From: Sean Christopherson Date: Fri, 2 Aug 2024 18:19:26 +0000 (-0700) Subject: KVM: SVM: Disallow guest from changing userspace's MSR_AMD64_DE_CFG value X-Git-Tag: v6.12-rc1~11^2~6^2~26 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=74a0e79df68a8042fb84fd7207e57b70722cf825;p=thirdparty%2Fkernel%2Fstable.git KVM: SVM: Disallow guest from changing userspace's MSR_AMD64_DE_CFG value 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 Reviewed-by: Tom Lendacky Link: https://lore.kernel.org/r/20240802181935.292540-2-seanjc@google.com Signed-off-by: Sean Christopherson --- diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c index d6f252555ab3f..eaa41a6a00ee6 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 capabilities. + */ + if (!msr->host_initiated && data != svm->msr_decfg) return 1; svm->msr_decfg = data;