr_err("%s selected but running as XenPV guest. Switching to AUTO select\n",
+		       mitigation_options[i].option);
+		return SPECTRE_V2_CMD_AUTO;
+	}
+
 	spec_v2_print_cond(mitigation_options[i].option,
 			   mitigation_options[i].secure);
 	return cmd;
@ -1093,6 +1318,22 @@ static enum spectre_v2_mitigation __init spectre_v2_select_retpoline(void)
 	return SPECTRE_V2_RETPOLINE;
 }

+/* Disable in-kernel use of non-RSB RET predictors */
+static void __init spec_ctrl_disable_kernel_rrsba(void)
+{
+	u64 ia32_cap;
+
+	if (!boot_cpu_has(X86_FEATURE_RRSBA_CTRL))
+		return;
+
+	ia32_cap = x86_read_arch_cap_msr();
+
+	if (ia32_cap & ARCH_CAP_RRSBA) {
+		x86_spec_ctrl_base |= SPEC_CTRL_RRSBA_DIS_S;
+		write_spec_ctrl_current(x86_spec_ctrl_base, true);
+	}
+}
+
 static void __init spectre_v2_select_mitigation(void)
 {
 	enum spectre_v2_mitigation_cmd cmd = spectre_v2_parse_cmdline();
@ -1117,6 +1358,15 @@ static void __init spectre_v2_select_mitigation(void)
 			break;
 		}

+		if (IS_ENABLED(CONFIG_CPU_IBRS_ENTRY) &&
+		    boot_cpu_has_bug(X86_BUG_RETBLEED) &&
+		    retbleed_cmd != RETBLEED_CMD_OFF &&
+		    boot_cpu_has(X86_FEATURE_IBRS) &&
+		    boot_cpu_data.x86_vendor == X86_VENDOR_INTEL) {
+			mode = SPECTRE_V2_IBRS;
+			break;
+		}
+
 		mode = spectre_v2_select_retpoline();
 		break;

@ -1133,6 +1383,10 @@ static void __init spectre_v2_select_mitigation(void)
 		mode = spectre_v2_select_retpoline();
 		break;

+	case SPECTRE_V2_CMD_IBRS:
+		mode = SPECTRE_V2_IBRS;
+		break;
+
 	case SPECTRE_V2_CMD_EIBRS:
 		mode = SPECTRE_V2_EIBRS;
 		break;
@ -1149,10 +1403,9 @@ static void __init spectre_v2_select_mitigation(void)
 	if (mode == SPECTRE_V2_EIBRS && unprivileged_ebpf_enabled())
 		pr_err(SPECTRE_V2_EIBRS_EBPF_MSG);

-	if (spectre_v2_in_eibrs_mode(mode)) {
-		/* Force it so VMEXIT will restore correctly */
+	if (spectre_v2_in_ibrs_mode(mode)) {
 		x86_spec_ctrl_base |= SPEC_CTRL_IBRS;
-		wrmsrl(MSR_IA32_SPEC_CTRL, x86_spec_ctrl_base);
+		write_spec_ctrl_current(x86_spec_ctrl_base, true);
 	}

 	switch (mode) {
@ -1160,6 +1413,10 @@ static void __init spectre_v2_select_mitigation(void)
 	case SPECTRE_V2_EIBRS:
 		break;

+	case SPECTRE_V2_IBRS:
+		setup_force_cpu_cap(X86_FEATURE_KERNEL_IBRS);
+		break;
+
 	case SPECTRE_V2_LFENCE:
 	case SPECTRE_V2_EIBRS_LFENCE:
 		setup_force_cpu_cap(X86_FEATURE_RETPOLINE_LFENCE);
@ -1171,43 +1428,107 @@ static void __init spectre_v2_select_mitigation(void)
 		break;
 	}

+	/*
+	 * Disable alternate RSB predictions in kernel when indirect CALLs and
+	 * JMPs gets protection against BHI and Intramode-BTI, but RET
+	 * prediction from a non-RSB predictor is still a risk.
+	 */
+	if (mode == SPECTRE_V2_EIBRS_LFENCE ||
+	    mode == SPECTRE_V2_EIBRS_RETPOLINE ||
+	    mode == SPECTRE_V2_RETPOLINE)
+		spec_ctrl_disable_kernel_rrsba();
+
 	spectre_v2_enabled = mode;
 	pr_info("%s\n", spectre_v2_strings[mode]);

 	/*
-	 * If spectre v2 protection has been enabled, unconditionally fill
-	 * RSB during a context switch; this protects against two independent
-	 * issues:
+	 * If Spectre v2 protection has been enabled, fill the RSB during a
+	 * context switch.  In general there are two types of RSB attacks
+	 * across context switches, for which the CALLs/RETs may be unbalanced.
 	 *
-	 *	- RSB underflow (and switch to BTB) on Skylake+
-	 *	- SpectreRSB variant of spectre v2 on X86_BUG_SPECTRE_V2 CPUs
+	 * 1) RSB underflow
+	 *
+	 *    Some Intel parts have "bottomless RSB".  When the RSB is empty,
+	 *    speculated return targets may come from the branch predictor,
+	 *    which could have a user-poisoned BTB or BHB entry.
+	 *
+	 *    AMD has it even worse: *all* returns are speculated from the BTB,
+	 *    regardless of the state of the RSB.
+	 *
+	 *    When IBRS or eIBRS is enabled, the "user -> kernel" attack
+	 *    scenario is mitigated by the IBRS branch prediction isolation
+	 *    properties, so the RSB buffer filling wouldn't be necessary to
+	 *    protect against this type of attack.
+	 *
+	 *    The "user -> user" attack scenario is mitigated by RSB filling.
+	 *
+	 * 2) Poisoned RSB entry
+	 *
+	 *    If the 'next' in-kernel return stack is shorter than 'prev',
+	 *    'next' could be tricked into speculating with a user-poisoned RSB
+	 *    entry.
+	 *
+	 *    The "user -> kernel" attack scenario is mitigated by SMEP and
+	 *    eIBRS.
+	 *
+	 *    The "user -> user" scenario, also known as SpectreBHB, requires
+	 *    RSB clearing.
+	 *
+	 * So to mitigate all cases, unconditionally fill RSB on context
+	 * switches.
+	 *
+	 * FIXME: Is this pointless for retbleed-affected AMD?
 	 */
 	setup_force_cpu_cap(X86_FEATURE_RSB_CTXSW);
 	pr_info("Spectre v2 / SpectreRSB mitigation: Filling RSB on context switch\n");

 	/*
-	 * Retpoline means the kernel is safe because it has no indirect
-	 * branches. Enhanced IBRS protects firmware too, so, enable restricted
-	 * speculation around firmware calls only when Enhanced IBRS isn't
-	 * supported.
+	 * Similar to context switches, there are two types of RSB attacks
+	 * after vmexit:
+	 *
+	 * 1) RSB underflow
+	 *
+	 * 2) Poisoned RSB entry
+	 *
+	 * When retpoline is enabled, both are mitigated by filling/clearing
+	 * the RSB.
+	 *
+	 * When IBRS is enabled, while #1 would be mitigated by the IBRS branch
+	 * prediction isolation protections, RSB still needs to be cleared
+	 * because of #2.  Note that SMEP provides no protection here, unlike
+	 * user-space-poisoned RSB entries.
+	 *
+	 * eIBRS, on the other hand, has RSB-poisoning protections, so it
+	 * doesn't need RSB clearing after vmexit.
+	 */
+	if (boot_cpu_has(X86_FEATURE_RETPOLINE) ||
+	    boot_cpu_has(X86_FEATURE_KERNEL_IBRS))
+		setup_force_cpu_cap(X86_FEATURE_RSB_VMEXIT);
+
+	/*
+	 * Retpoline protects the kernel, but doesn't protect firmware.  IBRS
+	 * and Enhanced IBRS protect firmware too, so enable IBRS around
+	 * firmware calls only when IBRS / Enhanced IBRS aren't otherwise
+	 * enabled.
 	 *
 	 * Use "mode" to check Enhanced IBRS instead of boot_cpu_has(), because
 	 * the user might select retpoline on the kernel command line and if
 	 * the CPU supports Enhanced IBRS, kernel might un-intentionally not
 	 * enable IBRS around firmware calls.
 	 */
-	if (boot_cpu_has(X86_FEATURE_IBRS) && !spectre_v2_in_eibrs_mode(mode)) {
+	if (boot_cpu_has(X86_FEATURE_IBRS) && !spectre_v2_in_ibrs_mode(mode)) {
 		setup_force_cpu_cap(X86_FEATURE_USE_IBRS_FW);
 		pr_info("Enabling Restricted Speculation for firmware calls\n");
 	}

 	/* Set up IBPB and STIBP depending on the general spectre V2 command */
-	spectre_v2_user_select_mitigation(cmd);
+	spectre_v2_cmd = cmd;
 }

 static void update_stibp_msr(void * __unused)
 {
-	wrmsrl(MSR_IA32_SPEC_CTRL, x86_spec_ctrl_base);
+	u64 val = spec_ctrl_current() | (x86_spec_ctrl_base & SPEC_CTRL_STIBP);
+	write_spec_ctrl_current(val, true);
 }

 /* Update x86_spec_ctrl_base in case SMT state changed. */
@ -1423,16 +1744,6 @@ static enum ssb_mitigation __init __ssb_select_mitigation(void)
 		break;
 	}

-	/*
-	 * If SSBD is controlled by the SPEC_CTRL MSR, then set the proper
-	 * bit in the mask to allow guests to use the mitigation even in the
-	 * case where the host does not enable it.
-	 */
-	if (static_cpu_has(X86_FEATURE_SPEC_CTRL_SSBD) ||
-	    static_cpu_has(X86_FEATURE_AMD_SSBD)) {
-		x86_spec_ctrl_mask |= SPEC_CTRL_SSBD;
-	}
-
 	/*
 	 * We have three CPU feature flags that are in play here:
 	 *  - X86_BUG_SPEC_STORE_BYPASS - CPU is susceptible.
@ -1450,7 +1761,7 @@ static enum ssb_mitigation __init __ssb_select_mitigation(void)
 			x86_amd_ssb_disable();
 		} else {
 			x86_spec_ctrl_base |= SPEC_CTRL_SSBD;
-			wrmsrl(MSR_IA32_SPEC_CTRL, x86_spec_ctrl_base);
+			write_spec_ctrl_current(x86_spec_ctrl_base, true);
 		}
 	}

@ -1701,7 +2012,7 @@ int arch_prctl_spec_ctrl_get(struct task_struct *task, unsigned long which)
 void x86_spec_ctrl_setup_ap(void)
 {
 	if (boot_cpu_has(X86_FEATURE_MSR_SPEC_CTRL))
-		wrmsrl(MSR_IA32_SPEC_CTRL, x86_spec_ctrl_base);
+		write_spec_ctrl_current(x86_spec_ctrl_base, true);

 	if (ssb_mode == SPEC_STORE_BYPASS_DISABLE)
 		x86_amd_ssb_disable();
@ -1938,7 +2249,7 @@ static ssize_t mmio_stale_data_show_state(char *buf)

 static char *stibp_state(void)
 {
-	if (spectre_v2_in_eibrs_mode(spectre_v2_enabled))
+	if (spectre_v2_in_ibrs_mode(spectre_v2_enabled))
 		return "";

 	switch (spectre_v2_user_stibp) {
@ -1994,6 +2305,24 @@ static ssize_t srbds_show_state(char *buf)
 	return sprintf(buf, "%s\n", srbds_strings[srbds_mitigation]);
 }

+static ssize_t retbleed_show_state(char *buf)
+{
+	if (retbleed_mitigation == RETBLEED_MITIGATION_UNRET) {
+	    if (boot_cpu_data.x86_vendor != X86_VENDOR_AMD &&
+		boot_cpu_data.x86_vendor != X86_VENDOR_HYGON)
+		    return sprintf(buf, "Vulnerable: untrained return thunk on non-Zen uarch\n");
+
+	    return sprintf(buf, "%s; SMT %s\n",
+			   retbleed_strings[retbleed_mitigation],
+			   !sched_smt_active() ? "disabled" :
+			   spectre_v2_user_stibp == SPECTRE_V2_USER_STRICT ||
+			   spectre_v2_user_stibp == SPECTRE_V2_USER_STRICT_PREFERRED ?
+			   "enabled with STIBP protection" : "vulnerable");
+	}
+
+	return sprintf(buf, "%s\n", retbleed_strings[retbleed_mitigation]);
+}
+
 static ssize_t cpu_show_common(struct device *dev, struct device_attribute *attr,
 			       char *buf, unsigned int bug)
 {
@ -2039,6 +2368,9 @@ static ssize_t cpu_show_common(struct device *dev, struct device_attribute *attr
 	case X86_BUG_MMIO_STALE_DATA:
 		return mmio_stale_data_show_state(buf);

+	case X86_BUG_RETBLEED:
+		return retbleed_show_state(buf);
+
 	default:
 		break;
 	}
@ -2095,4 +2427,9 @@ ssize_t cpu_show_mmio_stale_data(struct device *dev, struct device_attribute *at
 {
 	return cpu_show_common(dev, attr, buf, X86_BUG_MMIO_STALE_DATA);
 }
+
+ssize_t cpu_show_retbleed(struct device *dev, struct device_attribute *attr, char *buf)
+{
+	return cpu_show_common(dev, attr, buf, X86_BUG_RETBLEED);
+}
 #endif
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@ -1205,48 +1205,60 @@ static const __initconst struct x86_cpu_id cpu_vuln_whitelist[] = {
 	{}
 };

+#define VULNBL(vendor, family, model, blacklist)	\
+	X86_MATCH_VENDOR_FAM_MODEL(vendor, family, model, blacklist)
+
 #define VULNBL_INTEL_STEPPINGS(model, steppings, issues)		   \
 	X86_MATCH_VENDOR_FAM_MODEL_STEPPINGS_FEATURE(INTEL, 6,		   \
 					    INTEL_FAM6_##model, steppings, \
 					    X86_FEATURE_ANY, issues)

