| Message ID | 20240802181935.292540-2-seanjc@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | KVM: x86: Clean up MSR access/failure handling | expand |
On 8/2/24 13:19, Sean Christopherson wrote: > Inject a #GP if the guest attempts to change MSR_AMD64_DE_CFG from its > *current* value, not if the guest attempts to write a value other than > KVM's set of supported bits. As per the comment and the changelog of the > original code, the intent is to effectively make MSR_AMD64_DE_CFG read- > only for the guest. > > Opportunistically use a more conventional equality check instead of an > exclusive-OR check to detect attempts to change bits. > > Fixes: d1d93fa90f1a ("KVM: SVM: Add MSR-based feature support for serializing LFENCE") > Cc: Tom Lendacky <thomas.lendacky@amd.com> > Signed-off-by: Sean Christopherson <seanjc@google.com> Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com> (one spelling correction below) > --- > arch/x86/kvm/svm/svm.c | 9 +++++++-- > 1 file changed, 7 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c > index c115d26844f7..550ead197543 100644 > --- a/arch/x86/kvm/svm/svm.c > +++ b/arch/x86/kvm/svm/svm.c > @@ -3189,8 +3189,13 @@ static int svm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr) > if (data & ~msr_entry.data) > return 1; > > - /* Don't allow the guest to change a bit, #GP */ > - if (!msr->host_initiated && (data ^ msr_entry.data)) > + /* > + * Don't let the guest change the host-programmed value. The > + * MSR is very model specific, i.e. contains multiple bits that > + * are completely unknown to KVM, and the one bit known to KVM > + * is simply a reflection of hardware capatibilies. s/capatibilies/capabilities/ > + */ > + if (!msr->host_initiated && data != svm->msr_decfg) > return 1; > > svm->msr_decfg = data;
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c index c115d26844f7..550ead197543 100644 --- a/arch/x86/kvm/svm/svm.c +++ b/arch/x86/kvm/svm/svm.c @@ -3189,8 +3189,13 @@ static int svm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr) if (data & ~msr_entry.data) return 1; - /* Don't allow the guest to change a bit, #GP */ - if (!msr->host_initiated && (data ^ msr_entry.data)) + /* + * Don't let the guest change the host-programmed value. The + * MSR is very model specific, i.e. contains multiple bits that + * are completely unknown to KVM, and the one bit known to KVM + * is simply a reflection of hardware capatibilies. + */ + if (!msr->host_initiated && data != svm->msr_decfg) return 1; svm->msr_decfg = data;
Inject a #GP if the guest attempts to change MSR_AMD64_DE_CFG from its *current* value, not if the guest attempts to write a value other than KVM's set of supported bits. As per the comment and the changelog of the original code, the intent is to effectively make MSR_AMD64_DE_CFG read- only for the guest. Opportunistically use a more conventional equality check instead of an exclusive-OR check to detect attempts to change bits. Fixes: d1d93fa90f1a ("KVM: SVM: Add MSR-based feature support for serializing LFENCE") Cc: Tom Lendacky <thomas.lendacky@amd.com> Signed-off-by: Sean Christopherson <seanjc@google.com> --- arch/x86/kvm/svm/svm.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-)