[PATCH 07/14] KVM: x86: SVM: add warning for CVE-2021-3656

[Maxim Levitsky]

Just in case, add a warning ensuring that on guest entry,
either both VMLOAD and VMSAVE intercept is enabled or
vVMLOAD/VMSAVE is enabled.

Signed-off-by: Maxim Levitsky <mlevitsk@xxxxxxxxxx>
---
 arch/x86/kvm/svm/svm.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 861ac9f74331..deeebd05f682 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -3784,6 +3784,12 @@ static __no_kcsan fastpath_t svm_vcpu_run(struct kvm_vcpu *vcpu)
 
 	WARN_ON_ONCE(kvm_apicv_activated(vcpu->kvm) != kvm_vcpu_apicv_active(vcpu));
 
+	/* Check that CVE-2021-3656 can't happen again */
+	if (!svm_is_intercept(svm, INTERCEPT_VMSAVE) ||
+	    !svm_is_intercept(svm, INTERCEPT_VMSAVE))
+		WARN_ON(!(svm->vmcb->control.virt_ext &
+			  VIRTUAL_VMLOAD_VMSAVE_ENABLE_MASK));
+
 	sync_lapic_to_cr8(vcpu);
 
 	if (unlikely(svm->asid != svm->vmcb->control.asid)) {
-- 
2.26.3