+#define VULNBL_AMD(family, blacklist)		\
+	VULNBL(AMD, family, X86_MODEL_ANY, blacklist)
+
+#define VULNBL_HYGON(family, blacklist)		\
+	VULNBL(HYGON, family, X86_MODEL_ANY, blacklist)
+
 #define SRBDS		BIT(0)
 /* CPU is affected by X86_BUG_MMIO_STALE_DATA */
 #define MMIO		BIT(1)
 /* CPU is affected by Shared Buffers Data Sampling (SBDS), a variant of X86_BUG_MMIO_STALE_DATA */
 #define MMIO_SBDS	BIT(2)
+/* CPU is affected by RETbleed, speculating where you would not expect it */
+#define RETBLEED	BIT(3)

 static const struct x86_cpu_id cpu_vuln_blacklist[] __initconst = {
 	VULNBL_INTEL_STEPPINGS(IVYBRIDGE,	X86_STEPPING_ANY,		SRBDS),
 	VULNBL_INTEL_STEPPINGS(HASWELL,		X86_STEPPING_ANY,		SRBDS),
 	VULNBL_INTEL_STEPPINGS(HASWELL_L,	X86_STEPPING_ANY,		SRBDS),
 	VULNBL_INTEL_STEPPINGS(HASWELL_G,	X86_STEPPING_ANY,		SRBDS),
-	VULNBL_INTEL_STEPPINGS(HASWELL_X,	BIT(2) | BIT(4),		MMIO),
-	VULNBL_INTEL_STEPPINGS(BROADWELL_D,	X86_STEPPINGS(0x3, 0x5),	MMIO),
+	VULNBL_INTEL_STEPPINGS(HASWELL_X,	X86_STEPPING_ANY,		MMIO),
+	VULNBL_INTEL_STEPPINGS(BROADWELL_D,	X86_STEPPING_ANY,		MMIO),
 	VULNBL_INTEL_STEPPINGS(BROADWELL_G,	X86_STEPPING_ANY,		SRBDS),
 	VULNBL_INTEL_STEPPINGS(BROADWELL_X,	X86_STEPPING_ANY,		MMIO),
 	VULNBL_INTEL_STEPPINGS(BROADWELL,	X86_STEPPING_ANY,		SRBDS),
-	VULNBL_INTEL_STEPPINGS(SKYLAKE_L,	X86_STEPPINGS(0x3, 0x3),	SRBDS | MMIO),
-	VULNBL_INTEL_STEPPINGS(SKYLAKE_L,	X86_STEPPING_ANY,		SRBDS),
-	VULNBL_INTEL_STEPPINGS(SKYLAKE_X,	BIT(3) | BIT(4) | BIT(6) |
-						BIT(7) | BIT(0xB),              MMIO),
-	VULNBL_INTEL_STEPPINGS(SKYLAKE,		X86_STEPPINGS(0x3, 0x3),	SRBDS | MMIO),
-	VULNBL_INTEL_STEPPINGS(SKYLAKE,		X86_STEPPING_ANY,		SRBDS),
-	VULNBL_INTEL_STEPPINGS(KABYLAKE_L,	X86_STEPPINGS(0x9, 0xC),	SRBDS | MMIO),
-	VULNBL_INTEL_STEPPINGS(KABYLAKE_L,	X86_STEPPINGS(0x0, 0x8),	SRBDS),
-	VULNBL_INTEL_STEPPINGS(KABYLAKE,	X86_STEPPINGS(0x9, 0xD),	SRBDS | MMIO),
-	VULNBL_INTEL_STEPPINGS(KABYLAKE,	X86_STEPPINGS(0x0, 0x8),	SRBDS),
-	VULNBL_INTEL_STEPPINGS(ICELAKE_L,	X86_STEPPINGS(0x5, 0x5),	MMIO | MMIO_SBDS),
-	VULNBL_INTEL_STEPPINGS(ICELAKE_D,	X86_STEPPINGS(0x1, 0x1),	MMIO),
-	VULNBL_INTEL_STEPPINGS(ICELAKE_X,	X86_STEPPINGS(0x4, 0x6),	MMIO),
-	VULNBL_INTEL_STEPPINGS(COMETLAKE,	BIT(2) | BIT(3) | BIT(5),	MMIO | MMIO_SBDS),
-	VULNBL_INTEL_STEPPINGS(COMETLAKE_L,	X86_STEPPINGS(0x1, 0x1),	MMIO | MMIO_SBDS),
-	VULNBL_INTEL_STEPPINGS(COMETLAKE_L,	X86_STEPPINGS(0x0, 0x0),	MMIO),
-	VULNBL_INTEL_STEPPINGS(LAKEFIELD,	X86_STEPPINGS(0x1, 0x1),	MMIO | MMIO_SBDS),
-	VULNBL_INTEL_STEPPINGS(ROCKETLAKE,	X86_STEPPINGS(0x1, 0x1),	MMIO),
-	VULNBL_INTEL_STEPPINGS(ATOM_TREMONT,	X86_STEPPINGS(0x1, 0x1),	MMIO | MMIO_SBDS),
+	VULNBL_INTEL_STEPPINGS(SKYLAKE_L,	X86_STEPPING_ANY,		SRBDS | MMIO | RETBLEED),
+	VULNBL_INTEL_STEPPINGS(SKYLAKE_X,	X86_STEPPING_ANY,		MMIO | RETBLEED),
+	VULNBL_INTEL_STEPPINGS(SKYLAKE,		X86_STEPPING_ANY,		SRBDS | MMIO | RETBLEED),
+	VULNBL_INTEL_STEPPINGS(KABYLAKE_L,	X86_STEPPING_ANY,		SRBDS | MMIO | RETBLEED),
+	VULNBL_INTEL_STEPPINGS(KABYLAKE,	X86_STEPPING_ANY,		SRBDS | MMIO | RETBLEED),
+	VULNBL_INTEL_STEPPINGS(CANNONLAKE_L,	X86_STEPPING_ANY,		RETBLEED),
+	VULNBL_INTEL_STEPPINGS(ICELAKE_L,	X86_STEPPING_ANY,		MMIO | MMIO_SBDS | RETBLEED),
+	VULNBL_INTEL_STEPPINGS(ICELAKE_D,	X86_STEPPING_ANY,		MMIO),
+	VULNBL_INTEL_STEPPINGS(ICELAKE_X,	X86_STEPPING_ANY,		MMIO),
+	VULNBL_INTEL_STEPPINGS(COMETLAKE,	X86_STEPPING_ANY,		MMIO | MMIO_SBDS | RETBLEED),
+	VULNBL_INTEL_STEPPINGS(COMETLAKE_L,	X86_STEPPINGS(0x0, 0x0),	MMIO | RETBLEED),
+	VULNBL_INTEL_STEPPINGS(COMETLAKE_L,	X86_STEPPING_ANY,		MMIO | MMIO_SBDS | RETBLEED),
+	VULNBL_INTEL_STEPPINGS(LAKEFIELD,	X86_STEPPING_ANY,		MMIO | MMIO_SBDS | RETBLEED),
+	VULNBL_INTEL_STEPPINGS(ROCKETLAKE,	X86_STEPPING_ANY,		MMIO | RETBLEED),
+	VULNBL_INTEL_STEPPINGS(ATOM_TREMONT,	X86_STEPPING_ANY,		MMIO | MMIO_SBDS),
 	VULNBL_INTEL_STEPPINGS(ATOM_TREMONT_D,	X86_STEPPING_ANY,		MMIO),
-	VULNBL_INTEL_STEPPINGS(ATOM_TREMONT_L,	X86_STEPPINGS(0x0, 0x0),	MMIO | MMIO_SBDS),
+	VULNBL_INTEL_STEPPINGS(ATOM_TREMONT_L,	X86_STEPPING_ANY,		MMIO | MMIO_SBDS),
+
+	VULNBL_AMD(0x15, RETBLEED),
+	VULNBL_AMD(0x16, RETBLEED),
+	VULNBL_AMD(0x17, RETBLEED),
+	VULNBL_HYGON(0x18, RETBLEED),
 	{}
 };

@ -1348,6 +1360,11 @@ static void __init cpu_set_bug_bits(struct cpuinfo_x86 *c)
 	    !arch_cap_mmio_immune(ia32_cap))
 		setup_force_cpu_bug(X86_BUG_MMIO_STALE_DATA);

+	if (!cpu_has(c, X86_FEATURE_BTC_NO)) {
+		if (cpu_matches(cpu_vuln_blacklist, RETBLEED) || (ia32_cap & ARCH_CAP_RSBA))
+			setup_force_cpu_bug(X86_BUG_RETBLEED);
+	}
+
 	if (cpu_matches(cpu_vuln_whitelist, NO_MELTDOWN))
 		return;

--- a/arch/x86/kernel/cpu/cpu.h
+++ b/arch/x86/kernel/cpu/cpu.h
@ -61,6 +61,8 @@ static inline void tsx_init(void) { }
 static inline void tsx_ap_init(void) { }
 #endif /* CONFIG_CPU_SUP_INTEL */

+extern void init_spectral_chicken(struct cpuinfo_x86 *c);
+
 extern void get_cpu_cap(struct cpuinfo_x86 *c);
 extern void get_cpu_address_sizes(struct cpuinfo_x86 *c);
 extern void cpu_detect_cache_sizes(struct cpuinfo_x86 *c);
--- a/arch/x86/kernel/cpu/hygon.c
+++ b/arch/x86/kernel/cpu/hygon.c
@ -302,6 +302,12 @@ static void init_hygon(struct cpuinfo_x86 *c)
 	/* get apicid instead of initial apic id from cpuid */
 	c->apicid = hard_smp_processor_id();

+	/*
+	 * XXX someone from Hygon needs to confirm this DTRT
+	 *
+	init_spectral_chicken(c);
+	 */
+
 	set_cpu_cap(c, X86_FEATURE_ZEN);
 	set_cpu_cap(c, X86_FEATURE_CPB);

--- a/arch/x86/kernel/cpu/scattered.c
+++ b/arch/x86/kernel/cpu/scattered.c
@ -27,6 +27,7 @@ static const struct cpuid_bit cpuid_bits[] = {
 	{ X86_FEATURE_APERFMPERF,       CPUID_ECX,  0, 0x00000006, 0 },
 	{ X86_FEATURE_EPB,		CPUID_ECX,  3, 0x00000006, 0 },
 	{ X86_FEATURE_INTEL_PPIN,	CPUID_EBX,  0, 0x00000007, 1 },
+	{ X86_FEATURE_RRSBA_CTRL,	CPUID_EDX,  2, 0x00000007, 2 },
 	{ X86_FEATURE_CQM_LLC,		CPUID_EDX,  1, 0x0000000f, 0 },
 	{ X86_FEATURE_CQM_OCCUP_LLC,	CPUID_EDX,  0, 0x0000000f, 1 },
 	{ X86_FEATURE_CQM_MBM_TOTAL,	CPUID_EDX,  1, 0x0000000f, 1 },
--- a/arch/x86/kernel/ftrace.c
+++ b/arch/x86/kernel/ftrace.c
@ -301,7 +301,7 @@ union ftrace_op_code_union {
 	} __attribute__((packed));
 };

-#define RET_SIZE		1 + IS_ENABLED(CONFIG_SLS)
+#define RET_SIZE		(IS_ENABLED(CONFIG_RETPOLINE) ? 5 : 1 + IS_ENABLED(CONFIG_SLS))

 static unsigned long
 create_trampoline(struct ftrace_ops *ops, unsigned int *tramp_size)
@ -357,7 +357,10 @@ create_trampoline(struct ftrace_ops *ops, unsigned int *tramp_size)
 		goto fail;

 	ip = trampoline + size;
-	memcpy(ip, retq, RET_SIZE);
+	if (cpu_feature_enabled(X86_FEATURE_RETHUNK))
+		__text_gen_insn(ip, JMP32_INSN_OPCODE, ip, &__x86_return_thunk, JMP32_INSN_SIZE);
+	else
+		memcpy(ip, retq, sizeof(retq));

 	/* No need to test direct calls on created trampolines */
 	if (ops->flags & FTRACE_OPS_FL_SAVE_REGS) {
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@ -389,6 +389,8 @@ SYM_CODE_START_NOALIGN(vc_boot_ghcb)
 	UNWIND_HINT_IRET_REGS offset=8
 	ENDBR

+	ANNOTATE_UNRET_END
+
 	/* Build pt_regs */
 	PUSH_AND_CLEAR_REGS

@ -448,6 +450,7 @@ SYM_CODE_END(early_idt_handler_array)

 SYM_CODE_START_LOCAL(early_idt_handler_common)
 	UNWIND_HINT_IRET_REGS offset=16
+	ANNOTATE_UNRET_END
 	/*
 	 * The stack is the hardware frame, an error code or zero, and the
 	 * vector number.
@ -497,6 +500,8 @@ SYM_CODE_START_NOALIGN(vc_no_ghcb)
 	UNWIND_HINT_IRET_REGS offset=8
 	ENDBR

+	ANNOTATE_UNRET_END
+
 	/* Build pt_regs */
 	PUSH_AND_CLEAR_REGS

--- a/arch/x86/kernel/module.c
+++ b/arch/x86/kernel/module.c
@ -253,7 +253,7 @@ int module_finalize(const Elf_Ehdr *hdr,
 {
 	const Elf_Shdr *s, *text = NULL, *alt = NULL, *locks = NULL,
 		*para = NULL, *orc = NULL, *orc_ip = NULL,
-		*retpolines = NULL, *ibt_endbr = NULL;
+		*retpolines = NULL, *returns = NULL, *ibt_endbr = NULL;
 	char *secstrings = (void *)hdr + sechdrs[hdr->e_shstrndx].sh_offset;

 	for (s = sechdrs; s < sechdrs + hdr->e_shnum; s++) {
@ -271,6 +271,8 @@ int module_finalize(const Elf_Ehdr *hdr,
 			orc_ip = s;
 		if (!strcmp(".retpoline_sites", secstrings + s->sh_name))
 			retpolines = s;
+		if (!strcmp(".return_sites", secstrings + s->sh_name))
+			returns = s;
 		if (!strcmp(".ibt_endbr_seal", secstrings + s->sh_name))
 			ibt_endbr = s;
 	}
@ -287,6 +289,10 @@ int module_finalize(const Elf_Ehdr *hdr,
 		void *rseg = (void *)retpolines->sh_addr;
 		apply_retpolines(rseg, rseg + retpolines->sh_size);
 	}
+	if (returns) {
+		void *rseg = (void *)returns->sh_addr;
+		apply_returns(rseg, rseg + returns->sh_size);
+	}
 	if (alt) {
 		/* patch .altinstructions */
 		void *aseg = (void *)alt->sh_addr;
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@ -600,7 +600,7 @@ static __always_inline void __speculation_ctrl_update(unsigned long tifp,
 	}

 	if (updmsr)
-		wrmsrl(MSR_IA32_SPEC_CTRL, msr);
+		write_spec_ctrl_current(msr, false);
 }

 static unsigned long speculation_ctrl_update_tif(struct task_struct *tsk)
--- a/arch/x86/kernel/relocate_kernel_32.S
+++ b/arch/x86/kernel/relocate_kernel_32.S
@ -7,10 +7,12 @@
 #include <linux/linkage.h>
 #include <asm/page_types.h>
 #include <asm/kexec.h>
+#include <asm/nospec-branch.h>
 #include <asm/processor-flags.h>

