c1e42efacb
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>
56 lines
1.4 KiB
C
56 lines
1.4 KiB
C
/* SPDX-License-Identifier: GPL-2.0-only */
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/*
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* Copyright (c) 2021 Keith Packard <keithp@keithp.com>
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* Copyright (c) 2021 Google, LLC <ardb@kernel.org>
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*/
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#ifndef _ASM_ARM_CURRENT_H
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#define _ASM_ARM_CURRENT_H
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#ifndef __ASSEMBLY__
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struct task_struct;
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static inline void set_current(struct task_struct *cur)
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{
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if (!IS_ENABLED(CONFIG_CURRENT_POINTER_IN_TPIDRURO))
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return;
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/* Set TPIDRURO */
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asm("mcr p15, 0, %0, c13, c0, 3" :: "r"(cur) : "memory");
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}
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#ifdef CONFIG_CURRENT_POINTER_IN_TPIDRURO
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static inline struct task_struct *get_current(void)
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{
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struct task_struct *cur;
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#if __has_builtin(__builtin_thread_pointer) && \
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!(defined(CONFIG_THUMB2_KERNEL) && \
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defined(CONFIG_CC_IS_CLANG) && CONFIG_CLANG_VERSION < 130001)
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/*
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* Use the __builtin helper when available - this results in better
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* code, especially when using GCC in combination with the per-task
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* stack protector, as the compiler will recognize that it needs to
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* load the TLS register only once in every function.
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*
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* Clang < 13.0.1 gets this wrong for Thumb2 builds:
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* https://github.com/ClangBuiltLinux/linux/issues/1485
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*/
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cur = __builtin_thread_pointer();
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#else
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asm("mrc p15, 0, %0, c13, c0, 3" : "=r"(cur));
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#endif
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return cur;
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}
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#define current get_current()
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#else
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#include <asm-generic/current.h>
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#endif /* CONFIG_CURRENT_POINTER_IN_TPIDRURO */
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#endif /* __ASSEMBLY__ */
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#endif /* _ASM_ARM_CURRENT_H */
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