On the other hand, AMD's IBPB "may not prevent return branch predictions from being specified by pre-IBPB branch targets" [3]. However, some AMD processors have an "enhanced IBPB" [terminology mine] which does clear the return address predictor. This feature is enumerated by CPUID.80000008:EDX.IBPB_RET[bit 30] [4]. Adjust the cross-vendor features enumerated by KVM_GET_SUPPORTED_CPUID accordingly. [1] https://www.intel.com/content/www/us/en/developer/articles/technical/software-security-guidance/technical-documentation/cpuid-enumeration-and-architectural-msrs.html [2] https://www.intel.com/content/www/us/en/developer/articles/technical/software-security-guidance/technical-documentation/speculative-execution-side-channel-mitigations.html#Footnotes [3] https://www.amd.com/en/resources/product-security/bulletin/amd-sb-1040.html [4] https://www.amd.com/content/dam/amd/en/documents/processor-tech-docs/programmer-references/24594.pdf Fixes: 0c54914d0c52 ("KVM: x86: use Intel speculation bugs and features as derived in generic x86 code") Suggested-by: Venkatesh Srinivas <venkateshs@xxxxxxxxxxxx> Signed-off-by: Jim Mattson <jmattson@xxxxxxxxxx> --- v2: Use IBPB_RET to identify semantic equality (Venkatesh) arch/x86/kvm/cpuid.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c index 2617be544480..044bdc9e938b 100644 --- a/arch/x86/kvm/cpuid.c +++ b/arch/x86/kvm/cpuid.c @@ -690,7 +690,9 @@ void kvm_set_cpu_caps(void) kvm_cpu_cap_set(X86_FEATURE_TSC_ADJUST); kvm_cpu_cap_set(X86_FEATURE_ARCH_CAPABILITIES); - if (boot_cpu_has(X86_FEATURE_IBPB) && boot_cpu_has(X86_FEATURE_IBRS)) + if (boot_cpu_has(X86_FEATURE_AMD_IBPB_RET) && + boot_cpu_has(X86_FEATURE_AMD_IBPB) && + boot_cpu_has(X86_FEATURE_AMD_IBRS)) kvm_cpu_cap_set(X86_FEATURE_SPEC_CTRL); if (boot_cpu_has(X86_FEATURE_STIBP)) kvm_cpu_cap_set(X86_FEATURE_INTEL_STIBP); @@ -759,8 +761,10 @@ void kvm_set_cpu_caps(void) * arch/x86/kernel/cpu/bugs.c is kind enough to * record that in cpufeatures so use them. */ - if (boot_cpu_has(X86_FEATURE_IBPB)) + if (boot_cpu_has(X86_FEATURE_IBPB)) { kvm_cpu_cap_set(X86_FEATURE_AMD_IBPB); + kvm_cpu_cap_set(X86_FEATURE_AMD_IBPB_RET); + } if (boot_cpu_has(X86_FEATURE_IBRS)) kvm_cpu_cap_set(X86_FEATURE_AMD_IBRS); if (boot_cpu_has(X86_FEATURE_STIBP)) -- 2.46.0.184.g6999bdac58-goog