 /*
- * Must be relocatable PIC code callable as a C function
+ * Must be relocatable PIC code callable as a C function, in particular
+ * there must be a plain RET and not jump to return thunk.
 */

 #define PTR(x) (x << 2)
@ -91,7 +93,9 @@ SYM_CODE_START_NOALIGN(relocate_kernel)
 	movl    %edi, %eax
 	addl    $(identity_mapped - relocate_kernel), %eax
 	pushl   %eax
-	RET
+	ANNOTATE_UNRET_SAFE
+	ret
+	int3
 SYM_CODE_END(relocate_kernel)

 SYM_CODE_START_LOCAL_NOALIGN(identity_mapped)
@ -159,12 +163,15 @@ SYM_CODE_START_LOCAL_NOALIGN(identity_mapped)
 	xorl    %edx, %edx
 	xorl    %esi, %esi
 	xorl    %ebp, %ebp
-	RET
+	ANNOTATE_UNRET_SAFE
+	ret
+	int3
 1:
 	popl	%edx
 	movl	CP_PA_SWAP_PAGE(%edi), %esp
 	addl	$PAGE_SIZE, %esp
 2:
+	ANNOTATE_RETPOLINE_SAFE
 	call	*%edx

 	/* get the re-entry point of the peer system */
@ -190,7 +197,9 @@ SYM_CODE_START_LOCAL_NOALIGN(identity_mapped)
 	movl	%edi, %eax
 	addl	$(virtual_mapped - relocate_kernel), %eax
 	pushl	%eax
-	RET
+	ANNOTATE_UNRET_SAFE
+	ret
+	int3
 SYM_CODE_END(identity_mapped)

 SYM_CODE_START_LOCAL_NOALIGN(virtual_mapped)
@ -208,7 +217,9 @@ SYM_CODE_START_LOCAL_NOALIGN(virtual_mapped)
 	popl	%edi
 	popl	%esi
 	popl	%ebx
-	RET
+	ANNOTATE_UNRET_SAFE
+	ret
+	int3
 SYM_CODE_END(virtual_mapped)

 	/* Do the copies */
@ -271,7 +282,9 @@ SYM_CODE_START_LOCAL_NOALIGN(swap_pages)
 	popl	%edi
 	popl	%ebx
 	popl	%ebp
-	RET
+	ANNOTATE_UNRET_SAFE
+	ret
+	int3
 SYM_CODE_END(swap_pages)

 	.globl kexec_control_code_size
--- a/arch/x86/kernel/relocate_kernel_64.S
+++ b/arch/x86/kernel/relocate_kernel_64.S
@ -13,7 +13,8 @@
 #include <asm/unwind_hints.h>

 /*
- * Must be relocatable PIC code callable as a C function
+ * Must be relocatable PIC code callable as a C function, in particular
+ * there must be a plain RET and not jump to return thunk.
 */

 #define PTR(x) (x << 3)
@ -105,7 +106,9 @@ SYM_CODE_START_NOALIGN(relocate_kernel)
 	/* jump to identity mapped page */
 	addq	$(identity_mapped - relocate_kernel), %r8
 	pushq	%r8
-	RET
+	ANNOTATE_UNRET_SAFE
+	ret
+	int3
 SYM_CODE_END(relocate_kernel)

 SYM_CODE_START_LOCAL_NOALIGN(identity_mapped)
@ -200,7 +203,9 @@ SYM_CODE_START_LOCAL_NOALIGN(identity_mapped)
 	xorl	%r14d, %r14d
 	xorl	%r15d, %r15d

-	RET
+	ANNOTATE_UNRET_SAFE
+	ret
+	int3

 1:
 	popq	%rdx
@ -219,7 +224,9 @@ SYM_CODE_START_LOCAL_NOALIGN(identity_mapped)
 	call	swap_pages
 	movq	$virtual_mapped, %rax
 	pushq	%rax
-	RET
+	ANNOTATE_UNRET_SAFE
+	ret
+	int3
 SYM_CODE_END(identity_mapped)

 SYM_CODE_START_LOCAL_NOALIGN(virtual_mapped)
@ -241,7 +248,9 @@ SYM_CODE_START_LOCAL_NOALIGN(virtual_mapped)
 	popq	%r12
 	popq	%rbp
 	popq	%rbx
-	RET
+	ANNOTATE_UNRET_SAFE
+	ret
+	int3
 SYM_CODE_END(virtual_mapped)

 	/* Do the copies */
@ -298,7 +307,9 @@ SYM_CODE_START_LOCAL_NOALIGN(swap_pages)
 	lea	PAGE_SIZE(%rax), %rsi
 	jmp	0b
 3:
-	RET
+	ANNOTATE_UNRET_SAFE
+	ret
+	int3
 SYM_CODE_END(swap_pages)

 	.globl kexec_control_code_size
--- a/arch/x86/kernel/static_call.c
+++ b/arch/x86/kernel/static_call.c
@ -11,6 +11,13 @@ enum insn_type {
 	RET = 3,  /* tramp / site cond-tail-call */
 };

+/*
+ * ud1 %esp, %ecx - a 3 byte #UD that is unique to trampolines, chosen such
+ * that there is no false-positive trampoline identification while also being a
+ * speculation stop.
+ */
+static const u8 tramp_ud[] = { 0x0f, 0xb9, 0xcc };
+
 /*
 * cs cs cs xorl %eax, %eax - a single 5 byte instruction that clears %[er]ax
 */
@ -43,7 +50,10 @@ static void __ref __static_call_transform(void *insn, enum insn_type type, void
 		break;

 	case RET:
-		code = &retinsn;
+		if (cpu_feature_enabled(X86_FEATURE_RETHUNK))
+			code = text_gen_insn(JMP32_INSN_OPCODE, insn, &__x86_return_thunk);
+		else
+			code = &retinsn;
 		break;
 	}

@ -60,7 +70,7 @@ static void __static_call_validate(void *insn, bool tail, bool tramp)
 {
 	u8 opcode = *(u8 *)insn;

-	if (tramp && memcmp(insn+5, "SCT", 3)) {
+	if (tramp && memcmp(insn+5, tramp_ud, 3)) {
 		pr_err("trampoline signature fail");
 		BUG();
 	}
@ -115,3 +125,29 @@ void arch_static_call_transform(void *site, void *tramp, void *func, bool tail)
 	mutex_unlock(&text_mutex);
 }
 EXPORT_SYMBOL_GPL(arch_static_call_transform);
+
+#ifdef CONFIG_RETHUNK
+/*
+ * This is called by apply_returns() to fix up static call trampolines,
+ * specifically ARCH_DEFINE_STATIC_CALL_NULL_TRAMP which is recorded as
+ * having a return trampoline.
+ *
+ * The problem is that static_call() is available before determining
+ * X86_FEATURE_RETHUNK and, by implication, running alternatives.
+ *
+ * This means that __static_call_transform() above can have overwritten the
+ * return trampoline and we now need to fix things up to be consistent.
+ */
+bool __static_call_fixup(void *tramp, u8 op, void *dest)
+{
+	if (memcmp(tramp+5, tramp_ud, 3)) {
+		/* Not a trampoline site, not our problem. */
+		return false;
+	}
+
+	if (op == RET_INSN_OPCODE || dest == &__x86_return_thunk)
+		__static_call_transform(tramp, RET, NULL);
+
+	return true;
+}
+#endif
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@ -141,7 +141,7 @@ SECTIONS

 #ifdef CONFIG_RETPOLINE
 		__indirect_thunk_start = .;
-		*(.text.__x86.indirect_thunk)
+		*(.text.__x86.*)
 		__indirect_thunk_end = .;
 #endif
 	} :text =0xcccc
@ -283,6 +283,13 @@ SECTIONS
 		*(.retpoline_sites)
 		__retpoline_sites_end = .;
 	}
+
+	. = ALIGN(8);
+	.return_sites : AT(ADDR(.return_sites) - LOAD_OFFSET) {
+		__return_sites = .;
+		*(.return_sites)
+		__return_sites_end = .;
+	}
 #endif

 #ifdef CONFIG_X86_KERNEL_IBT
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@ -325,13 +325,15 @@ static int fastop(struct x86_emulate_ctxt *ctxt, fastop_t fop);
 #define FOP_RET(name) \
 	__FOP_RET(#name)

-#define FOP_START(op) \
+#define __FOP_START(op, align) \
 	extern void em_##op(struct fastop *fake); \
 	asm(".pushsection .text, \"ax\" \n\t" \
 	    ".global em_" #op " \n\t" \
-	    ".align " __stringify(FASTOP_SIZE) " \n\t" \
+	    ".align " __stringify(align) " \n\t" \
 	    "em_" #op ":\n\t"

+#define FOP_START(op) __FOP_START(op, FASTOP_SIZE)
+
 #define FOP_END \
 	    ".popsection")

@ -435,16 +437,15 @@ static int fastop(struct x86_emulate_ctxt *ctxt, fastop_t fop);
 /*
 * Depending on .config the SETcc functions look like:
 *
- * ENDBR       [4 bytes; CONFIG_X86_KERNEL_IBT]
- * SETcc %al   [3 bytes]
- * RET         [1 byte]
- * INT3        [1 byte; CONFIG_SLS]
- *
- * Which gives possible sizes 4, 5, 8 or 9.  When rounded up to the
- * next power-of-two alignment they become 4, 8 or 16 resp.
+ * ENDBR			[4 bytes; CONFIG_X86_KERNEL_IBT]
+ * SETcc %al			[3 bytes]
+ * RET | JMP __x86_return_thunk	[1,5 bytes; CONFIG_RETHUNK]
+ * INT3				[1 byte; CONFIG_SLS]
 */
-#define SETCC_LENGTH	(ENDBR_INSN_SIZE + 4 + IS_ENABLED(CONFIG_SLS))
-#define SETCC_ALIGN	(4 << IS_ENABLED(CONFIG_SLS) << HAS_KERNEL_IBT)
+#define RET_LENGTH	(1 + (4 * IS_ENABLED(CONFIG_RETHUNK)) + \
+			 IS_ENABLED(CONFIG_SLS))
+#define SETCC_LENGTH	(ENDBR_INSN_SIZE + 3 + RET_LENGTH)
+#define SETCC_ALIGN	(4 << ((SETCC_LENGTH > 4) & 1) << ((SETCC_LENGTH > 8) & 1))
 static_assert(SETCC_LENGTH <= SETCC_ALIGN);

 #define FOP_SETCC(op) \
@ -453,9 +454,10 @@ static_assert(SETCC_LENGTH <= SETCC_ALIGN);
 	#op ": \n\t" \
 	ASM_ENDBR \
 	#op " %al \n\t" \
-	__FOP_RET(#op)
+	__FOP_RET(#op) \
+	".skip " __stringify(SETCC_ALIGN) " - (.-" #op "), 0xcc \n\t"

-FOP_START(setcc)
+__FOP_START(setcc, SETCC_ALIGN)
 FOP_SETCC(seto)
 FOP_SETCC(setno)
 FOP_SETCC(setc)
--- a/arch/x86/kvm/svm/vmenter.S
+++ b/arch/x86/kvm/svm/vmenter.S
@ -110,6 +110,15 @@ SYM_FUNC_START(__svm_vcpu_run)
 	mov %r15, VCPU_R15(%_ASM_AX)
 #endif

+	/*
+	 * Mitigate RETBleed for AMD/Hygon Zen uarch. RET should be
+	 * untrained as soon as we exit the VM and are back to the
+	 * kernel. This should be done before re-enabling interrupts
+	 * because interrupt handlers won't sanitize 'ret' if the return is
+	 * from the kernel.
+	 */
+	UNTRAIN_RET
+
 	/*
 	 * Clear all general purpose registers except RSP and RAX to prevent
 	 * speculative use of the guest's values, even those that are reloaded
@ -190,6 +199,15 @@ SYM_FUNC_START(__svm_sev_es_vcpu_run)
 	FILL_RETURN_BUFFER %_ASM_AX, RSB_CLEAR_LOOPS, X86_FEATURE_RETPOLINE
 #endif

+	/*
+	 * Mitigate RETBleed for AMD/Hygon Zen uarch. RET should be
+	 * untrained as soon as we exit the VM and are back to the
+	 * kernel. This should be done before re-enabling interrupts
+	 * because interrupt handlers won't sanitize RET if the return is
+	 * from the kernel.
+	 */
+	UNTRAIN_RET
+
 	pop %_ASM_BX

 #ifdef CONFIG_X86_64
--- a/arch/x86/kvm/vmx/capabilities.h
+++ b/arch/x86/kvm/vmx/capabilities.h
@ -4,8 +4,8 @@

