[PATCH v9 75/84] KVM: introspection: add KVMI_VCPU_CONTROL_MSR and KVMI_EVENT_MSR

["Adalbert Lazăr" <alazar@bitdefender.com>]

From: Mihai Donțu <mdontu@bitdefender.com>

This command is used to enable/disable introspection for a specific
MSR. The KVMI_EVENT_MSR event is sent when the tracked MSR is going to
be changed. The introspection tool can respond by allowing the guest to
continue with normal execution or by discarding the change.

This is meant to prevent malicious changes to MSRs
such as MSR_IA32_SYSENTER_EIP.

Signed-off-by: Mihai Donțu <mdontu@bitdefender.com>
Co-developed-by: Nicușor Cîțu <ncitu@bitdefender.com>
Signed-off-by: Nicușor Cîțu <ncitu@bitdefender.com>
Co-developed-by: Adalbert Lazăr <alazar@bitdefender.com>
Signed-off-by: Adalbert Lazăr <alazar@bitdefender.com>
---
 Documentation/virt/kvm/kvmi.rst               |  75 +++++++++
 arch/x86/include/asm/kvmi_host.h              |  12 ++
 arch/x86/include/uapi/asm/kvmi.h              |  18 ++
 arch/x86/kvm/kvmi.c                           | 159 ++++++++++++++++++
 arch/x86/kvm/x86.c                            |   3 +
 include/uapi/linux/kvmi.h                     |   2 +
 .../testing/selftests/kvm/x86_64/kvmi_test.c  | 119 +++++++++++++
 virt/kvm/introspection/kvmi.c                 |   1 +
 virt/kvm/introspection/kvmi_int.h             |   2 +
 virt/kvm/introspection/kvmi_msg.c             |  12 ++
 10 files changed, 403 insertions(+)

diff --git a/Documentation/virt/kvm/kvmi.rst b/Documentation/virt/kvm/kvmi.rst
index 0294c141eb0a..536d6ecec026 100644
--- a/Documentation/virt/kvm/kvmi.rst
+++ b/Documentation/virt/kvm/kvmi.rst
@@ -553,6 +553,7 @@ the following events::
 	KVMI_EVENT_CR
 	KVMI_EVENT_DESCRIPTOR
 	KVMI_EVENT_HYPERCALL
+	KVMI_EVENT_MSR
 	KVMI_EVENT_XSETBV
 
 When an event is enabled, the introspection tool is notified and
@@ -937,6 +938,45 @@ Returns the guest memory type for a specific physical address.
 * -KVM_EINVAL - the padding is not zero
 * -KVM_EAGAIN - the selected vCPU can't be introspected yet
 
+22. KVMI_VCPU_CONTROL_MSR
+-------------------------
+
+:Architectures: x86
+:Versions: >= 1
+:Parameters:
+
+::
+
+	struct kvmi_vcpu_hdr;
+	struct kvmi_vcpu_control_msr {
+		__u8 enable;
+		__u8 padding1;
+		__u16 padding2;
+		__u32 msr;
+	};
+
+:Returns:
+
+::
+
+	struct kvmi_error_code
+
+Enables/disables introspection for a specific MSR and must be used
+in addition to *KVMI_VCPU_CONTROL_EVENTS* with the *KVMI_EVENT_MSR* ID set.
+
+Currently, only MSRs within the following two ranges are supported. Trying
+to control events for any other register will fail with -KVM_EINVAL::
+
+	0          ... 0x00001fff
+	0xc0000000 ... 0xc0001fff
+
+:Errors:
+
+* -KVM_EINVAL - the selected vCPU is invalid
+* -KVM_EINVAL - the specified MSR is invalid
+* -KVM_EINVAL - the padding is not zero
+* -KVM_EAGAIN - the selected vCPU can't be introspected yet
+
 Events
 ======
 
@@ -1252,3 +1292,38 @@ introspection has been enabled for this event (see **KVMI_VCPU_CONTROL_EVENTS**)
 	KVMI_DESC_TR
 
 ``write`` is 1 if the descriptor was written, 0 otherwise.
+
+9. KVMI_EVENT_MSR
+-----------------
+
+:Architectures: x86
+:Versions: >= 1
+:Actions: CONTINUE, CRASH
+:Parameters:
+
+::
+
+	struct kvmi_event;
+	struct kvmi_event_msr {
+		__u32 msr;
+		__u32 padding;
+		__u64 old_value;
+		__u64 new_value;
+	};
+
+:Returns:
+
+::
+
+	struct kvmi_vcpu_hdr;
+	struct kvmi_event_reply;
+	struct kvmi_event_msr_reply {
+		__u64 new_val;
+	};
+
+This event is sent when a model specific register is going to be changed
+and the introspection has been enabled for this event and for this specific
+register (see **KVMI_VCPU_CONTROL_EVENTS**).
+
+``kvmi_event``, the MSR number, the old value and the new value are
+sent to the introspection tool. The *CONTINUE* action will set the ``new_val``.
diff --git a/arch/x86/include/asm/kvmi_host.h b/arch/x86/include/asm/kvmi_host.h
index 0ed1879fd250..5f2967d86b72 100644
--- a/arch/x86/include/asm/kvmi_host.h
+++ b/arch/x86/include/asm/kvmi_host.h
@@ -4,7 +4,10 @@
 
