kernel hardening fixes for v6.2-rc1

- Fix CFI failure with KASAN (Sami Tolvanen)
 
 - Fix LKDTM + CFI under GCC 7 and 8 (Kristina Martsenko)
 
 - Limit CONFIG_ZERO_CALL_USED_REGS to Clang > 15.0.6 (Nathan Chancellor)
 
 - Ignore "contents" argument in LoadPin's LSM hook handling
 
 - Fix paste-o in /sys/kernel/warn_count API docs
 
 - Use READ_ONCE() consistently for oops/warn limit reading
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Merge tag 'hardening-v6.2-rc1-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux

Pull kernel hardening fixes from Kees Cook:

 - Fix CFI failure with KASAN (Sami Tolvanen)

 - Fix LKDTM + CFI under GCC 7 and 8 (Kristina Martsenko)

 - Limit CONFIG_ZERO_CALL_USED_REGS to Clang > 15.0.6 (Nathan
   Chancellor)

 - Ignore "contents" argument in LoadPin's LSM hook handling

 - Fix paste-o in /sys/kernel/warn_count API docs

 - Use READ_ONCE() consistently for oops/warn limit reading

* tag 'hardening-v6.2-rc1-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux:
  cfi: Fix CFI failure with KASAN
  exit: Use READ_ONCE() for all oops/warn limit reads
  security: Restrict CONFIG_ZERO_CALL_USED_REGS to gcc or clang > 15.0.6
  lkdtm: cfi: Make PAC test work with GCC 7 and 8
  docs: Fix path paste-o for /sys/kernel/warn_count
  LoadPin: Ignore the "contents" argument of the LSM hooks

Documentation/ABI/testing/sysfs-kernel-warn_count

@@ -1,4 +1,4 @@
-What:		/sys/kernel/oops_count
+What:		/sys/kernel/warn_count
 Date:		November 2022
 KernelVersion:	6.2.0
 Contact:	Linux Kernel Hardening List <linux-hardening@vger.kernel.org>

drivers/misc/lkdtm/cfi.c

@@ -54,7 +54,11 @@ static void lkdtm_CFI_FORWARD_PROTO(void)
 # ifdef CONFIG_ARM64_BTI_KERNEL
 #  define __no_pac             "branch-protection=bti"
 # else
-#  define __no_pac             "branch-protection=none"
+#  ifdef CONFIG_CC_HAS_BRANCH_PROT_PAC_RET
+#   define __no_pac            "branch-protection=none"
+#  else
+#   define __no_pac            "sign-return-address=none"
+#  endif
 # endif
 # define __no_ret_protection   __noscs __attribute__((__target__(__no_pac)))
 #else

kernel/Makefile

@@ -41,9 +41,6 @@ UBSAN_SANITIZE_kcov.o := n
 KMSAN_SANITIZE_kcov.o := n
 CFLAGS_kcov.o := $(call cc-option, -fno-conserve-stack) -fno-stack-protector
 
-# Don't instrument error handlers
-CFLAGS_REMOVE_cfi.o := $(CC_FLAGS_CFI)
-
 obj-y += sched/
 obj-y += locking/
 obj-y += power/

kernel/exit.c

@@ -931,6 +931,7 @@ void __noreturn make_task_dead(int signr)
 	 * Then do everything else.
 	 */
 	struct task_struct *tsk = current;
+	unsigned int limit;
 
 	if (unlikely(in_interrupt()))
 		panic("Aiee, killing interrupt handler!");
@@ -954,8 +955,9 @@ void __noreturn make_task_dead(int signr)
 	 * To make sure this can't happen, place an upper bound on how often the
 	 * kernel may oops without panic().
 	 */
-	if (atomic_inc_return(&oops_count) >= READ_ONCE(oops_limit) && oops_limit)
-		panic("Oopsed too often (kernel.oops_limit is %d)", oops_limit);
+	limit = READ_ONCE(oops_limit);
+	if (atomic_inc_return(&oops_count) >= limit && limit)
+		panic("Oopsed too often (kernel.oops_limit is %d)", limit);
 
 	/*
 	 * We're taking recursive faults here in make_task_dead. Safest is to just

kernel/panic.c

@@ -232,12 +232,15 @@ static void panic_print_sys_info(bool console_flush)
 
 void check_panic_on_warn(const char *origin)
 {
+	unsigned int limit;
+
 	if (panic_on_warn)
 		panic("%s: panic_on_warn set ...\n", origin);
 
-	if (atomic_inc_return(&warn_count) >= READ_ONCE(warn_limit) && warn_limit)
+	limit = READ_ONCE(warn_limit);
+	if (atomic_inc_return(&warn_count) >= limit && limit)
 		panic("%s: system warned too often (kernel.warn_limit is %d)",
-		      origin, warn_limit);
+		      origin, limit);
 }
 
 /**

security/Kconfig.hardening

@@ -257,6 +257,9 @@ config INIT_ON_FREE_DEFAULT_ON
 
 config CC_HAS_ZERO_CALL_USED_REGS
 	def_bool $(cc-option,-fzero-call-used-regs=used-gpr)
+	# https://github.com/ClangBuiltLinux/linux/issues/1766
+	# https://github.com/llvm/llvm-project/issues/59242
+	depends on !CC_IS_CLANG || CLANG_VERSION > 150006
 
 config ZERO_CALL_USED_REGS
 	bool "Enable register zeroing on function exit"

security/loadpin/loadpin.c

@@ -122,21 +122,11 @@ static void loadpin_sb_free_security(struct super_block *mnt_sb)
 	}
 }
 
-static int loadpin_read_file(struct file *file, enum kernel_read_file_id id,
-			     bool contents)
+static int loadpin_check(struct file *file, enum kernel_read_file_id id)
 {
 	struct super_block *load_root;
 	const char *origin = kernel_read_file_id_str(id);
 
-	/*
-	 * If we will not know that we'll be seeing the full contents
-	 * then we cannot trust a load will be complete and unchanged
-	 * off disk. Treat all contents=false hooks as if there were
-	 * no associated file struct.
-	 */
-	if (!contents)
-		file = NULL;
-
 	/* If the file id is excluded, ignore the pinning. */
 	if ((unsigned int)id < ARRAY_SIZE(ignore_read_file_id) &&
 	    ignore_read_file_id[id]) {
@@ -192,9 +182,25 @@ static int loadpin_read_file(struct file *file, enum kernel_read_file_id id,
 	return 0;
 }
 
+static int loadpin_read_file(struct file *file, enum kernel_read_file_id id,
+			     bool contents)
+{
+	/*
+	 * LoadPin only cares about the _origin_ of a file, not its
+	 * contents, so we can ignore the "are full contents available"
+	 * argument here.
+	 */
+	return loadpin_check(file, id);
+}
+
 static int loadpin_load_data(enum kernel_load_data_id id, bool contents)
 {
-	return loadpin_read_file(NULL, (enum kernel_read_file_id) id, contents);
+	/*
+	 * LoadPin only cares about the _origin_ of a file, not its
+	 * contents, so a NULL file is passed, and we can ignore the
+	 * state of "contents".
+	 */
+	return loadpin_check(NULL, (enum kernel_read_file_id) id);
 }
 
 static struct security_hook_list loadpin_hooks[] __lsm_ro_after_init = {