 #include <asm/vmx.h>

-#include "lapic.h"
-#include "x86.h"
+#include "../lapic.h"
+#include "../x86.h"

 extern bool __read_mostly enable_vpid;
 extern bool __read_mostly flexpriority_enabled;
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@ -3087,7 +3087,7 @@ static int nested_vmx_check_vmentry_hw(struct kvm_vcpu *vcpu)
 	}

 	vm_fail = __vmx_vcpu_run(vmx, (unsigned long *)&vcpu->arch.regs,
-				 vmx->loaded_vmcs->launched);
+				 __vmx_vcpu_run_flags(vmx));

 	if (vmx->msr_autoload.host.nr)
 		vmcs_write32(VM_EXIT_MSR_LOAD_COUNT, vmx->msr_autoload.host.nr);
--- a/arch/x86/kvm/vmx/run_flags.h
+++ b/arch/x86/kvm/vmx/run_flags.h
@ -0,0 +1,8 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __KVM_X86_VMX_RUN_FLAGS_H
+#define __KVM_X86_VMX_RUN_FLAGS_H
+
+#define VMX_RUN_VMRESUME	(1 << 0)
+#define VMX_RUN_SAVE_SPEC_CTRL	(1 << 1)
+
+#endif /* __KVM_X86_VMX_RUN_FLAGS_H */
--- a/arch/x86/kvm/vmx/vmenter.S
+++ b/arch/x86/kvm/vmx/vmenter.S
@ -1,10 +1,13 @@
 /* SPDX-License-Identifier: GPL-2.0 */
 #include <linux/linkage.h>
 #include <asm/asm.h>
+#include <asm/asm-offsets.h>
 #include <asm/bitsperlong.h>
 #include <asm/kvm_vcpu_regs.h>
 #include <asm/nospec-branch.h>
+#include <asm/percpu.h>
 #include <asm/segment.h>
+#include "run_flags.h"

 #define WORD_SIZE (BITS_PER_LONG / 8)

@ -30,73 +33,12 @@

 .section .noinstr.text, "ax"

-/**
- * vmx_vmenter - VM-Enter the current loaded VMCS
- *
- * %RFLAGS.ZF:	!VMCS.LAUNCHED, i.e. controls VMLAUNCH vs. VMRESUME
- *
- * Returns:
- *	%RFLAGS.CF is set on VM-Fail Invalid
- *	%RFLAGS.ZF is set on VM-Fail Valid
- *	%RFLAGS.{CF,ZF} are cleared on VM-Success, i.e. VM-Exit
- *
- * Note that VMRESUME/VMLAUNCH fall-through and return directly if
- * they VM-Fail, whereas a successful VM-Enter + VM-Exit will jump
- * to vmx_vmexit.
- */
-SYM_FUNC_START_LOCAL(vmx_vmenter)
-	/* EFLAGS.ZF is set if VMCS.LAUNCHED == 0 */
-	je 2f
-
-1:	vmresume
-	RET
-
-2:	vmlaunch
-	RET
-
-3:	cmpb $0, kvm_rebooting
-	je 4f
-	RET
-4:	ud2
-
-	_ASM_EXTABLE(1b, 3b)
-	_ASM_EXTABLE(2b, 3b)
-
-SYM_FUNC_END(vmx_vmenter)
-
-/**
- * vmx_vmexit - Handle a VMX VM-Exit
- *
- * Returns:
- *	%RFLAGS.{CF,ZF} are cleared on VM-Success, i.e. VM-Exit
- *
- * This is vmx_vmenter's partner in crime.  On a VM-Exit, control will jump
- * here after hardware loads the host's state, i.e. this is the destination
- * referred to by VMCS.HOST_RIP.
- */
-SYM_FUNC_START(vmx_vmexit)
-#ifdef CONFIG_RETPOLINE
-	ALTERNATIVE "jmp .Lvmexit_skip_rsb", "", X86_FEATURE_RETPOLINE
-	/* Preserve guest's RAX, it's used to stuff the RSB. */
-	push %_ASM_AX
-
-	/* IMPORTANT: Stuff the RSB immediately after VM-Exit, before RET! */
-	FILL_RETURN_BUFFER %_ASM_AX, RSB_CLEAR_LOOPS, X86_FEATURE_RETPOLINE
-
-	/* Clear RFLAGS.CF and RFLAGS.ZF to preserve VM-Exit, i.e. !VM-Fail. */
-	or $1, %_ASM_AX
-
-	pop %_ASM_AX
-.Lvmexit_skip_rsb:
-#endif
-	RET
-SYM_FUNC_END(vmx_vmexit)
-
 /**
 * __vmx_vcpu_run - Run a vCPU via a transition to VMX guest mode
- * @vmx:	struct vcpu_vmx * (forwarded to vmx_update_host_rsp)
+ * @vmx:	struct vcpu_vmx *
 * @regs:	unsigned long * (to guest registers)
- * @launched:	%true if the VMCS has been launched
+ * @flags:	VMX_RUN_VMRESUME:	use VMRESUME instead of VMLAUNCH
+ *		VMX_RUN_SAVE_SPEC_CTRL: save guest SPEC_CTRL into vmx->spec_ctrl
 *
 * Returns:
 *	0 on VM-Exit, 1 on VM-Fail
@ -115,24 +57,56 @@ SYM_FUNC_START(__vmx_vcpu_run)
 #endif
 	push %_ASM_BX

+	/* Save @vmx for SPEC_CTRL handling */
+	push %_ASM_ARG1
+
+	/* Save @flags for SPEC_CTRL handling */
+	push %_ASM_ARG3
+
 	/*
 	 * Save @regs, _ASM_ARG2 may be modified by vmx_update_host_rsp() and
 	 * @regs is needed after VM-Exit to save the guest's register values.
 	 */
 	push %_ASM_ARG2

-	/* Copy @launched to BL, _ASM_ARG3 is volatile. */
+	/* Copy @flags to BL, _ASM_ARG3 is volatile. */
 	mov %_ASM_ARG3B, %bl

-	/* Adjust RSP to account for the CALL to vmx_vmenter(). */
-	lea -WORD_SIZE(%_ASM_SP), %_ASM_ARG2
+	lea (%_ASM_SP), %_ASM_ARG2
 	call vmx_update_host_rsp

+	ALTERNATIVE "jmp .Lspec_ctrl_done", "", X86_FEATURE_MSR_SPEC_CTRL
+
+	/*
+	 * SPEC_CTRL handling: if the guest's SPEC_CTRL value differs from the
+	 * host's, write the MSR.
+	 *
+	 * IMPORTANT: To avoid RSB underflow attacks and any other nastiness,
+	 * there must not be any returns or indirect branches between this code
+	 * and vmentry.
+	 */
+	mov 2*WORD_SIZE(%_ASM_SP), %_ASM_DI
+	movl VMX_spec_ctrl(%_ASM_DI), %edi
+	movl PER_CPU_VAR(x86_spec_ctrl_current), %esi
+	cmp %edi, %esi
+	je .Lspec_ctrl_done
+	mov $MSR_IA32_SPEC_CTRL, %ecx
+	xor %edx, %edx
+	mov %edi, %eax
+	wrmsr
+
+.Lspec_ctrl_done:
+
+	/*
+	 * Since vmentry is serializing on affected CPUs, there's no need for
+	 * an LFENCE to stop speculation from skipping the wrmsr.
+	 */
+
 	/* Load @regs to RAX. */
 	mov (%_ASM_SP), %_ASM_AX

 	/* Check if vmlaunch or vmresume is needed */
-	testb %bl, %bl
+	testb $VMX_RUN_VMRESUME, %bl

 	/* Load guest registers.  Don't clobber flags. */
 	mov VCPU_RCX(%_ASM_AX), %_ASM_CX
@ -154,11 +128,37 @@ SYM_FUNC_START(__vmx_vcpu_run)
 	/* Load guest RAX.  This kills the @regs pointer! */
 	mov VCPU_RAX(%_ASM_AX), %_ASM_AX

-	/* Enter guest mode */
-	call vmx_vmenter
+	/* Check EFLAGS.ZF from 'testb' above */
+	jz .Lvmlaunch

-	/* Jump on VM-Fail. */
-	jbe 2f
+	/*
+	 * After a successful VMRESUME/VMLAUNCH, control flow "magically"
+	 * resumes below at 'vmx_vmexit' due to the VMCS HOST_RIP setting.
+	 * So this isn't a typical function and objtool needs to be told to
+	 * save the unwind state here and restore it below.
+	 */
+	UNWIND_HINT_SAVE
+
+/*
+ * If VMRESUME/VMLAUNCH and corresponding vmexit succeed, execution resumes at
+ * the 'vmx_vmexit' label below.
+ */
+.Lvmresume:
+	vmresume
+	jmp .Lvmfail
+
+.Lvmlaunch:
+	vmlaunch
+	jmp .Lvmfail
+
+	_ASM_EXTABLE(.Lvmresume, .Lfixup)
+	_ASM_EXTABLE(.Lvmlaunch, .Lfixup)
+
+SYM_INNER_LABEL(vmx_vmexit, SYM_L_GLOBAL)
+
+	/* Restore unwind state from before the VMRESUME/VMLAUNCH. */
+	UNWIND_HINT_RESTORE
+	ENDBR

 	/* Temporarily save guest's RAX. */
 	push %_ASM_AX
@ -185,21 +185,23 @@ SYM_FUNC_START(__vmx_vcpu_run)
 	mov %r15, VCPU_R15(%_ASM_AX)
 #endif

-	/* Clear RAX to indicate VM-Exit (as opposed to VM-Fail). */
-	xor %eax, %eax
+	/* Clear return value to indicate VM-Exit (as opposed to VM-Fail). */
+	xor %ebx, %ebx

+.Lclear_regs:
 	/*
-	 * Clear all general purpose registers except RSP and RAX to prevent
+	 * Clear all general purpose registers except RSP and RBX to prevent
 	 * speculative use of the guest's values, even those that are reloaded
 	 * via the stack.  In theory, an L1 cache miss when restoring registers
 	 * could lead to speculative execution with the guest's values.
 	 * Zeroing XORs are dirt cheap, i.e. the extra paranoia is essentially
 	 * free.  RSP and RAX are exempt as RSP is restored by hardware during
-	 * VM-Exit and RAX is explicitly loaded with 0 or 1 to return VM-Fail.
+	 * VM-Exit and RBX is explicitly loaded with 0 or 1 to hold the return
+	 * value.
 	 */
-1:	xor %ecx, %ecx
+	xor %eax, %eax
+	xor %ecx, %ecx
 	xor %edx, %edx
-	xor %ebx, %ebx
 	xor %ebp, %ebp
 	xor %esi, %esi
 	xor %edi, %edi
@ -216,8 +218,30 @@ SYM_FUNC_START(__vmx_vcpu_run)

 	/* "POP" @regs. */
 	add $WORD_SIZE, %_ASM_SP
-	pop %_ASM_BX

+	/*
+	 * IMPORTANT: RSB filling and SPEC_CTRL handling must be done before
+	 * the first unbalanced RET after vmexit!
+	 *
+	 * For retpoline or IBRS, RSB filling is needed to prevent poisoned RSB
+	 * entries and (in some cases) RSB underflow.
+	 *
+	 * eIBRS has its own protection against poisoned RSB, so it doesn't
+	 * need the RSB filling sequence.  But it does need to be enabled
+	 * before the first unbalanced RET.
+         */
+
+	FILL_RETURN_BUFFER %_ASM_CX, RSB_CLEAR_LOOPS, X86_FEATURE_RSB_VMEXIT
+
+	pop %_ASM_ARG2	/* @flags */
+	pop %_ASM_ARG1	/* @vmx */
+
+	call vmx_spec_ctrl_restore_host
+
+	/* Put return value in AX */
+	mov %_ASM_BX, %_ASM_AX
+
+	pop %_ASM_BX
 #ifdef CONFIG_X86_64
 	pop %r12
 	pop %r13
@ -230,9 +254,15 @@ SYM_FUNC_START(__vmx_vcpu_run)
 	pop %_ASM_BP
 	RET

-	/* VM-Fail.  Out-of-line to avoid a taken Jcc after VM-Exit. */
-2:	mov $1, %eax
-	jmp 1b
+.Lfixup:
+	cmpb $0, kvm_rebooting
+	jne .Lvmfail
+	ud2
+.Lvmfail:
+	/* VM-Fail: set return value to 1 */
+	mov $1, %_ASM_BX
+	jmp .Lclear_regs
+
 SYM_FUNC_END(__vmx_vcpu_run)


--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@ -383,9 +383,9 @@ static __always_inline void vmx_disable_fb_clear(struct vcpu_vmx *vmx)
 	if (!vmx->disable_fb_clear)
 		return;

-	rdmsrl(MSR_IA32_MCU_OPT_CTRL, msr);
+	msr = __rdmsr(MSR_IA32_MCU_OPT_CTRL);
 	msr |= FB_CLEAR_DIS;
-	wrmsrl(MSR_IA32_MCU_OPT_CTRL, msr);
+	native_wrmsrl(MSR_IA32_MCU_OPT_CTRL, msr);
 	/* Cache the MSR value to avoid reading it later */
 	vmx->msr_ia32_mcu_opt_ctrl = msr;
 }
@ -396,7 +396,7 @@ static __always_inline void vmx_enable_fb_clear(struct vcpu_vmx *vmx)
 		return;

 	vmx->msr_ia32_mcu_opt_ctrl &= ~FB_CLEAR_DIS;
-	wrmsrl(MSR_IA32_MCU_OPT_CTRL, vmx->msr_ia32_mcu_opt_ctrl);
+	native_wrmsrl(MSR_IA32_MCU_OPT_CTRL, vmx->msr_ia32_mcu_opt_ctrl);
 }

 static void vmx_update_fb_clear_dis(struct kvm_vcpu *vcpu, struct vcpu_vmx *vmx)
@ -839,6 +839,24 @@ static bool msr_write_intercepted(struct vcpu_vmx *vmx, u32 msr)
 					 MSR_IA32_SPEC_CTRL);
 }

+unsigned int __vmx_vcpu_run_flags(struct vcpu_vmx *vmx)
+{
+	unsigned int flags = 0;
+
+	if (vmx->loaded_vmcs->launched)
+		flags |= VMX_RUN_VMRESUME;
+
+	/*
+	 * If writes to the SPEC_CTRL MSR aren't intercepted, the guest is free
+	 * to change it directly without causing a vmexit.  In that case read
+	 * it after vmexit and store it in vmx->spec_ctrl.
+	 */
+	if (unlikely(!msr_write_intercepted(vmx, MSR_IA32_SPEC_CTRL)))
+		flags |= VMX_RUN_SAVE_SPEC_CTRL;
+
+	return flags;
+}
+
 static void clear_atomic_switch_msr_special(struct vcpu_vmx *vmx,
 		unsigned long entry, unsigned long exit)
 {
@ -6813,6 +6831,31 @@ void noinstr vmx_update_host_rsp(struct vcpu_vmx *vmx, unsigned long host_rsp)
 	}
 }

