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authorPaolo Bonzini <pbonzini@redhat.com>2020-02-05 16:10:52 +0100
committerPaolo Bonzini <pbonzini@redhat.com>2020-02-05 16:12:57 +0100
commitdf7e8818926eb4712b67421442acf7d568fe2645 (patch)
tree7eb436326517e289dcb475d119933faace074c97 /arch
parent4400cf546b4bb62d49198f6642add01bf6e9b34d (diff)
downloadlinux-df7e8818926eb4712b67421442acf7d568fe2645.tar.bz2
KVM: SVM: relax conditions for allowing MSR_IA32_SPEC_CTRL accesses
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 <zhguo@redhat.com> Analyzed-by: Dr. David Alan Gilbert <dgilbert@redhat.com> Analyzed-by: Laszlo Ersek <lersek@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'arch')
-rw-r--r--arch/x86/kvm/svm.c4
1 files changed, 4 insertions, 0 deletions
diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index bf0556588ad0..a3e32d61d60c 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -4225,6 +4225,8 @@ 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;
@@ -4310,6 +4312,8 @@ 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;