KVM: x86: fix CR8 handling

The handling of CR8 writes in KVM is currently somewhat cumbersome.
This patch makes it look like the other CR register handlers
and fixes a possible issue in VMX, where the RIP would be incremented
despite an injected #GP.
Signed-off-by: Andre Przywara <andre.przywara@amd.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

arch/x86/include/asm/kvm_host.h

@@ -661,7 +661,7 @@ int kvm_task_switch(struct kvm_vcpu *vcpu, u16 tss_selector, int reason,
 int kvm_set_cr0(struct kvm_vcpu *vcpu, unsigned long cr0);
 int kvm_set_cr3(struct kvm_vcpu *vcpu, unsigned long cr3);
 int kvm_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4);
-void kvm_set_cr8(struct kvm_vcpu *vcpu, unsigned long cr8);
+int kvm_set_cr8(struct kvm_vcpu *vcpu, unsigned long cr8);
 int kvm_set_dr(struct kvm_vcpu *vcpu, int dr, unsigned long val);
 int kvm_get_dr(struct kvm_vcpu *vcpu, int dr, unsigned long *val);
 unsigned long kvm_get_cr8(struct kvm_vcpu *vcpu);

arch/x86/kvm/svm.c

@@ -2676,16 +2676,17 @@ static int cr0_write_interception(struct vcpu_svm *svm)
 static int cr8_write_interception(struct vcpu_svm *svm)
 {
 	struct kvm_run *kvm_run = svm->vcpu.run;
+	int r;
 
 	u8 cr8_prev = kvm_get_cr8(&svm->vcpu);
 	/* instruction emulation calls kvm_set_cr8() */
-	emulate_instruction(&svm->vcpu, 0, 0, 0);
+	r = emulate_instruction(&svm->vcpu, 0, 0, 0);
 	if (irqchip_in_kernel(svm->vcpu.kvm)) {
 		clr_cr_intercept(svm, INTERCEPT_CR8_WRITE);
-		return 1;
+		return r == EMULATE_DONE;
 	}
 	if (cr8_prev <= kvm_get_cr8(&svm->vcpu))
-		return 1;
+		return r == EMULATE_DONE;
 	kvm_run->exit_reason = KVM_EXIT_SET_TPR;
 	return 0;
 }

arch/x86/kvm/vmx.c

@@ -3185,8 +3185,8 @@ static int handle_cr(struct kvm_vcpu *vcpu)
 		case 8: {
 				u8 cr8_prev = kvm_get_cr8(vcpu);
 				u8 cr8 = kvm_register_read(vcpu, reg);
-				kvm_set_cr8(vcpu, cr8);
-				skip_emulated_instruction(vcpu);
+				err = kvm_set_cr8(vcpu, cr8);
+				complete_insn_gp(vcpu, err);
 				if (irqchip_in_kernel(vcpu->kvm))
 					return 1;
 				if (cr8_prev <= cr8)

arch/x86/kvm/x86.c

@@ -662,7 +662,7 @@ int kvm_set_cr3(struct kvm_vcpu *vcpu, unsigned long cr3)
 }
 EXPORT_SYMBOL_GPL(kvm_set_cr3);
 
-int __kvm_set_cr8(struct kvm_vcpu *vcpu, unsigned long cr8)
+int kvm_set_cr8(struct kvm_vcpu *vcpu, unsigned long cr8)
 {
 	if (cr8 & CR8_RESERVED_BITS)
 		return 1;
@@ -672,12 +672,6 @@ int __kvm_set_cr8(struct kvm_vcpu *vcpu, unsigned long cr8)
 		vcpu->arch.cr8 = cr8;
 	return 0;
 }
-
-void kvm_set_cr8(struct kvm_vcpu *vcpu, unsigned long cr8)
-{
-	if (__kvm_set_cr8(vcpu, cr8))
-		kvm_inject_gp(vcpu, 0);
-}
 EXPORT_SYMBOL_GPL(kvm_set_cr8);
 
 unsigned long kvm_get_cr8(struct kvm_vcpu *vcpu)
@@ -4104,7 +4098,7 @@ static int emulator_set_cr(int cr, unsigned long val, struct kvm_vcpu *vcpu)
 		res = kvm_set_cr4(vcpu, mk_cr_64(kvm_read_cr4(vcpu), val));
 		break;
 	case 8:
-		res = __kvm_set_cr8(vcpu, val & 0xfUL);
+		res = kvm_set_cr8(vcpu, val);
 		break;
 	default:
 		vcpu_printf(vcpu, "%s: unexpected cr %u\n", __func__, cr);
@@ -5381,8 +5375,12 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
 	}
 
 	/* re-sync apic's tpr */
-	if (!irqchip_in_kernel(vcpu->kvm))
-		kvm_set_cr8(vcpu, kvm_run->cr8);
+	if (!irqchip_in_kernel(vcpu->kvm)) {
+		if (kvm_set_cr8(vcpu, kvm_run->cr8) != 0) {
+			r = -EINVAL;
+			goto out;
+		}
+	}
 
 	if (vcpu->arch.pio.count || vcpu->mmio_needed) {
 		if (vcpu->mmio_needed) {