+void noinstr vmx_spec_ctrl_restore_host(struct vcpu_vmx *vmx,
+					unsigned int flags)
+{
+	u64 hostval = this_cpu_read(x86_spec_ctrl_current);
+
+	if (!cpu_feature_enabled(X86_FEATURE_MSR_SPEC_CTRL))
+		return;
+
+	if (flags & VMX_RUN_SAVE_SPEC_CTRL)
+		vmx->spec_ctrl = __rdmsr(MSR_IA32_SPEC_CTRL);
+
+	/*
+	 * If the guest/host SPEC_CTRL values differ, restore the host value.
+	 *
+	 * For legacy IBRS, the IBRS bit always needs to be written after
+	 * transitioning from a less privileged predictor mode, regardless of
+	 * whether the guest/host values differ.
+	 */
+	if (cpu_feature_enabled(X86_FEATURE_KERNEL_IBRS) ||
+	    vmx->spec_ctrl != hostval)
+		native_wrmsrl(MSR_IA32_SPEC_CTRL, hostval);
+
+	barrier_nospec();
+}
+
 static fastpath_t vmx_exit_handlers_fastpath(struct kvm_vcpu *vcpu)
 {
 	switch (to_vmx(vcpu)->exit_reason.basic) {
@ -6826,7 +6869,8 @@ static fastpath_t vmx_exit_handlers_fastpath(struct kvm_vcpu *vcpu)
 }

 static noinstr void vmx_vcpu_enter_exit(struct kvm_vcpu *vcpu,
-					struct vcpu_vmx *vmx)
+					struct vcpu_vmx *vmx,
+					unsigned long flags)
 {
 	guest_state_enter_irqoff();

@ -6845,7 +6889,7 @@ static noinstr void vmx_vcpu_enter_exit(struct kvm_vcpu *vcpu,
 		native_write_cr2(vcpu->arch.cr2);

 	vmx->fail = __vmx_vcpu_run(vmx, (unsigned long *)&vcpu->arch.regs,
-				   vmx->loaded_vmcs->launched);
+				   flags);

 	vcpu->arch.cr2 = native_read_cr2();

@ -6944,36 +6988,8 @@ static fastpath_t vmx_vcpu_run(struct kvm_vcpu *vcpu)

 	kvm_wait_lapic_expire(vcpu);

-	/*
-	 * If this vCPU has touched SPEC_CTRL, restore the guest's value if
-	 * it's non-zero. Since vmentry is serialising on affected CPUs, there
-	 * is no need to worry about the conditional branch over the wrmsr
-	 * being speculatively taken.
-	 */
-	x86_spec_ctrl_set_guest(vmx->spec_ctrl, 0);
-
 	/* The actual VMENTER/EXIT is in the .noinstr.text section. */
-	vmx_vcpu_enter_exit(vcpu, vmx);
-
-	/*
-	 * We do not use IBRS in the kernel. If this vCPU has used the
-	 * SPEC_CTRL MSR it may have left it on; save the value and
-	 * turn it off. This is much more efficient than blindly adding
-	 * it to the atomic save/restore list. Especially as the former
-	 * (Saving guest MSRs on vmexit) doesn't even exist in KVM.
-	 *
-	 * For non-nested case:
-	 * If the L01 MSR bitmap does not intercept the MSR, then we need to
-	 * save it.
-	 *
-	 * For nested case:
-	 * If the L02 MSR bitmap does not intercept the MSR, then we need to
-	 * save it.
-	 */
-	if (unlikely(!msr_write_intercepted(vmx, MSR_IA32_SPEC_CTRL)))
-		vmx->spec_ctrl = native_read_msr(MSR_IA32_SPEC_CTRL);
-
-	x86_spec_ctrl_restore_host(vmx->spec_ctrl, 0);
+	vmx_vcpu_enter_exit(vcpu, vmx, __vmx_vcpu_run_flags(vmx));

 	/* All fields are clean at this point */
 	if (static_branch_unlikely(&enable_evmcs)) {
--- a/arch/x86/kvm/vmx/vmx.h
+++ b/arch/x86/kvm/vmx/vmx.h
@ -8,11 +8,12 @@
 #include <asm/intel_pt.h>

 #include "capabilities.h"
-#include "kvm_cache_regs.h"
+#include "../kvm_cache_regs.h"
 #include "posted_intr.h"
 #include "vmcs.h"
 #include "vmx_ops.h"
-#include "cpuid.h"
+#include "../cpuid.h"
+#include "run_flags.h"

 #define MSR_TYPE_R	1
 #define MSR_TYPE_W	2
@ -404,7 +405,10 @@ void vmx_set_virtual_apic_mode(struct kvm_vcpu *vcpu);
 struct vmx_uret_msr *vmx_find_uret_msr(struct vcpu_vmx *vmx, u32 msr);
 void pt_update_intercept_for_msr(struct kvm_vcpu *vcpu);
 void vmx_update_host_rsp(struct vcpu_vmx *vmx, unsigned long host_rsp);
-bool __vmx_vcpu_run(struct vcpu_vmx *vmx, unsigned long *regs, bool launched);
+void vmx_spec_ctrl_restore_host(struct vcpu_vmx *vmx, unsigned int flags);
+unsigned int __vmx_vcpu_run_flags(struct vcpu_vmx *vmx);
+bool __vmx_vcpu_run(struct vcpu_vmx *vmx, unsigned long *regs,
+		    unsigned int flags);
 int vmx_find_loadstore_msr_slot(struct vmx_msrs *m, u32 msr);
 void vmx_ept_load_pdptrs(struct kvm_vcpu *vcpu);

--- a/arch/x86/kvm/vmx/vmx_ops.h
+++ b/arch/x86/kvm/vmx/vmx_ops.h
@ -8,7 +8,7 @@

 #include "evmcs.h"
 #include "vmcs.h"
-#include "x86.h"
+#include "../x86.h"

 asmlinkage void vmread_error(unsigned long field, bool fault);
 __attribute__((regparm(0))) void vmread_error_trampoline(unsigned long field,
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@ -12631,9 +12631,9 @@ void kvm_arch_end_assignment(struct kvm *kvm)
 }
 EXPORT_SYMBOL_GPL(kvm_arch_end_assignment);

-bool kvm_arch_has_assigned_device(struct kvm *kvm)
+bool noinstr kvm_arch_has_assigned_device(struct kvm *kvm)
 {
-	return atomic_read(&kvm->arch.assigned_device_count);
+	return arch_atomic_read(&kvm->arch.assigned_device_count);
 }
 EXPORT_SYMBOL_GPL(kvm_arch_has_assigned_device);

--- a/arch/x86/lib/memmove_64.S
+++ b/arch/x86/lib/memmove_64.S
@ -39,7 +39,7 @@ SYM_FUNC_START(__memmove)
 	/* FSRM implies ERMS => no length checks, do the copy directly */
 .Lmemmove_begin_forward:
 	ALTERNATIVE "cmp $0x20, %rdx; jb 1f", "", X86_FEATURE_FSRM
-	ALTERNATIVE "", __stringify(movq %rdx, %rcx; rep movsb; RET), X86_FEATURE_ERMS
+	ALTERNATIVE "", "jmp .Lmemmove_erms", X86_FEATURE_ERMS

 	/*
 	 * movsq instruction have many startup latency
@ -205,6 +205,11 @@ SYM_FUNC_START(__memmove)
 	movb %r11b, (%rdi)
 13:
 	RET
+
+.Lmemmove_erms:
+	movq %rdx, %rcx
+	rep movsb
+	RET
 SYM_FUNC_END(__memmove)
 EXPORT_SYMBOL(__memmove)

--- a/arch/x86/lib/retpoline.S
+++ b/arch/x86/lib/retpoline.S
@ -33,9 +33,9 @@ SYM_INNER_LABEL(__x86_indirect_thunk_\reg, SYM_L_GLOBAL)
 	UNWIND_HINT_EMPTY
 	ANNOTATE_NOENDBR

-	ALTERNATIVE_2 __stringify(ANNOTATE_RETPOLINE_SAFE; jmp *%\reg), \
-		      __stringify(RETPOLINE \reg), X86_FEATURE_RETPOLINE, \
-		      __stringify(lfence; ANNOTATE_RETPOLINE_SAFE; jmp *%\reg; int3), X86_FEATURE_RETPOLINE_LFENCE
+	ALTERNATIVE_2 __stringify(RETPOLINE \reg), \
+		      __stringify(lfence; ANNOTATE_RETPOLINE_SAFE; jmp *%\reg; int3), X86_FEATURE_RETPOLINE_LFENCE, \
+		      __stringify(ANNOTATE_RETPOLINE_SAFE; jmp *%\reg), ALT_NOT(X86_FEATURE_RETPOLINE)

 .endm

@ -67,3 +67,76 @@ SYM_CODE_END(__x86_indirect_thunk_array)
 #define GEN(reg) EXPORT_THUNK(reg)
 #include <asm/GEN-for-each-reg.h>
 #undef GEN
+
+/*
+ * This function name is magical and is used by -mfunction-return=thunk-extern
+ * for the compiler to generate JMPs to it.
+ */
+#ifdef CONFIG_RETHUNK
+
+	.section .text.__x86.return_thunk
+
+/*
+ * Safety details here pertain to the AMD Zen{1,2} microarchitecture:
+ * 1) The RET at __x86_return_thunk must be on a 64 byte boundary, for
+ *    alignment within the BTB.
+ * 2) The instruction at zen_untrain_ret must contain, and not
+ *    end with, the 0xc3 byte of the RET.
+ * 3) STIBP must be enabled, or SMT disabled, to prevent the sibling thread
+ *    from re-poisioning the BTB prediction.
+ */
+	.align 64
+	.skip 63, 0xcc
+SYM_FUNC_START_NOALIGN(zen_untrain_ret);
+
+	/*
+	 * As executed from zen_untrain_ret, this is:
+	 *
+	 *   TEST $0xcc, %bl
+	 *   LFENCE
+	 *   JMP __x86_return_thunk
+	 *
+	 * Executing the TEST instruction has a side effect of evicting any BTB
+	 * prediction (potentially attacker controlled) attached to the RET, as
+	 * __x86_return_thunk + 1 isn't an instruction boundary at the moment.
+	 */
+	.byte	0xf6
+
+	/*
+	 * As executed from __x86_return_thunk, this is a plain RET.
+	 *
+	 * As part of the TEST above, RET is the ModRM byte, and INT3 the imm8.
+	 *
+	 * We subsequently jump backwards and architecturally execute the RET.
+	 * This creates a correct BTB prediction (type=ret), but in the
+	 * meantime we suffer Straight Line Speculation (because the type was
+	 * no branch) which is halted by the INT3.
+	 *
+	 * With SMT enabled and STIBP active, a sibling thread cannot poison
+	 * RET's prediction to a type of its choice, but can evict the
+	 * prediction due to competitive sharing. If the prediction is
+	 * evicted, __x86_return_thunk will suffer Straight Line Speculation
+	 * which will be contained safely by the INT3.
+	 */
+SYM_INNER_LABEL(__x86_return_thunk, SYM_L_GLOBAL)
+	ret
+	int3
+SYM_CODE_END(__x86_return_thunk)
+
+	/*
+	 * Ensure the TEST decoding / BTB invalidation is complete.
+	 */
+	lfence
+
+	/*
+	 * Jump back and execute the RET in the middle of the TEST instruction.
+	 * INT3 is for SLS protection.
+	 */
+	jmp __x86_return_thunk
+	int3
+SYM_FUNC_END(zen_untrain_ret)
+__EXPORT_THUNK(zen_untrain_ret)
+
+EXPORT_SYMBOL(__x86_return_thunk)
+
+#endif /* CONFIG_RETHUNK */
--- a/arch/x86/mm/mem_encrypt_boot.S
+++ b/arch/x86/mm/mem_encrypt_boot.S
@ -65,7 +65,10 @@ SYM_FUNC_START(sme_encrypt_execute)
 	movq	%rbp, %rsp		/* Restore original stack pointer */
 	pop	%rbp

-	RET
+	/* Offset to __x86_return_thunk would be wrong here */
+	ANNOTATE_UNRET_SAFE
+	ret
+	int3
 SYM_FUNC_END(sme_encrypt_execute)

 SYM_FUNC_START(__enc_copy)
@ -151,6 +154,9 @@ SYM_FUNC_START(__enc_copy)
 	pop	%r12
 	pop	%r15

-	RET
+	/* Offset to __x86_return_thunk would be wrong here */
+	ANNOTATE_UNRET_SAFE
+	ret
+	int3
 .L__enc_copy_end:
 SYM_FUNC_END(__enc_copy)
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@ -412,16 +412,30 @@ static void emit_indirect_jump(u8 **pprog, int reg, u8 *ip)
 {
 	u8 *prog = *pprog;

-#ifdef CONFIG_RETPOLINE
 	if (cpu_feature_enabled(X86_FEATURE_RETPOLINE_LFENCE)) {
 		EMIT_LFENCE();
 		EMIT2(0xFF, 0xE0 + reg);
 	} else if (cpu_feature_enabled(X86_FEATURE_RETPOLINE)) {
 		OPTIMIZER_HIDE_VAR(reg);
 		emit_jump(&prog, &__x86_indirect_thunk_array[reg], ip);
-	} else
-#endif
-	EMIT2(0xFF, 0xE0 + reg);
+	} else {
+		EMIT2(0xFF, 0xE0 + reg);
+	}
+
+	*pprog = prog;
+}
+
+static void emit_return(u8 **pprog, u8 *ip)
+{
+	u8 *prog = *pprog;
+
+	if (cpu_feature_enabled(X86_FEATURE_RETHUNK)) {
+		emit_jump(&prog, &__x86_return_thunk, ip);
+	} else {
+		EMIT1(0xC3);		/* ret */
+		if (IS_ENABLED(CONFIG_SLS))
+			EMIT1(0xCC);	/* int3 */
+	}

