3.16.56-rc1 review patch. If anyone has any objections, please let me know.
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From: Dan Williams dan.j.williams@intel.com
commit b3d7ad85b80bbc404635dca80f5b129f6242bc7a upstream.
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 torvalds@linux-foundation.org Suggested-by: Andi Kleen ak@linux.intel.com Suggested-by: Ingo Molnar mingo@redhat.com Signed-off-by: Dan Williams dan.j.williams@intel.com Signed-off-by: Thomas Gleixner tglx@linutronix.de Cc: linux-arch@vger.kernel.org Cc: Tom Lendacky thomas.lendacky@amd.com Cc: Kees Cook keescook@chromium.org Cc: kernel-hardening@lists.openwall.com Cc: gregkh@linuxfoundation.org Cc: Al Viro viro@zeniv.linux.org.uk Cc: alan@linux.intel.com Link: https://lkml.kernel.org/r/151727415361.33451.9049453007262764675.stgit@dwill... [bwh: Backported to 3.16: update rdtsc_barrier() instead of rdtsc_ordered()] Signed-off-by: Ben Hutchings ben@decadent.org.uk --- --- a/arch/x86/include/asm/barrier.h +++ b/arch/x86/include/asm/barrier.h @@ -48,6 +48,10 @@ static inline unsigned long array_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) + /** * read_barrier_depends - Flush all pending reads that subsequents reads * depend on. @@ -174,8 +178,7 @@ do { \ */ static __always_inline void rdtsc_barrier(void) { - alternative(ASM_NOP3, "mfence", X86_FEATURE_MFENCE_RDTSC); - alternative(ASM_NOP3, "lfence", X86_FEATURE_LFENCE_RDTSC); + barrier_nospec(); }
#endif /* _ASM_X86_BARRIER_H */