Commit-ID: b3d7ad85b80bbc404635dca80f5b129f6242bc7a Gitweb: https://git.kernel.org/tip/b3d7ad85b80bbc404635dca80f5b129f6242bc7a Author: Dan Williams <[email protected]> AuthorDate: Mon, 29 Jan 2018 17:02:33 -0800 Committer: Thomas Gleixner <[email protected]> CommitDate: Tue, 30 Jan 2018 21:54:29 +0100
x86: Introduce barrier_nospec Rename the open coded form of this instruction sequence from rdtsc_ordered() into a generic barrier primitive, barrier_nospec(). One of the mitigations for Spectre variant1 vulnerabilities is to fence speculative execution after successfully validating a bounds check. I.e. force the result of a bounds check to resolve in the instruction pipeline to ensure speculative execution honors that result before potentially operating on out-of-bounds data. No functional changes. Suggested-by: Linus Torvalds <[email protected]> Suggested-by: Andi Kleen <[email protected]> Suggested-by: Ingo Molnar <[email protected]> Signed-off-by: Dan Williams <[email protected]> Signed-off-by: Thomas Gleixner <[email protected]> Cc: [email protected] Cc: Tom Lendacky <[email protected]> Cc: Kees Cook <[email protected]> Cc: [email protected] Cc: [email protected] Cc: Al Viro <[email protected]> Cc: [email protected] Link: https://lkml.kernel.org/r/151727415361.33451.9049453007262764675.st...@dwillia2-desk3.amr.corp.intel.com --- arch/x86/include/asm/barrier.h | 4 ++++ arch/x86/include/asm/msr.h | 3 +-- 2 files changed, 5 insertions(+), 2 deletions(-) diff --git a/arch/x86/include/asm/barrier.h b/arch/x86/include/asm/barrier.h index 173b38f..30d4061 100644 --- a/arch/x86/include/asm/barrier.h +++ b/arch/x86/include/asm/barrier.h @@ -48,6 +48,10 @@ static inline unsigned long array_index_mask_nospec(unsigned long index, /* Override the default implementation from linux/nospec.h. */ #define array_index_mask_nospec array_index_mask_nospec +/* Prevent speculative execution past this barrier. */ +#define barrier_nospec() alternative_2("", "mfence", X86_FEATURE_MFENCE_RDTSC, \ + "lfence", X86_FEATURE_LFENCE_RDTSC) + #ifdef CONFIG_X86_PPRO_FENCE #define dma_rmb() rmb() #else diff --git a/arch/x86/include/asm/msr.h b/arch/x86/include/asm/msr.h index 07962f5..30df295 100644 --- a/arch/x86/include/asm/msr.h +++ b/arch/x86/include/asm/msr.h @@ -214,8 +214,7 @@ static __always_inline unsigned long long rdtsc_ordered(void) * that some other imaginary CPU is updating continuously with a * time stamp. */ - alternative_2("", "mfence", X86_FEATURE_MFENCE_RDTSC, - "lfence", X86_FEATURE_LFENCE_RDTSC); + barrier_nospec(); return rdtsc(); }