 	*pprog = prog;
 }
@ -1686,7 +1700,7 @@ emit_jmp:
 			ctx->cleanup_addr = proglen;
 			pop_callee_regs(&prog, callee_regs_used);
 			EMIT1(0xC9);         /* leave */
-			EMIT1(0xC3);         /* ret */
+			emit_return(&prog, image + addrs[i - 1] + (prog - temp));
 			break;

 		default:
@ -2189,7 +2203,7 @@ int arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *image, void *i
 	if (flags & BPF_TRAMP_F_SKIP_FRAME)
 		/* skip our return address and return to parent */
 		EMIT4(0x48, 0x83, 0xC4, 8); /* add rsp, 8 */
-	EMIT1(0xC3); /* ret */
+	emit_return(&prog, prog);
 	/* Make sure the trampoline generation logic doesn't overflow */
 	if (WARN_ON_ONCE(prog > (u8 *)image_end - BPF_INSN_SAFETY)) {
 		ret = -EFAULT;
--- a/arch/x86/xen/setup.c
+++ b/arch/x86/xen/setup.c
@ -918,7 +918,7 @@ void xen_enable_sysenter(void)
 	if (!boot_cpu_has(sysenter_feature))
 		return;

-	ret = register_callback(CALLBACKTYPE_sysenter, xen_sysenter_target);
+	ret = register_callback(CALLBACKTYPE_sysenter, xen_entry_SYSENTER_compat);
 	if(ret != 0)
 		setup_clear_cpu_cap(sysenter_feature);
 }
@ -927,7 +927,7 @@ void xen_enable_syscall(void)
 {
 	int ret;

-	ret = register_callback(CALLBACKTYPE_syscall, xen_syscall_target);
+	ret = register_callback(CALLBACKTYPE_syscall, xen_entry_SYSCALL_64);
 	if (ret != 0) {
 		printk(KERN_ERR "Failed to set syscall callback: %d\n", ret);
 		/* Pretty fatal; 64-bit userspace has no other
@ -936,7 +936,7 @@ void xen_enable_syscall(void)

 	if (boot_cpu_has(X86_FEATURE_SYSCALL32)) {
 		ret = register_callback(CALLBACKTYPE_syscall32,
-					xen_syscall32_target);
+					xen_entry_SYSCALL_compat);
 		if (ret != 0)
 			setup_clear_cpu_cap(X86_FEATURE_SYSCALL32);
 	}
--- a/arch/x86/xen/xen-asm.S
+++ b/arch/x86/xen/xen-asm.S
@ -121,7 +121,7 @@ SYM_FUNC_END(xen_read_cr2_direct);

 .macro xen_pv_trap name
 SYM_CODE_START(xen_\name)
-	UNWIND_HINT_EMPTY
+	UNWIND_HINT_ENTRY
 	ENDBR
 	pop %rcx
 	pop %r11
@ -234,8 +234,8 @@ SYM_CODE_END(xenpv_restore_regs_and_return_to_usermode)
 */

 /* Normal 64-bit system call target */
-SYM_CODE_START(xen_syscall_target)
-	UNWIND_HINT_EMPTY
+SYM_CODE_START(xen_entry_SYSCALL_64)
+	UNWIND_HINT_ENTRY
 	ENDBR
 	popq %rcx
 	popq %r11
@ -249,13 +249,13 @@ SYM_CODE_START(xen_syscall_target)
 	movq $__USER_CS, 1*8(%rsp)

 	jmp entry_SYSCALL_64_after_hwframe
-SYM_CODE_END(xen_syscall_target)
+SYM_CODE_END(xen_entry_SYSCALL_64)

 #ifdef CONFIG_IA32_EMULATION

 /* 32-bit compat syscall target */
-SYM_CODE_START(xen_syscall32_target)
-	UNWIND_HINT_EMPTY
+SYM_CODE_START(xen_entry_SYSCALL_compat)
+	UNWIND_HINT_ENTRY
 	ENDBR
 	popq %rcx
 	popq %r11
@ -269,11 +269,11 @@ SYM_CODE_START(xen_syscall32_target)
 	movq $__USER32_CS, 1*8(%rsp)

 	jmp entry_SYSCALL_compat_after_hwframe
-SYM_CODE_END(xen_syscall32_target)
+SYM_CODE_END(xen_entry_SYSCALL_compat)

 /* 32-bit compat sysenter target */
-SYM_CODE_START(xen_sysenter_target)
-	UNWIND_HINT_EMPTY
+SYM_CODE_START(xen_entry_SYSENTER_compat)
+	UNWIND_HINT_ENTRY
 	ENDBR
 	/*
 	 * NB: Xen is polite and clears TF from EFLAGS for us.  This means
@ -291,19 +291,19 @@ SYM_CODE_START(xen_sysenter_target)
 	movq $__USER32_CS, 1*8(%rsp)

 	jmp entry_SYSENTER_compat_after_hwframe
-SYM_CODE_END(xen_sysenter_target)
+SYM_CODE_END(xen_entry_SYSENTER_compat)

 #else /* !CONFIG_IA32_EMULATION */

-SYM_CODE_START(xen_syscall32_target)
-SYM_CODE_START(xen_sysenter_target)
-	UNWIND_HINT_EMPTY
+SYM_CODE_START(xen_entry_SYSCALL_compat)
+SYM_CODE_START(xen_entry_SYSENTER_compat)
+	UNWIND_HINT_ENTRY
 	ENDBR
 	lea 16(%rsp), %rsp	/* strip %rcx, %r11 */
 	mov $-ENOSYS, %rax
 	pushq $0
 	jmp hypercall_iret
-SYM_CODE_END(xen_sysenter_target)
-SYM_CODE_END(xen_syscall32_target)
+SYM_CODE_END(xen_entry_SYSENTER_compat)
+SYM_CODE_END(xen_entry_SYSCALL_compat)

 #endif	/* CONFIG_IA32_EMULATION */
--- a/arch/x86/xen/xen-head.S
+++ b/arch/x86/xen/xen-head.S
@ -26,6 +26,7 @@ SYM_CODE_START(hypercall_page)
 	.rept (PAGE_SIZE / 32)
 		UNWIND_HINT_FUNC
 		ANNOTATE_NOENDBR
+		ANNOTATE_UNRET_SAFE
 		ret
 		/*
 		 * Xen will write the hypercall page, and sort out ENDBR.
--- a/arch/x86/xen/xen-ops.h
+++ b/arch/x86/xen/xen-ops.h
@ -10,10 +10,10 @@
 /* These are code, but not functions.  Defined in entry.S */
 extern const char xen_failsafe_callback[];

-void xen_sysenter_target(void);
+void xen_entry_SYSENTER_compat(void);
 #ifdef CONFIG_X86_64
-void xen_syscall_target(void);
-void xen_syscall32_target(void);
+void xen_entry_SYSCALL_64(void);
+void xen_entry_SYSCALL_compat(void);
 #endif

 extern void *xen_initial_gdt;
--- a/drivers/base/cpu.c
+++ b/drivers/base/cpu.c
@ -570,6 +570,12 @@ ssize_t __weak cpu_show_mmio_stale_data(struct device *dev,
 	return sysfs_emit(buf, "Not affected\n");
 }

+ssize_t __weak cpu_show_retbleed(struct device *dev,
+				 struct device_attribute *attr, char *buf)
+{
+	return sysfs_emit(buf, "Not affected\n");
+}
+
 static DEVICE_ATTR(meltdown, 0444, cpu_show_meltdown, NULL);
 static DEVICE_ATTR(spectre_v1, 0444, cpu_show_spectre_v1, NULL);
 static DEVICE_ATTR(spectre_v2, 0444, cpu_show_spectre_v2, NULL);
@ -580,6 +586,7 @@ static DEVICE_ATTR(tsx_async_abort, 0444, cpu_show_tsx_async_abort, NULL);
 static DEVICE_ATTR(itlb_multihit, 0444, cpu_show_itlb_multihit, NULL);
 static DEVICE_ATTR(srbds, 0444, cpu_show_srbds, NULL);
 static DEVICE_ATTR(mmio_stale_data, 0444, cpu_show_mmio_stale_data, NULL);
+static DEVICE_ATTR(retbleed, 0444, cpu_show_retbleed, NULL);

 static struct attribute *cpu_root_vulnerabilities_attrs[] = {
 	&dev_attr_meltdown.attr,
@ -592,6 +599,7 @@ static struct attribute *cpu_root_vulnerabilities_attrs[] = {
 	&dev_attr_itlb_multihit.attr,
 	&dev_attr_srbds.attr,
 	&dev_attr_mmio_stale_data.attr,
+	&dev_attr_retbleed.attr,
 	NULL
 };

--- a/drivers/idle/intel_idle.c
+++ b/drivers/idle/intel_idle.c
@ -47,11 +47,13 @@
 #include <linux/tick.h>
 #include <trace/events/power.h>
 #include <linux/sched.h>
+#include <linux/sched/smt.h>
 #include <linux/notifier.h>
 #include <linux/cpu.h>
 #include <linux/moduleparam.h>
 #include <asm/cpu_device_id.h>
 #include <asm/intel-family.h>
+#include <asm/nospec-branch.h>
 #include <asm/mwait.h>
 #include <asm/msr.h>

@ -105,6 +107,12 @@ static unsigned int mwait_substates __initdata;
 */
 #define CPUIDLE_FLAG_ALWAYS_ENABLE	BIT(15)

+/*
+ * Disable IBRS across idle (when KERNEL_IBRS), is exclusive vs IRQ_ENABLE
+ * above.
+ */
+#define CPUIDLE_FLAG_IBRS		BIT(16)
+
 /*
 * MWAIT takes an 8-bit "hint" in EAX "suggesting"
 * the C-state (top nibble) and sub-state (bottom nibble)
@ -159,6 +167,24 @@ static __cpuidle int intel_idle_irq(struct cpuidle_device *dev,
 	return ret;
 }

+static __cpuidle int intel_idle_ibrs(struct cpuidle_device *dev,
+				     struct cpuidle_driver *drv, int index)
+{
+	bool smt_active = sched_smt_active();
+	u64 spec_ctrl = spec_ctrl_current();
+	int ret;
+
+	if (smt_active)
+		wrmsrl(MSR_IA32_SPEC_CTRL, 0);
+
+	ret = __intel_idle(dev, drv, index);
+
+	if (smt_active)
+		wrmsrl(MSR_IA32_SPEC_CTRL, spec_ctrl);
+
+	return ret;
+}
+
 /**
 * intel_idle_s2idle - Ask the processor to enter the given idle state.
 * @dev: cpuidle device of the target CPU.
@ -680,7 +706,7 @@ static struct cpuidle_state skl_cstates[] __initdata = {
 	{
 		.name = "C6",
 		.desc = "MWAIT 0x20",
-		.flags = MWAIT2flg(0x20) | CPUIDLE_FLAG_TLB_FLUSHED,
+		.flags = MWAIT2flg(0x20) | CPUIDLE_FLAG_TLB_FLUSHED | CPUIDLE_FLAG_IBRS,
 		.exit_latency = 85,
 		.target_residency = 200,
 		.enter = &intel_idle,
@ -688,7 +714,7 @@ static struct cpuidle_state skl_cstates[] __initdata = {
 	{
 		.name = "C7s",
 		.desc = "MWAIT 0x33",
-		.flags = MWAIT2flg(0x33) | CPUIDLE_FLAG_TLB_FLUSHED,
+		.flags = MWAIT2flg(0x33) | CPUIDLE_FLAG_TLB_FLUSHED | CPUIDLE_FLAG_IBRS,
 		.exit_latency = 124,
 		.target_residency = 800,
 		.enter = &intel_idle,
@ -696,7 +722,7 @@ static struct cpuidle_state skl_cstates[] __initdata = {
 	{
 		.name = "C8",
 		.desc = "MWAIT 0x40",
-		.flags = MWAIT2flg(0x40) | CPUIDLE_FLAG_TLB_FLUSHED,
+		.flags = MWAIT2flg(0x40) | CPUIDLE_FLAG_TLB_FLUSHED | CPUIDLE_FLAG_IBRS,
 		.exit_latency = 200,
 		.target_residency = 800,
 		.enter = &intel_idle,
@ -704,7 +730,7 @@ static struct cpuidle_state skl_cstates[] __initdata = {
 	{
 		.name = "C9",
 		.desc = "MWAIT 0x50",
-		.flags = MWAIT2flg(0x50) | CPUIDLE_FLAG_TLB_FLUSHED,
+		.flags = MWAIT2flg(0x50) | CPUIDLE_FLAG_TLB_FLUSHED | CPUIDLE_FLAG_IBRS,
 		.exit_latency = 480,
 		.target_residency = 5000,
 		.enter = &intel_idle,
@ -712,7 +738,7 @@ static struct cpuidle_state skl_cstates[] __initdata = {
 	{
 		.name = "C10",
 		.desc = "MWAIT 0x60",
-		.flags = MWAIT2flg(0x60) | CPUIDLE_FLAG_TLB_FLUSHED,
+		.flags = MWAIT2flg(0x60) | CPUIDLE_FLAG_TLB_FLUSHED | CPUIDLE_FLAG_IBRS,
 		.exit_latency = 890,
 		.target_residency = 5000,
 		.enter = &intel_idle,
@ -741,7 +767,7 @@ static struct cpuidle_state skx_cstates[] __initdata = {
 	{
 		.name = "C6",
 		.desc = "MWAIT 0x20",
-		.flags = MWAIT2flg(0x20) | CPUIDLE_FLAG_TLB_FLUSHED,
+		.flags = MWAIT2flg(0x20) | CPUIDLE_FLAG_TLB_FLUSHED | CPUIDLE_FLAG_IBRS,
 		.exit_latency = 133,
 		.target_residency = 600,
 		.enter = &intel_idle,
@ -1819,6 +1845,12 @@ static void __init intel_idle_init_cstates_icpu(struct cpuidle_driver *drv)
 		if (cpuidle_state_table[cstate].flags & CPUIDLE_FLAG_IRQ_ENABLE)
 			drv->states[drv->state_count].enter = intel_idle_irq;

