KVM: x86 emulator: make (get|set)_dr() callback return error if it fails

Make (get|set)_dr() callback return error if it fails instead of
injecting exception behind emulator's back.
Signed-off-by: NGleb Natapov <gleb@redhat.com>
Signed-off-by: NAvi Kivity <avi@redhat.com>

arch/x86/kvm/emulate.c

@@ -3151,9 +3151,14 @@ x86_emulate_insn(struct x86_emulate_ctxt *ctxt, struct x86_emulate_ops *ops)
 			goto done;
 		}
 
-		ops->set_dr(c->modrm_reg,c->regs[c->modrm_rm] &
-			    ((ctxt->mode == X86EMUL_MODE_PROT64) ? ~0ULL : ~0U),
-			ctxt->vcpu);
+		if (ops->set_dr(c->modrm_reg, c->regs[c->modrm_rm] &
+				((ctxt->mode == X86EMUL_MODE_PROT64) ?
+				 ~0ULL : ~0U), ctxt->vcpu) < 0) {
+			/* #UD condition is already handled by the code above */
+			kvm_inject_gp(ctxt->vcpu, 0);
+			goto done;
+		}
+
 		c->dst.type = OP_NONE;	/* no writeback */
 		break;
 	case 0x30:

arch/x86/kvm/x86.c

@@ -573,7 +573,7 @@ unsigned long kvm_get_cr8(struct kvm_vcpu *vcpu)
 }
 EXPORT_SYMBOL_GPL(kvm_get_cr8);
 
-int kvm_set_dr(struct kvm_vcpu *vcpu, int dr, unsigned long val)
+static int __kvm_set_dr(struct kvm_vcpu *vcpu, int dr, unsigned long val)
 {
 	switch (dr) {
 	case 0 ... 3:
@@ -582,29 +582,21 @@ int kvm_set_dr(struct kvm_vcpu *vcpu, int dr, unsigned long val)
 			vcpu->arch.eff_db[dr] = val;
 		break;
 	case 4:
-		if (kvm_read_cr4_bits(vcpu, X86_CR4_DE)) {
-			kvm_queue_exception(vcpu, UD_VECTOR);
-			return 1;
-		}
+		if (kvm_read_cr4_bits(vcpu, X86_CR4_DE))
+			return 1; /* #UD */
 		/* fall through */
 	case 6:
-		if (val & 0xffffffff00000000ULL) {
-			kvm_inject_gp(vcpu, 0);
-			return 1;
-		}
+		if (val & 0xffffffff00000000ULL)
+			return -1; /* #GP */
 		vcpu->arch.dr6 = (val & DR6_VOLATILE) | DR6_FIXED_1;
 		break;
 	case 5:
-		if (kvm_read_cr4_bits(vcpu, X86_CR4_DE)) {
-			kvm_queue_exception(vcpu, UD_VECTOR);
-			return 1;
-		}
+		if (kvm_read_cr4_bits(vcpu, X86_CR4_DE))
+			return 1; /* #UD */
 		/* fall through */
 	default: /* 7 */
-		if (val & 0xffffffff00000000ULL) {
-			kvm_inject_gp(vcpu, 0);
-			return 1;
-		}
+		if (val & 0xffffffff00000000ULL)
+			return -1; /* #GP */
 		vcpu->arch.dr7 = (val & DR7_VOLATILE) | DR7_FIXED_1;
 		if (!(vcpu->guest_debug & KVM_GUESTDBG_USE_HW_BP)) {
 			kvm_x86_ops->set_dr7(vcpu, vcpu->arch.dr7);
@@ -615,28 +607,37 @@ int kvm_set_dr(struct kvm_vcpu *vcpu, int dr, unsigned long val)
 
 	return 0;
 }
+
+int kvm_set_dr(struct kvm_vcpu *vcpu, int dr, unsigned long val)
+{
+	int res;
+
+	res = __kvm_set_dr(vcpu, dr, val);
+	if (res > 0)
+		kvm_queue_exception(vcpu, UD_VECTOR);
+	else if (res < 0)
+		kvm_inject_gp(vcpu, 0);
+
+	return res;
+}
 EXPORT_SYMBOL_GPL(kvm_set_dr);
 
-int kvm_get_dr(struct kvm_vcpu *vcpu, int dr, unsigned long *val)
+static int _kvm_get_dr(struct kvm_vcpu *vcpu, int dr, unsigned long *val)
 {
 	switch (dr) {
 	case 0 ... 3:
 		*val = vcpu->arch.db[dr];
 		break;
 	case 4:
-		if (kvm_read_cr4_bits(vcpu, X86_CR4_DE)) {
-			kvm_queue_exception(vcpu, UD_VECTOR);
+		if (kvm_read_cr4_bits(vcpu, X86_CR4_DE))
 			return 1;
-		}
 		/* fall through */
 	case 6:
 		*val = vcpu->arch.dr6;
 		break;
 	case 5:
-		if (kvm_read_cr4_bits(vcpu, X86_CR4_DE)) {
-			kvm_queue_exception(vcpu, UD_VECTOR);
+		if (kvm_read_cr4_bits(vcpu, X86_CR4_DE))
 			return 1;
-		}
 		/* fall through */
 	default: /* 7 */
 		*val = vcpu->arch.dr7;
@@ -645,6 +646,15 @@ int kvm_get_dr(struct kvm_vcpu *vcpu, int dr, unsigned long *val)
 
 	return 0;
 }
+
+int kvm_get_dr(struct kvm_vcpu *vcpu, int dr, unsigned long *val)
+{
+	if (_kvm_get_dr(vcpu, dr, val)) {
+		kvm_queue_exception(vcpu, UD_VECTOR);
+		return 1;
+	}
+	return 0;
+}
 EXPORT_SYMBOL_GPL(kvm_get_dr);
 
 static inline u32 bit(int bitno)
@@ -3619,12 +3629,13 @@ int emulate_clts(struct kvm_vcpu *vcpu)
 
 int emulator_get_dr(int dr, unsigned long *dest, struct kvm_vcpu *vcpu)
 {
-	return kvm_get_dr(vcpu, dr, dest);
+	return _kvm_get_dr(vcpu, dr, dest);
 }
 
 int emulator_set_dr(int dr, unsigned long value, struct kvm_vcpu *vcpu)
 {
-	return kvm_set_dr(vcpu, dr, value);
+
+	return __kvm_set_dr(vcpu, dr, value);
 }
 
 void kvm_report_emulation_failure(struct kvm_vcpu *vcpu, const char *context)