[PATCH 1/3] KVM: SVM: Check EFER.SVME before updating MSR_VM_CR on guest writes

[Jim Mattson <jmattson@google.com>]

Per the AMD APM, setting VM_CR.SVMDIS while EFER.SVME is set raises a #GP.

In svm_set_vm_cr(), check whether EFER.SVME is set and the value being
written sets SVMDIS *before* modifying svm->nested.vm_cr_msr. (Host-
initiated writes are allowed to set any valid MSR_VM_CR bits.)

Fixes: 4a810181c8bc ("KVM: SVM: Implement emulation of vm_cr msr")
Signed-off-by: Jim Mattson <jmattson@google.com>
---
 arch/x86/kvm/svm/svm.c | 22 +++++++++++++---------
 1 file changed, 13 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 136069dfcd44..3a0a507c94b2 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -3015,14 +3015,24 @@ static int svm_complete_emulated_msr(struct kvm_vcpu *vcpu, int err)
 	return 1;
 }
 
-static int svm_set_vm_cr(struct kvm_vcpu *vcpu, u64 data)
+static int svm_set_vm_cr(struct kvm_vcpu *vcpu, struct msr_data *msr)
 {
 	struct vcpu_svm *svm = to_svm(vcpu);
-	int svm_dis, chg_mask;
+	u64 data = msr->data;
+	int chg_mask;
 
 	if (data & ~SVM_VM_CR_VALID_MASK)
 		return 1;
 
+	if (msr->host_initiated) {
+		svm->nested.vm_cr_msr = data;
+		return 0;
+	}
+
+	/* check for svm_disable while efer.svme is set */
+	if ((data & SVM_VM_CR_SVM_DIS_MASK) && (vcpu->arch.efer & EFER_SVME))
+		return 1;
+
 	chg_mask = SVM_VM_CR_VALID_MASK;
 
 	if (svm->nested.vm_cr_msr & SVM_VM_CR_SVM_DIS_MASK)
@@ -3031,12 +3041,6 @@ static int svm_set_vm_cr(struct kvm_vcpu *vcpu, u64 data)
 	svm->nested.vm_cr_msr &= ~chg_mask;
 	svm->nested.vm_cr_msr |= (data & chg_mask);
 
-	svm_dis = svm->nested.vm_cr_msr & SVM_VM_CR_SVM_DIS_MASK;
-
-	/* check for svm_disable while efer.svme is set */
-	if (svm_dis && (vcpu->arch.efer & EFER_SVME))
-		return 1;
-
 	return 0;
 }
 
@@ -3262,7 +3266,7 @@ static int svm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr)
 		svm->nested.hsave_msr = data & PAGE_MASK;
 		break;
 	case MSR_VM_CR:
-		return svm_set_vm_cr(vcpu, data);
+		return svm_set_vm_cr(vcpu, msr);
 	case MSR_VM_IGNNE:
 		kvm_pr_unimpl_wrmsr(vcpu, ecx, data);
 		break;
-- 
2.56.0.317.g454f8302e1-goog