From: Paolo Bonzini Date: Wed, 5 Feb 2020 15:10:52 +0000 (+0100) Subject: KVM: SVM: relax conditions for allowing MSR_IA32_SPEC_CTRL accesses X-Git-Tag: v4.19.165~21 X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=88464279c03ce05b56abeed7c38c4064dd054ab9;p=users%2Fdwmw2%2Flinux.git KVM: SVM: relax conditions for allowing MSR_IA32_SPEC_CTRL accesses [ Upstream commit df7e8818926eb4712b67421442acf7d568fe2645 ] Userspace that does not know about the AMD_IBRS bit might still allow the guest to protect itself with MSR_IA32_SPEC_CTRL using the Intel SPEC_CTRL bit. However, svm.c disallows this and will cause a #GP in the guest when writing to the MSR. Fix this by loosening the test and allowing the Intel CPUID bit, and in fact allow the AMD_STIBP bit as well since it allows writing to MSR_IA32_SPEC_CTRL too. Reported-by: Zhiyi Guo Analyzed-by: Dr. David Alan Gilbert Analyzed-by: Laszlo Ersek Signed-off-by: Paolo Bonzini Signed-off-by: Sasha Levin --- diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c index a0c3d1b4b295b..f513110983d4c 100644 --- a/arch/x86/kvm/svm.c +++ b/arch/x86/kvm/svm.c @@ -4209,6 +4209,8 @@ static int svm_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info) break; case MSR_IA32_SPEC_CTRL: if (!msr_info->host_initiated && + !guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL) && + !guest_cpuid_has(vcpu, X86_FEATURE_AMD_STIBP) && !guest_cpuid_has(vcpu, X86_FEATURE_AMD_IBRS) && !guest_cpuid_has(vcpu, X86_FEATURE_AMD_SSBD)) return 1; @@ -4312,6 +4314,8 @@ static int svm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr) break; case MSR_IA32_SPEC_CTRL: if (!msr->host_initiated && + !guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL) && + !guest_cpuid_has(vcpu, X86_FEATURE_AMD_STIBP) && !guest_cpuid_has(vcpu, X86_FEATURE_AMD_IBRS) && !guest_cpuid_has(vcpu, X86_FEATURE_AMD_SSBD)) return 1;