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linux/arch/arm/include/asm/current.h

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ARM: smp: Store current pointer in TPIDRURO register if available Now that the user space TLS register is assigned on every return to user space, we can use it to keep the 'current' pointer while running in the kernel. This removes the need to access it via thread_info, which is located at the base of the stack, but will be moved out of there in a subsequent patch. Use the __builtin_thread_pointer() helper when available - this will help GCC understand that reloading the value within the same function is not necessary, even when using the per-task stack protector (which also generates accesses via the TLS register). For example, the generated code below loads TPIDRURO only once, and uses it to access both the stack canary and the preempt_count fields. <do_one_initcall>: e92d 41f0 stmdb sp!, {r4, r5, r6, r7, r8, lr} ee1d 4f70 mrc 15, 0, r4, cr13, cr0, {3} 4606 mov r6, r0 b094 sub sp, #80 ; 0x50 f8d4 34e8 ldr.w r3, [r4, #1256] ; 0x4e8 <- stack canary 9313 str r3, [sp, #76] ; 0x4c f8d4 8004 ldr.w r8, [r4, #4] <- preempt count Co-developed-by: Keith Packard <keithpac@amazon.com> Signed-off-by: Keith Packard <keithpac@amazon.com> Signed-off-by: Ard Biesheuvel <ardb@kernel.org> Reviewed-by: Linus Walleij <linus.walleij@linaro.org> Tested-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
2021-09-18 08:44:37 +00:00
/* SPDX-License-Identifier: GPL-2.0-only */
/*
* Copyright (c) 2021 Keith Packard <keithp@keithp.com>
* Copyright (c) 2021 Google, LLC <ardb@kernel.org>
*/
#ifndef _ASM_ARM_CURRENT_H
#define _ASM_ARM_CURRENT_H
#ifndef __ASSEMBLY__
struct task_struct;
static inline void set_current(struct task_struct *cur)
{
if (!IS_ENABLED(CONFIG_CURRENT_POINTER_IN_TPIDRURO))
return;
/* Set TPIDRURO */
asm("mcr p15, 0, %0, c13, c0, 3" :: "r"(cur) : "memory");
}
#ifdef CONFIG_CURRENT_POINTER_IN_TPIDRURO
static inline struct task_struct *get_current(void)
{
struct task_struct *cur;
ARM: 9151/1: Thumb2: avoid __builtin_thread_pointer() on Clang If available, we use the __builtin_thread_pointer() helper to get the value of the TLS register, to help the compiler understand that it doesn't need to reload it every time we access 'current'. Unfortunately, Clang fails to emit the MRC system register read directly when building for Thumb2, and instead, it issues a call to the __aeabi_read_tp helper, which the kernel does not provide, and so this result in link failures at build time. So create a special case for this, and emit the MRC directly using an asm() block, just like we do when the helper is not available to begin with. Link: https://github.com/ClangBuiltLinux/linux/issues/1485 Reviewed-by: Nick Desaulniers <ndesaulniers@google.com> Reviewed-by: Nathan Chancellor <nathan@kernel.org> Tested-by: Nathan Chancellor <nathan@kernel.org> Reviewed-by: Kees Cook <keescook@chromium.org> Signed-off-by: Ard Biesheuvel <ardb@kernel.org> Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
2021-10-29 16:49:37 +00:00
#if __has_builtin(__builtin_thread_pointer) && \
!(defined(CONFIG_THUMB2_KERNEL) && \
defined(CONFIG_CC_IS_CLANG) && CONFIG_CLANG_VERSION < 130001)
ARM: smp: Store current pointer in TPIDRURO register if available Now that the user space TLS register is assigned on every return to user space, we can use it to keep the 'current' pointer while running in the kernel. This removes the need to access it via thread_info, which is located at the base of the stack, but will be moved out of there in a subsequent patch. Use the __builtin_thread_pointer() helper when available - this will help GCC understand that reloading the value within the same function is not necessary, even when using the per-task stack protector (which also generates accesses via the TLS register). For example, the generated code below loads TPIDRURO only once, and uses it to access both the stack canary and the preempt_count fields. <do_one_initcall>: e92d 41f0 stmdb sp!, {r4, r5, r6, r7, r8, lr} ee1d 4f70 mrc 15, 0, r4, cr13, cr0, {3} 4606 mov r6, r0 b094 sub sp, #80 ; 0x50 f8d4 34e8 ldr.w r3, [r4, #1256] ; 0x4e8 <- stack canary 9313 str r3, [sp, #76] ; 0x4c f8d4 8004 ldr.w r8, [r4, #4] <- preempt count Co-developed-by: Keith Packard <keithpac@amazon.com> Signed-off-by: Keith Packard <keithpac@amazon.com> Signed-off-by: Ard Biesheuvel <ardb@kernel.org> Reviewed-by: Linus Walleij <linus.walleij@linaro.org> Tested-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
2021-09-18 08:44:37 +00:00
/*
* Use the __builtin helper when available - this results in better
* code, especially when using GCC in combination with the per-task
* stack protector, as the compiler will recognize that it needs to
* load the TLS register only once in every function.