+		if (cpu_feature_enabled(X86_FEATURE_KERNEL_IBRS) &&
+		    cpuidle_state_table[cstate].flags & CPUIDLE_FLAG_IBRS) {
+			WARN_ON_ONCE(cpuidle_state_table[cstate].flags & CPUIDLE_FLAG_IRQ_ENABLE);
+			drv->states[drv->state_count].enter = intel_idle_ibrs;
+		}
+
 		if ((disabled_states_mask & BIT(drv->state_count)) ||
 		    ((icpu->use_acpi || force_use_acpi) &&
 		     intel_idle_off_by_default(mwait_hint) &&
--- a/include/linux/cpu.h
+++ b/include/linux/cpu.h
@ -68,6 +68,8 @@ extern ssize_t cpu_show_srbds(struct device *dev, struct device_attribute *attr,
 extern ssize_t cpu_show_mmio_stale_data(struct device *dev,
 					struct device_attribute *attr,
 					char *buf);
+extern ssize_t cpu_show_retbleed(struct device *dev,
+				 struct device_attribute *attr, char *buf);

 extern __printf(4, 5)
 struct device *cpu_device_create(struct device *parent, void *drvdata,
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@ -1513,7 +1513,7 @@ static inline void kvm_arch_end_assignment(struct kvm *kvm)
 {
 }

-static inline bool kvm_arch_has_assigned_device(struct kvm *kvm)
+static __always_inline bool kvm_arch_has_assigned_device(struct kvm *kvm)
 {
 	return false;
 }
--- a/include/linux/objtool.h
+++ b/include/linux/objtool.h
@ -32,11 +32,16 @@ struct unwind_hint {
 *
 * UNWIND_HINT_FUNC: Generate the unwind metadata of a callable function.
 * Useful for code which doesn't have an ELF function annotation.
+ *
+ * UNWIND_HINT_ENTRY: machine entry without stack, SYSCALL/SYSENTER etc.
 */
 #define UNWIND_HINT_TYPE_CALL		0
 #define UNWIND_HINT_TYPE_REGS		1
 #define UNWIND_HINT_TYPE_REGS_PARTIAL	2
 #define UNWIND_HINT_TYPE_FUNC		3
+#define UNWIND_HINT_TYPE_ENTRY		4
+#define UNWIND_HINT_TYPE_SAVE		5
+#define UNWIND_HINT_TYPE_RESTORE	6

 #ifdef CONFIG_OBJTOOL

@ -124,7 +129,7 @@ struct unwind_hint {
 * the debuginfo as necessary.  It will also warn if it sees any
 * inconsistencies.
 */
-.macro UNWIND_HINT sp_reg:req sp_offset=0 type:req end=0
+.macro UNWIND_HINT type:req sp_reg=0 sp_offset=0 end=0
 .Lunwind_hint_ip_\@:
 	.pushsection .discard.unwind_hints
 		/* struct unwind_hint */
@ -177,7 +182,7 @@ struct unwind_hint {
 #define ASM_REACHABLE
 #else
 #define ANNOTATE_INTRA_FUNCTION_CALL
-.macro UNWIND_HINT sp_reg:req sp_offset=0 type:req end=0
+.macro UNWIND_HINT type:req sp_reg=0 sp_offset=0 end=0
 .endm
 .macro STACK_FRAME_NON_STANDARD func:req
 .endm
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@ -236,6 +236,7 @@ objtool_args =								\
 	$(if $(CONFIG_FTRACE_MCOUNT_USE_OBJTOOL), --mcount)		\
 	$(if $(CONFIG_UNWINDER_ORC), --orc)				\
 	$(if $(CONFIG_RETPOLINE), --retpoline)				\
+	$(if $(CONFIG_RETHUNK), --rethunk)				\
 	$(if $(CONFIG_SLS), --sls)					\
 	$(if $(CONFIG_STACK_VALIDATION), --stackval)			\
 	$(if $(CONFIG_HAVE_STATIC_CALL_INLINE), --static-call)		\
--- a/scripts/Makefile.vmlinux_o
+++ b/scripts/Makefile.vmlinux_o
@ -44,7 +44,7 @@ objtool-enabled := $(or $(delay-objtool),$(CONFIG_NOINSTR_VALIDATION))

 objtool_args := \
 	$(if $(delay-objtool),$(objtool_args)) \
-	$(if $(CONFIG_NOINSTR_VALIDATION), --noinstr) \
+	$(if $(CONFIG_NOINSTR_VALIDATION), --noinstr $(if $(CONFIG_CPU_UNRET_ENTRY), --unret)) \
 	$(if $(CONFIG_GCOV_KERNEL), --no-unreachable) \
 	--link

--- a/security/Kconfig
+++ b/security/Kconfig
@ -54,17 +54,6 @@ config SECURITY_NETWORK
 	  implement socket and networking access controls.
 	  If you are unsure how to answer this question, answer N.

-config PAGE_TABLE_ISOLATION
-	bool "Remove the kernel mapping in user mode"
-	default y
-	depends on (X86_64 || X86_PAE) && !UML
-	help
-	  This feature reduces the number of hardware side channels by
-	  ensuring that the majority of kernel addresses are not mapped
-	  into userspace.
-
-	  See Documentation/x86/pti.rst for more details.
-
 config SECURITY_INFINIBAND
 	bool "Infiniband Security Hooks"
 	depends on SECURITY && INFINIBAND
--- a/tools/arch/x86/include/asm/msr-index.h
+++ b/tools/arch/x86/include/asm/msr-index.h
@ -51,6 +51,8 @@
 #define SPEC_CTRL_STIBP			BIT(SPEC_CTRL_STIBP_SHIFT)	/* STIBP mask */
 #define SPEC_CTRL_SSBD_SHIFT		2	   /* Speculative Store Bypass Disable bit */
 #define SPEC_CTRL_SSBD			BIT(SPEC_CTRL_SSBD_SHIFT)	/* Speculative Store Bypass Disable */
+#define SPEC_CTRL_RRSBA_DIS_S_SHIFT	6	   /* Disable RRSBA behavior */
+#define SPEC_CTRL_RRSBA_DIS_S		BIT(SPEC_CTRL_RRSBA_DIS_S_SHIFT)

 #define MSR_IA32_PRED_CMD		0x00000049 /* Prediction Command */
 #define PRED_CMD_IBPB			BIT(0)	   /* Indirect Branch Prediction Barrier */
@ -140,6 +142,13 @@
 						 * bit available to control VERW
 						 * behavior.
 						 */
+#define ARCH_CAP_RRSBA			BIT(19)	/*
+						 * Indicates RET may use predictors
+						 * other than the RSB. With eIBRS
+						 * enabled predictions in kernel mode
+						 * are restricted to targets in
+						 * kernel.
+						 */

 #define MSR_IA32_FLUSH_CMD		0x0000010b
 #define L1D_FLUSH			BIT(0)	/*
--- a/tools/include/linux/objtool.h
+++ b/tools/include/linux/objtool.h
@ -32,11 +32,16 @@ struct unwind_hint {
 *
 * UNWIND_HINT_FUNC: Generate the unwind metadata of a callable function.
 * Useful for code which doesn't have an ELF function annotation.
+ *
+ * UNWIND_HINT_ENTRY: machine entry without stack, SYSCALL/SYSENTER etc.
 */
 #define UNWIND_HINT_TYPE_CALL		0
 #define UNWIND_HINT_TYPE_REGS		1
 #define UNWIND_HINT_TYPE_REGS_PARTIAL	2
 #define UNWIND_HINT_TYPE_FUNC		3
+#define UNWIND_HINT_TYPE_ENTRY		4
+#define UNWIND_HINT_TYPE_SAVE		5
+#define UNWIND_HINT_TYPE_RESTORE	6

 #ifdef CONFIG_OBJTOOL

@ -124,7 +129,7 @@ struct unwind_hint {
 * the debuginfo as necessary.  It will also warn if it sees any
 * inconsistencies.
 */
-.macro UNWIND_HINT sp_reg:req sp_offset=0 type:req end=0
+.macro UNWIND_HINT type:req sp_reg=0 sp_offset=0 end=0
 .Lunwind_hint_ip_\@:
 	.pushsection .discard.unwind_hints
 		/* struct unwind_hint */
@ -177,7 +182,7 @@ struct unwind_hint {
 #define ASM_REACHABLE
 #else
 #define ANNOTATE_INTRA_FUNCTION_CALL
-.macro UNWIND_HINT sp_reg:req sp_offset=0 type:req end=0
+.macro UNWIND_HINT type:req sp_reg=0 sp_offset=0 end=0
 .endm
 .macro STACK_FRAME_NON_STANDARD func:req
 .endm
--- a/tools/objtool/arch/x86/decode.c
+++ b/tools/objtool/arch/x86/decode.c
@ -787,3 +787,8 @@ bool arch_is_retpoline(struct symbol *sym)
 {
 	return !strncmp(sym->name, "__x86_indirect_", 15);
 }
+
+bool arch_is_rethunk(struct symbol *sym)
+{
+	return !strcmp(sym->name, "__x86_return_thunk");
+}
--- a/tools/objtool/builtin-check.c
+++ b/tools/objtool/builtin-check.c
@ -68,6 +68,8 @@ const struct option check_options[] = {
 	OPT_BOOLEAN('n', "noinstr", &opts.noinstr, "validate noinstr rules"),
 	OPT_BOOLEAN('o', "orc", &opts.orc, "generate ORC metadata"),
 	OPT_BOOLEAN('r', "retpoline", &opts.retpoline, "validate and annotate retpoline usage"),
+	OPT_BOOLEAN(0,   "rethunk", &opts.rethunk, "validate and annotate rethunk usage"),
+	OPT_BOOLEAN(0,   "unret", &opts.unret, "validate entry unret placement"),
 	OPT_BOOLEAN('l', "sls", &opts.sls, "validate straight-line-speculation mitigations"),
 	OPT_BOOLEAN('s', "stackval", &opts.stackval, "validate frame pointer rules"),
 	OPT_BOOLEAN('t', "static-call", &opts.static_call, "annotate static calls"),
@ -123,6 +125,7 @@ static bool opts_valid(void)
 	    opts.noinstr		||
 	    opts.orc			||
 	    opts.retpoline		||
+	    opts.rethunk		||
 	    opts.sls			||
 	    opts.stackval		||
 	    opts.static_call		||
@ -135,6 +138,11 @@ static bool opts_valid(void)
 		return true;
 	}

+	if (opts.unret && !opts.rethunk) {
+		ERROR("--unret requires --rethunk");
+		return false;
+	}
+
 	if (opts.dump_orc)
 		return true;

@ -163,6 +171,11 @@ static bool link_opts_valid(struct objtool_file *file)
 		return false;
 	}

+	if (opts.unret) {
+		ERROR("--unret requires --link");
+		return false;
+	}
+
 	return true;
 }

--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@ -376,7 +376,8 @@ static int decode_instructions(struct objtool_file *file)
 			sec->text = true;

 		if (!strcmp(sec->name, ".noinstr.text") ||
-		    !strcmp(sec->name, ".entry.text"))
+		    !strcmp(sec->name, ".entry.text") ||
+		    !strncmp(sec->name, ".text.__x86.", 12))
 			sec->noinstr = true;

 		for (offset = 0; offset < sec->sh.sh_size; offset += insn->len) {
@ -749,6 +750,52 @@ static int create_retpoline_sites_sections(struct objtool_file *file)
 	return 0;
 }

+static int create_return_sites_sections(struct objtool_file *file)
+{
+	struct instruction *insn;
+	struct section *sec;
+	int idx;
+
+	sec = find_section_by_name(file->elf, ".return_sites");
+	if (sec) {
+		WARN("file already has .return_sites, skipping");
+		return 0;
+	}
+
+	idx = 0;
+	list_for_each_entry(insn, &file->return_thunk_list, call_node)
+		idx++;
+
+	if (!idx)
+		return 0;
+
+	sec = elf_create_section(file->elf, ".return_sites", 0,
+				 sizeof(int), idx);
+	if (!sec) {
+		WARN("elf_create_section: .return_sites");
+		return -1;
+	}
+
+	idx = 0;
+	list_for_each_entry(insn, &file->return_thunk_list, call_node) {
+
+		int *site = (int *)sec->data->d_buf + idx;
+		*site = 0;
+
+		if (elf_add_reloc_to_insn(file->elf, sec,
+					  idx * sizeof(int),
+					  R_X86_64_PC32,
+					  insn->sec, insn->offset)) {
+			WARN("elf_add_reloc_to_insn: .return_sites");
+			return -1;
+		}
+
+		idx++;
+	}
+
+	return 0;
+}
+
 static int create_ibt_endbr_seal_sections(struct objtool_file *file)
 {
 	struct instruction *insn;
@ -1083,6 +1130,11 @@ __weak bool arch_is_retpoline(struct symbol *sym)
 	return false;
 }

+__weak bool arch_is_rethunk(struct symbol *sym)
+{
+	return false;
+}
+
 #define NEGATIVE_RELOC	((void *)-1L)

 static struct reloc *insn_reloc(struct objtool_file *file, struct instruction *insn)
@ -1250,6 +1302,19 @@ static void add_retpoline_call(struct objtool_file *file, struct instruction *in
 	annotate_call_site(file, insn, false);
 }

+static void add_return_call(struct objtool_file *file, struct instruction *insn, bool add)
+{
+	/*
+	 * Return thunk tail calls are really just returns in disguise,
+	 * so convert them accordingly.
+	 */
+	insn->type = INSN_RETURN;
+	insn->retpoline_safe = true;
+
+	if (add)
+		list_add_tail(&insn->call_node, &file->return_thunk_list);
+}
+
 static bool same_function(struct instruction *insn1, struct instruction *insn2)
 {
 	return insn1->func->pfunc == insn2->func->pfunc;
@ -1302,6 +1367,9 @@ static int add_jump_destinations(struct objtool_file *file)
 		} else if (reloc->sym->retpoline_thunk) {
 			add_retpoline_call(file, insn);
 			continue;
+		} else if (reloc->sym->return_thunk) {
+			add_return_call(file, insn, true);
+			continue;
 		} else if (insn->func) {
 			/*
 			 * External sibling call or internal sibling call with
@ -1320,6 +1388,21 @@ static int add_jump_destinations(struct objtool_file *file)

 		jump_dest = find_insn(file, dest_sec, dest_off);
 		if (!jump_dest) {
+			struct symbol *sym = find_symbol_by_offset(dest_sec, dest_off);
+
+			/*
+			 * This is a special case for zen_untrain_ret().
+			 * It jumps to __x86_return_thunk(), but objtool
+			 * can't find the thunk's starting RET
+			 * instruction, because the RET is also in the
+			 * middle of another instruction.  Objtool only
+			 * knows about the outer instruction.
+			 */
+			if (sym && sym->return_thunk) {
+				add_return_call(file, insn, false);
+				continue;
+			}
+
 			WARN_FUNC("can't find jump dest instruction at %s+0x%lx",
 				  insn->sec, insn->offset, dest_sec->name,
 				  dest_off);
@ -1949,16 +2032,35 @@ static int read_unwind_hints(struct objtool_file *file)

 		insn->hint = true;

