From 80e4c1cd42fff110bfdae8fce7ac4f22465f9664 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Thu, 15 Sep 2022 13:11:19 +0200 Subject: x86/retbleed: Add X86_FEATURE_CALL_DEPTH Intel SKL CPUs fall back to other predictors when the RSB underflows. The only microcode mitigation is IBRS which is insanely expensive. It comes with performance drops of up to 30% depending on the workload. A way less expensive, but nevertheless horrible mitigation is to track the call depth in software and overeagerly fill the RSB when returns underflow the software counter. Provide a configuration symbol and a CPU misfeature bit. Signed-off-by: Thomas Gleixner Signed-off-by: Peter Zijlstra (Intel) Link: https://lore.kernel.org/r/20220915111147.056176424@infradead.org --- arch/x86/include/asm/cpufeatures.h | 1 + arch/x86/include/asm/disabled-features.h | 9 ++++++++- 2 files changed, 9 insertions(+), 1 deletion(-) (limited to 'arch/x86/include') diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h index b71f4f2ecdd5..aefd0816a333 100644 --- a/arch/x86/include/asm/cpufeatures.h +++ b/arch/x86/include/asm/cpufeatures.h @@ -304,6 +304,7 @@ #define X86_FEATURE_UNRET (11*32+15) /* "" AMD BTB untrain return */ #define X86_FEATURE_USE_IBPB_FW (11*32+16) /* "" Use IBPB during runtime firmware calls */ #define X86_FEATURE_RSB_VMEXIT_LITE (11*32+17) /* "" Fill RSB on VM exit when EIBRS is enabled */ +#define X86_FEATURE_CALL_DEPTH (11*32+18) /* "" Call depth tracking for RSB stuffing */ /* Intel-defined CPU features, CPUID level 0x00000007:1 (EAX), word 12 */ #define X86_FEATURE_AVX_VNNI (12*32+ 4) /* AVX VNNI instructions */ diff --git a/arch/x86/include/asm/disabled-features.h b/arch/x86/include/asm/disabled-features.h index 33d2cd04d254..bbb03b25263e 100644 --- a/arch/x86/include/asm/disabled-features.h +++ b/arch/x86/include/asm/disabled-features.h @@ -69,6 +69,12 @@ # define DISABLE_UNRET (1 << (X86_FEATURE_UNRET & 31)) #endif +#ifdef CONFIG_CALL_DEPTH_TRACKING +# define DISABLE_CALL_DEPTH_TRACKING 0 +#else +# define DISABLE_CALL_DEPTH_TRACKING (1 << (X86_FEATURE_CALL_DEPTH & 31)) +#endif + #ifdef CONFIG_INTEL_IOMMU_SVM # define DISABLE_ENQCMD 0 #else @@ -101,7 +107,8 @@ #define DISABLED_MASK8 (DISABLE_TDX_GUEST) #define DISABLED_MASK9 (DISABLE_SGX) #define DISABLED_MASK10 0 -#define DISABLED_MASK11 (DISABLE_RETPOLINE|DISABLE_RETHUNK|DISABLE_UNRET) +#define DISABLED_MASK11 (DISABLE_RETPOLINE|DISABLE_RETHUNK|DISABLE_UNRET| \ + DISABLE_CALL_DEPTH_TRACKING) #define DISABLED_MASK12 0 #define DISABLED_MASK13 0 #define DISABLED_MASK14 0 -- cgit v1.2.3