From: Dan Williams Date: Tue, 30 Jan 2018 01:02:33 +0000 (-0800) Subject: x86: Introduce barrier_nospec X-Git-Tag: v3.2.101~20 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=507089d2b9540f698a9b8648207da02edeedfcf0;p=thirdparty%2Fkernel%2Fstable.git x86: Introduce barrier_nospec 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 Suggested-by: Andi Kleen Suggested-by: Ingo Molnar Signed-off-by: Dan Williams Signed-off-by: Thomas Gleixner Cc: linux-arch@vger.kernel.org Cc: Tom Lendacky Cc: Kees Cook Cc: kernel-hardening@lists.openwall.com Cc: gregkh@linuxfoundation.org Cc: Al Viro Cc: alan@linux.intel.com Link: https://lkml.kernel.org/r/151727415361.33451.9049453007262764675.stgit@dwillia2-desk3.amr.corp.intel.com [bwh: Backported to 3.2: update rdtsc_barrier() instead of rdtsc_ordered()] Signed-off-by: Ben Hutchings --- diff --git a/arch/x86/include/asm/system.h b/arch/x86/include/asm/system.h index 41fda4d8710c0..59567d16c6175 100644 --- a/arch/x86/include/asm/system.h +++ b/arch/x86/include/asm/system.h @@ -478,6 +478,10 @@ 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) + /** * read_barrier_depends - Flush all pending reads that subsequents reads * depend on. @@ -563,8 +567,7 @@ static inline unsigned long array_index_mask_nospec(unsigned long index, */ 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(); } /*