@@ -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 +761,12 @@ 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);
+ if (boot_cpu_has(X86_FEATURE_SPEC_CTRL) &&
+ !boot_cpu_has_bug(X86_BUG_EIBRS_PBRSB))
+ 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))
From Intel's documention [1], "CPUID.(EAX=07H,ECX=0):EDX[26] enumerates support for indirect branch restricted speculation (IBRS) and the indirect branch predictor barrier (IBPB)." Further, from [2], "Software that executed before the IBPB command cannot control the predicted targets of indirect branches (4) executed after the command on the same logical processor," where footnote 4 reads, "Note that indirect branches include near call indirect, near jump indirect and near return instructions. Because it includes near returns, it follows that **RSB entries created before an IBPB command cannot control the predicted targets of returns executed after the command on the same logical processor.**" [emphasis mine] 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@chromium.org> Signed-off-by: Jim Mattson <jmattson@google.com> --- arch/x86/kvm/cpuid.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-)