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.
There are no functional changes in this patch.
Suggested-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Suggested-by: Andi Kleen <ak@xxxxxxxxxxxxxxx>
Suggested-by: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Tom Lendacky <thomas.lendacky@xxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: x86@xxxxxxxxxx
Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
---
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 551ccbe07c0f..1e7c955b6303 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 07962f5f6fba..30df295f6d94 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();
}
