KVM: SVM: Prevent debugging under SEV-ES

Since the guest register state of an SEV-ES guest is encrypted, debugging
is not supported. Update the code to prevent guest debugging when the
guest has protected state.

Additionally, an SEV-ES guest must only and always intercept DR7 reads and
writes. Update set_dr_intercepts() and clr_dr_intercepts() to account for
this.
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Message-Id: <8db966fa2f9803d6454ce773863025d0e2e7f3cc.1607620209.git.thomas.lendacky@amd.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/svm/svm.c

@@ -1805,6 +1805,9 @@ static void svm_set_dr6(struct vcpu_svm *svm, unsigned long value)
 {
 	struct vmcb *vmcb = svm->vmcb;
 
+	if (svm->vcpu.arch.guest_state_protected)
+		return;
+
 	if (unlikely(value != vmcb->save.dr6)) {
 		vmcb->save.dr6 = value;
 		vmcb_mark_dirty(vmcb, VMCB_DR);
@@ -1815,6 +1818,9 @@ static void svm_sync_dirty_debug_regs(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_svm *svm = to_svm(vcpu);
 
+	if (vcpu->arch.guest_state_protected)
+		return;
+
 	get_debugreg(vcpu->arch.db[0], 0);
 	get_debugreg(vcpu->arch.db[1], 1);
 	get_debugreg(vcpu->arch.db[2], 2);
@@ -1833,6 +1839,9 @@ static void svm_set_dr7(struct kvm_vcpu *vcpu, unsigned long value)
 {
 	struct vcpu_svm *svm = to_svm(vcpu);
 
+	if (vcpu->arch.guest_state_protected)
+		return;
+
 	svm->vmcb->save.dr7 = value;
 	vmcb_mark_dirty(svm->vmcb, VMCB_DR);
 }

arch/x86/kvm/svm/svm.h

@@ -272,21 +272,24 @@ static inline void set_dr_intercepts(struct vcpu_svm *svm)
 {
 	struct vmcb *vmcb = get_host_vmcb(svm);
 
-	vmcb_set_intercept(&vmcb->control, INTERCEPT_DR0_READ);
-	vmcb_set_intercept(&vmcb->control, INTERCEPT_DR1_READ);
-	vmcb_set_intercept(&vmcb->control, INTERCEPT_DR2_READ);
-	vmcb_set_intercept(&vmcb->control, INTERCEPT_DR3_READ);
-	vmcb_set_intercept(&vmcb->control, INTERCEPT_DR4_READ);
-	vmcb_set_intercept(&vmcb->control, INTERCEPT_DR5_READ);
-	vmcb_set_intercept(&vmcb->control, INTERCEPT_DR6_READ);
+	if (!sev_es_guest(svm->vcpu.kvm)) {
+		vmcb_set_intercept(&vmcb->control, INTERCEPT_DR0_READ);
+		vmcb_set_intercept(&vmcb->control, INTERCEPT_DR1_READ);
+		vmcb_set_intercept(&vmcb->control, INTERCEPT_DR2_READ);
+		vmcb_set_intercept(&vmcb->control, INTERCEPT_DR3_READ);
+		vmcb_set_intercept(&vmcb->control, INTERCEPT_DR4_READ);
+		vmcb_set_intercept(&vmcb->control, INTERCEPT_DR5_READ);
+		vmcb_set_intercept(&vmcb->control, INTERCEPT_DR6_READ);
+		vmcb_set_intercept(&vmcb->control, INTERCEPT_DR0_WRITE);
+		vmcb_set_intercept(&vmcb->control, INTERCEPT_DR1_WRITE);
+		vmcb_set_intercept(&vmcb->control, INTERCEPT_DR2_WRITE);
+		vmcb_set_intercept(&vmcb->control, INTERCEPT_DR3_WRITE);
+		vmcb_set_intercept(&vmcb->control, INTERCEPT_DR4_WRITE);
+		vmcb_set_intercept(&vmcb->control, INTERCEPT_DR5_WRITE);
+		vmcb_set_intercept(&vmcb->control, INTERCEPT_DR6_WRITE);
+	}
+
 	vmcb_set_intercept(&vmcb->control, INTERCEPT_DR7_READ);
-	vmcb_set_intercept(&vmcb->control, INTERCEPT_DR0_WRITE);
-	vmcb_set_intercept(&vmcb->control, INTERCEPT_DR1_WRITE);
-	vmcb_set_intercept(&vmcb->control, INTERCEPT_DR2_WRITE);
-	vmcb_set_intercept(&vmcb->control, INTERCEPT_DR3_WRITE);
-	vmcb_set_intercept(&vmcb->control, INTERCEPT_DR4_WRITE);
-	vmcb_set_intercept(&vmcb->control, INTERCEPT_DR5_WRITE);
-	vmcb_set_intercept(&vmcb->control, INTERCEPT_DR6_WRITE);
 	vmcb_set_intercept(&vmcb->control, INTERCEPT_DR7_WRITE);
 
 	recalc_intercepts(svm);
@@ -298,6 +301,12 @@ static inline void clr_dr_intercepts(struct vcpu_svm *svm)
 
 	vmcb->control.intercepts[INTERCEPT_DR] = 0;
 
+	/* DR7 access must remain intercepted for an SEV-ES guest */
+	if (sev_es_guest(svm->vcpu.kvm)) {
+		vmcb_set_intercept(&vmcb->control, INTERCEPT_DR7_READ);
+		vmcb_set_intercept(&vmcb->control, INTERCEPT_DR7_WRITE);
+	}
+
 	recalc_intercepts(svm);
 }
 

arch/x86/kvm/x86.c

@@ -9664,6 +9664,9 @@ int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu *vcpu,
 	unsigned long rflags;
 	int i, r;
 
+	if (vcpu->arch.guest_state_protected)
+		return -EINVAL;
+
 	vcpu_load(vcpu);
 
 	if (dbg->control & (KVM_GUESTDBG_INJECT_DB | KVM_GUESTDBG_INJECT_BP)) {