ARM: 9151/1: Thumb2: avoid __builtin_thread_pointer() on Clang If available, we use the __builtin_thread_pointer() helper to get the value of the TLS register, to help the compiler understand that it doesn't need to reload it every time we access 'current'. Unfortunately, Clang fails to emit the MRC system register read directly when building for Thumb2, and instead, it issues a call to the __aeabi_read_tp helper, which the kernel does not provide, and so this result in link failures at build time. So create a special case for this, and emit the MRC directly using an asm() block, just like we do when the helper is not available to begin with. Link: https://github.com/ClangBuiltLinux/linux/issues/1485 Reviewed-by: Nick Desaulniers <ndesaulniers@google.com> Reviewed-by: Nathan Chancellor <nathan@kernel.org> Tested-by: Nathan Chancellor <nathan@kernel.org> Reviewed-by: Kees Cook <keescook@chromium.org> Signed-off-by: Ard Biesheuvel <ardb@kernel.org> Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
2021-10-29 16:49:37 +00:00
*
* Clang < 13.0.1 gets this wrong for Thumb2 builds:
* https://github.com/ClangBuiltLinux/linux/issues/1485
ARM: smp: Store current pointer in TPIDRURO register if available Now that the user space TLS register is assigned on every return to user space, we can use it to keep the 'current' pointer while running in the kernel. This removes the need to access it via thread_info, which is located at the base of the stack, but will be moved out of there in a subsequent patch. Use the __builtin_thread_pointer() helper when available - this will help GCC understand that reloading the value within the same function is not necessary, even when using the per-task stack protector (which also generates accesses via the TLS register). For example, the generated code below loads TPIDRURO only once, and uses it to access both the stack canary and the preempt_count fields. <do_one_initcall>: e92d 41f0 stmdb sp!, {r4, r5, r6, r7, r8, lr} ee1d 4f70 mrc 15, 0, r4, cr13, cr0, {3} 4606 mov r6, r0 b094 sub sp, #80 ; 0x50 f8d4 34e8 ldr.w r3, [r4, #1256] ; 0x4e8 <- stack canary 9313 str r3, [sp, #76] ; 0x4c f8d4 8004 ldr.w r8, [r4, #4] <- preempt count Co-developed-by: Keith Packard <keithpac@amazon.com> Signed-off-by: Keith Packard <keithpac@amazon.com> Signed-off-by: Ard Biesheuvel <ardb@kernel.org> Reviewed-by: Linus Walleij <linus.walleij@linaro.org> Tested-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
2021-09-18 08:44:37 +00:00
*/
cur = __builtin_thread_pointer();
#else
asm("mrc p15, 0, %0, c13, c0, 3" : "=r"(cur));
#endif
return cur;
}
#define current get_current()
#else
#include <asm-generic/current.h>
#endif /* CONFIG_CURRENT_POINTER_IN_TPIDRURO */
#endif /* __ASSEMBLY__ */
#endif /* _ASM_ARM_CURRENT_H */
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