-		if (opts.ibt && hint->type == UNWIND_HINT_TYPE_REGS_PARTIAL) {
+		if (hint->type == UNWIND_HINT_TYPE_SAVE) {
+			insn->hint = false;
+			insn->save = true;
+			continue;
+		}
+
+		if (hint->type == UNWIND_HINT_TYPE_RESTORE) {
+			insn->restore = true;
+			continue;
+		}
+
+		if (hint->type == UNWIND_HINT_TYPE_REGS_PARTIAL) {
 			struct symbol *sym = find_symbol_by_offset(insn->sec, insn->offset);

-			if (sym && sym->bind == STB_GLOBAL &&
-			    insn->type != INSN_ENDBR && !insn->noendbr) {
-				WARN_FUNC("UNWIND_HINT_IRET_REGS without ENDBR",
-					  insn->sec, insn->offset);
+			if (sym && sym->bind == STB_GLOBAL) {
+				if (opts.ibt && insn->type != INSN_ENDBR && !insn->noendbr) {
+					WARN_FUNC("UNWIND_HINT_IRET_REGS without ENDBR",
+						  insn->sec, insn->offset);
+				}
+
+				insn->entry = 1;
 			}
 		}

+		if (hint->type == UNWIND_HINT_TYPE_ENTRY) {
+			hint->type = UNWIND_HINT_TYPE_CALL;
+			insn->entry = 1;
+		}
+
 		if (hint->type == UNWIND_HINT_TYPE_FUNC) {
 			insn->cfi = &func_cfi;
 			continue;
@ -2032,8 +2134,10 @@ static int read_retpoline_hints(struct objtool_file *file)
 		}

 		if (insn->type != INSN_JUMP_DYNAMIC &&
-		    insn->type != INSN_CALL_DYNAMIC) {
-			WARN_FUNC("retpoline_safe hint not an indirect jump/call",
+		    insn->type != INSN_CALL_DYNAMIC &&
+		    insn->type != INSN_RETURN &&
+		    insn->type != INSN_NOP) {
+			WARN_FUNC("retpoline_safe hint not an indirect jump/call/ret/nop",
 				  insn->sec, insn->offset);
 			return -1;
 		}
@ -2184,6 +2288,9 @@ static int classify_symbols(struct objtool_file *file)
 			if (arch_is_retpoline(func))
 				func->retpoline_thunk = true;

+			if (arch_is_rethunk(func))
+				func->return_thunk = true;
+
 			if (!strcmp(func->name, "__fentry__"))
 				func->fentry = true;

@ -3218,8 +3325,8 @@ static int validate_branch(struct objtool_file *file, struct symbol *func,
 			return 1;
 		}

-		visited = 1 << state.uaccess;
-		if (insn->visited) {
+		visited = VISITED_BRANCH << state.uaccess;
+		if (insn->visited & VISITED_BRANCH_MASK) {
 			if (!insn->hint && !insn_cfi_match(insn, &state.cfi))
 				return 1;

@ -3233,6 +3340,35 @@ static int validate_branch(struct objtool_file *file, struct symbol *func,
 			state.instr += insn->instr;

 		if (insn->hint) {
+			if (insn->restore) {
+				struct instruction *save_insn, *i;
+
+				i = insn;
+				save_insn = NULL;
+
+				sym_for_each_insn_continue_reverse(file, func, i) {
+					if (i->save) {
+						save_insn = i;
+						break;
+					}
+				}
+
+				if (!save_insn) {
+					WARN_FUNC("no corresponding CFI save for CFI restore",
+						  sec, insn->offset);
+					return 1;
+				}
+
+				if (!save_insn->visited) {
+					WARN_FUNC("objtool isn't smart enough to handle this CFI save/restore combo",
+						  sec, insn->offset);
+					return 1;
+				}
+
+				insn->cfi = save_insn->cfi;
+				nr_cfi_reused++;
+			}
+
 			state.cfi = *insn->cfi;
 		} else {
 			/* XXX track if we actually changed state.cfi */
@ -3433,6 +3569,145 @@ static int validate_unwind_hints(struct objtool_file *file, struct section *sec)
 	return warnings;
 }

+/*
+ * Validate rethunk entry constraint: must untrain RET before the first RET.
+ *
+ * Follow every branch (intra-function) and ensure ANNOTATE_UNRET_END comes
+ * before an actual RET instruction.
+ */
+static int validate_entry(struct objtool_file *file, struct instruction *insn)
+{
+	struct instruction *next, *dest;
+	int ret, warnings = 0;
+
+	for (;;) {
+		next = next_insn_to_validate(file, insn);
+
+		if (insn->visited & VISITED_ENTRY)
+			return 0;
+
+		insn->visited |= VISITED_ENTRY;
+
+		if (!insn->ignore_alts && !list_empty(&insn->alts)) {
+			struct alternative *alt;
+			bool skip_orig = false;
+
+			list_for_each_entry(alt, &insn->alts, list) {
+				if (alt->skip_orig)
+					skip_orig = true;
+
+				ret = validate_entry(file, alt->insn);
+				if (ret) {
+				        if (opts.backtrace)
+						BT_FUNC("(alt)", insn);
+					return ret;
+				}
+			}
+
+			if (skip_orig)
+				return 0;
+		}
+
+		switch (insn->type) {
+
+		case INSN_CALL_DYNAMIC:
+		case INSN_JUMP_DYNAMIC:
+		case INSN_JUMP_DYNAMIC_CONDITIONAL:
+			WARN_FUNC("early indirect call", insn->sec, insn->offset);
+			return 1;
+
+		case INSN_JUMP_UNCONDITIONAL:
+		case INSN_JUMP_CONDITIONAL:
+			if (!is_sibling_call(insn)) {
+				if (!insn->jump_dest) {
+					WARN_FUNC("unresolved jump target after linking?!?",
+						  insn->sec, insn->offset);
+					return -1;
+				}
+				ret = validate_entry(file, insn->jump_dest);
+				if (ret) {
+					if (opts.backtrace) {
+						BT_FUNC("(branch%s)", insn,
+							insn->type == INSN_JUMP_CONDITIONAL ? "-cond" : "");
+					}
+					return ret;
+				}
+
+				if (insn->type == INSN_JUMP_UNCONDITIONAL)
+					return 0;
+
+				break;
+			}
+
+			/* fallthrough */
+		case INSN_CALL:
+			dest = find_insn(file, insn->call_dest->sec,
+					 insn->call_dest->offset);
+			if (!dest) {
+				WARN("Unresolved function after linking!?: %s",
+				     insn->call_dest->name);
+				return -1;
+			}
+
+			ret = validate_entry(file, dest);
+			if (ret) {
+				if (opts.backtrace)
+					BT_FUNC("(call)", insn);
+				return ret;
+			}
+			/*
+			 * If a call returns without error, it must have seen UNTRAIN_RET.
+			 * Therefore any non-error return is a success.
+			 */
+			return 0;
+
+		case INSN_RETURN:
+			WARN_FUNC("RET before UNTRAIN", insn->sec, insn->offset);
+			return 1;
+
+		case INSN_NOP:
+			if (insn->retpoline_safe)
+				return 0;
+			break;
+
+		default:
+			break;
+		}
+
+		if (!next) {
+			WARN_FUNC("teh end!", insn->sec, insn->offset);
+			return -1;
+		}
+		insn = next;
+	}
+
+	return warnings;
+}
+
+/*
+ * Validate that all branches starting at 'insn->entry' encounter UNRET_END
+ * before RET.
+ */
+static int validate_unret(struct objtool_file *file)
+{
+	struct instruction *insn;
+	int ret, warnings = 0;
+
+	for_each_insn(file, insn) {
+		if (!insn->entry)
+			continue;
+
+		ret = validate_entry(file, insn);
+		if (ret < 0) {
+			WARN_FUNC("Failed UNRET validation", insn->sec, insn->offset);
+			return ret;
+		}
+		warnings += ret;
+	}
+
+	return warnings;
+}
+
 static int validate_retpoline(struct objtool_file *file)
 {
 	struct instruction *insn;
@ -3440,7 +3715,8 @@ static int validate_retpoline(struct objtool_file *file)

 	for_each_insn(file, insn) {
 		if (insn->type != INSN_JUMP_DYNAMIC &&
-		    insn->type != INSN_CALL_DYNAMIC)
+		    insn->type != INSN_CALL_DYNAMIC &&
+		    insn->type != INSN_RETURN)
 			continue;

 		if (insn->retpoline_safe)
@ -3455,9 +3731,17 @@ static int validate_retpoline(struct objtool_file *file)
 		if (!strcmp(insn->sec->name, ".init.text") && !opts.module)
 			continue;

-		WARN_FUNC("indirect %s found in RETPOLINE build",
-			  insn->sec, insn->offset,
-			  insn->type == INSN_JUMP_DYNAMIC ? "jump" : "call");
+		if (insn->type == INSN_RETURN) {
+			if (opts.rethunk) {
+				WARN_FUNC("'naked' return found in RETHUNK build",
+					  insn->sec, insn->offset);
+			} else
+				continue;
+		} else {
+			WARN_FUNC("indirect %s found in RETPOLINE build",
+				  insn->sec, insn->offset,
+				  insn->type == INSN_JUMP_DYNAMIC ? "jump" : "call");
+		}

 		warnings++;
 	}
@ -3945,6 +4229,17 @@ int check(struct objtool_file *file)
 		warnings += ret;
 	}

+	if (opts.unret) {
+		/*
+		 * Must be after validate_branch() and friends, it plays
+		 * further games with insn->visited.
+		 */
+		ret = validate_unret(file);
+		if (ret < 0)
+			return ret;
+		warnings += ret;
+	}
+
 	if (opts.ibt) {
 		ret = validate_ibt(file);
 		if (ret < 0)
@ -3973,6 +4268,13 @@ int check(struct objtool_file *file)
 		warnings += ret;
 	}

+	if (opts.rethunk) {
+		ret = create_return_sites_sections(file);
+		if (ret < 0)
+			goto out;
+		warnings += ret;
+	}
+
 	if (opts.mcount) {
 		ret = create_mcount_loc_sections(file);
 		if (ret < 0)
--- a/tools/objtool/include/objtool/arch.h
+++ b/tools/objtool/include/objtool/arch.h
@ -89,6 +89,7 @@ const char *arch_ret_insn(int len);
 int arch_decode_hint_reg(u8 sp_reg, int *base);

 bool arch_is_retpoline(struct symbol *sym);
+bool arch_is_rethunk(struct symbol *sym);

 int arch_rewrite_retpolines(struct objtool_file *file);

--- a/tools/objtool/include/objtool/builtin.h
+++ b/tools/objtool/include/objtool/builtin.h
@ -19,6 +19,8 @@ struct opts {
 	bool noinstr;
 	bool orc;
 	bool retpoline;
+	bool rethunk;
+	bool unret;
 	bool sls;
 	bool stackval;
 	bool static_call;
--- a/tools/objtool/include/objtool/check.h
+++ b/tools/objtool/include/objtool/check.h
@ -46,16 +46,19 @@ struct instruction {
 	enum insn_type type;
 	unsigned long immediate;

-	u8 dead_end	: 1,
-	   ignore	: 1,
-	   ignore_alts	: 1,
-	   hint		: 1,
-	   retpoline_safe : 1,
-	   noendbr	: 1;
-		/* 2 bit hole */
+	u16 dead_end		: 1,
+	   ignore		: 1,
+	   ignore_alts		: 1,
+	   hint			: 1,
+	   save			: 1,
+	   restore		: 1,
+	   retpoline_safe	: 1,
+	   noendbr		: 1,
+	   entry		: 1;
+		/* 7 bit hole */
+
 	s8 instr;
 	u8 visited;
-	/* u8 hole */

 	struct alt_group *alt_group;
 	struct symbol *call_dest;
@ -69,6 +72,11 @@ struct instruction {
 	struct cfi_state *cfi;
 };

+#define VISITED_BRANCH		0x01
+#define VISITED_BRANCH_UACCESS	0x02
+#define VISITED_BRANCH_MASK	0x03
+#define VISITED_ENTRY		0x04
+
 static inline bool is_static_jump(struct instruction *insn)
 {
 	return insn->type == INSN_JUMP_CONDITIONAL ||
--- a/tools/objtool/include/objtool/elf.h
+++ b/tools/objtool/include/objtool/elf.h
@ -57,6 +57,7 @@ struct symbol {
 	u8 uaccess_safe      : 1;
 	u8 static_call_tramp : 1;
 	u8 retpoline_thunk   : 1;
+	u8 return_thunk      : 1;
 	u8 fentry            : 1;
 	u8 profiling_func    : 1;
 	struct list_head pv_target;
--- a/tools/objtool/include/objtool/objtool.h
+++ b/tools/objtool/include/objtool/objtool.h
@ -24,6 +24,7 @@ struct objtool_file {
 	struct list_head insn_list;
 	DECLARE_HASHTABLE(insn_hash, 20);
 	struct list_head retpoline_call_list;
+	struct list_head return_thunk_list;
 	struct list_head static_call_list;
 	struct list_head mcount_loc_list;
 	struct list_head endbr_list;
--- a/tools/objtool/objtool.c
+++ b/tools/objtool/objtool.c
@ -102,6 +102,7 @@ struct objtool_file *objtool_open_read(const char *_objname)
 	INIT_LIST_HEAD(&file.insn_list);
 	hash_init(file.insn_hash);
 	INIT_LIST_HEAD(&file.retpoline_call_list);
+	INIT_LIST_HEAD(&file.return_thunk_list);
 	INIT_LIST_HEAD(&file.static_call_list);
 	INIT_LIST_HEAD(&file.mcount_loc_list);
 	INIT_LIST_HEAD(&file.endbr_list);