 #include <asm/kvmi.h>
 
+struct msr_data;
+
 #define KVMI_NUM_CR 5
+#define KVMI_NUM_MSR 0x2000
 
 struct kvmi_monitor_interception {
 	bool kvmi_intercepted;
@@ -18,6 +21,12 @@ struct kvmi_interception {
 	struct kvmi_monitor_interception breakpoint;
 	struct kvmi_monitor_interception cr3w;
 	struct kvmi_monitor_interception descriptor;
+	struct {
+		struct {
+			DECLARE_BITMAP(low, KVMI_NUM_MSR);
+			DECLARE_BITMAP(high, KVMI_NUM_MSR);
+		} kvmi_mask;
+	} msrw;
 };
 
 struct kvm_vcpu_arch_introspection {
@@ -38,6 +47,7 @@ void kvmi_xsetbv_event(struct kvm_vcpu *vcpu, u8 xcr,
 		       u64 old_value, u64 new_value);
 bool kvmi_monitor_desc_intercept(struct kvm_vcpu *vcpu, bool enable);
 bool kvmi_descriptor_event(struct kvm_vcpu *vcpu, u8 descriptor, bool write);
+bool kvmi_msr_event(struct kvm_vcpu *vcpu, struct msr_data *msr);
 
 #else /* CONFIG_KVM_INTROSPECTION */
 
@@ -56,6 +66,8 @@ static inline bool kvmi_monitor_desc_intercept(struct kvm_vcpu *vcpu,
 					       bool enable) { return false; }
 static inline bool kvmi_descriptor_event(struct kvm_vcpu *vcpu, u8 descriptor,
 					 bool write) { return true; }
+static inline bool kvmi_msr_event(struct kvm_vcpu *vcpu, struct msr_data *msr)
+				{ return true; }
 
 #endif /* CONFIG_KVM_INTROSPECTION */
 
diff --git a/arch/x86/include/uapi/asm/kvmi.h b/arch/x86/include/uapi/asm/kvmi.h
index b6ff39ba0ab3..1bb13da61dbf 100644
--- a/arch/x86/include/uapi/asm/kvmi.h
+++ b/arch/x86/include/uapi/asm/kvmi.h
@@ -127,4 +127,22 @@ struct kvmi_event_descriptor {
 	__u8 padding[6];
 };
 
+struct kvmi_vcpu_control_msr {
+	__u8 enable;
+	__u8 padding1;
+	__u16 padding2;
+	__u32 msr;
+};
+
+struct kvmi_event_msr {
+	__u32 msr;
+	__u32 padding;
+	__u64 old_value;
+	__u64 new_value;
+};
+
+struct kvmi_event_msr_reply {
+	__u64 new_val;
+};
+
 #endif /* _UAPI_ASM_X86_KVMI_H */
diff --git a/arch/x86/kvm/kvmi.c b/arch/x86/kvm/kvmi.c
index dfe1b887b4f3..a48e72f520da 100644
--- a/arch/x86/kvm/kvmi.c
+++ b/arch/x86/kvm/kvmi.c
@@ -419,6 +419,76 @@ static void kvmi_arch_disable_desc_intercept(struct kvm_vcpu *vcpu)
 	vcpu->arch.kvmi->descriptor.kvm_intercepted = false;
 }
 
+static bool kvmi_msr_valid(unsigned int msr)
+{
+	return msr <= 0x1fff || (msr >= 0xc0000000 && msr <= 0xc0001fff);
+}
+
+static unsigned long *msr_mask(struct kvm_vcpu *vcpu, unsigned int *msr)
+{
+	switch (*msr) {
+	case 0 ... 0x1fff:
+		return vcpu->arch.kvmi->msrw.kvmi_mask.low;
+	case 0xc0000000 ... 0xc0001fff:
+		*msr &= 0x1fff;
+		return vcpu->arch.kvmi->msrw.kvmi_mask.high;
+	}
+
+	return NULL;
+}
+
+static bool test_msr_mask(struct kvm_vcpu *vcpu, unsigned int msr)
+{
+	unsigned long *mask = msr_mask(vcpu, &msr);
+
+	if (!mask)
+		return false;
+
+	return !!test_bit(msr, mask);
+}
+
+static bool msr_control(struct kvm_vcpu *vcpu, unsigned int msr, bool enable)
+{
+	unsigned long *mask = msr_mask(vcpu, &msr);
+
+	if (!mask)
+		return false;
+
+	if (enable)
+		set_bit(msr, mask);
+	else
+		clear_bit(msr, mask);
+
+	return true;
+}
+
+static unsigned int msr_mask_to_base(struct kvm_vcpu *vcpu, unsigned long *mask)
+{
+	if (mask == vcpu->arch.kvmi->msrw.kvmi_mask.high)
+		return 0xc0000000;
+
+	return 0;
+}
+
+static void kvmi_arch_disable_msr_intercept(struct kvm_vcpu *vcpu,
+					    unsigned long *mask)
+{
+	unsigned int msr_base = msr_mask_to_base(vcpu, mask);
+	int offset = -1;
+
+	for (;;) {
+		offset = find_next_bit(mask, KVMI_NUM_MSR, offset + 1);
+
+		if (offset >= KVMI_NUM_MSR)
+			break;
+
+		kvm_x86_ops.control_msr_intercept(vcpu, msr_base + offset,
+						   MSR_TYPE_W, false);
+	}
+
+	bitmap_zero(mask, KVMI_NUM_MSR);
+}
+
 int kvmi_arch_cmd_control_intercept(struct kvm_vcpu *vcpu,
 				    unsigned int event_id, bool enable)
 {
@@ -460,9 +530,13 @@ void kvmi_arch_breakpoint_event(struct kvm_vcpu *vcpu, u64 gva, u8 insn_len)
 
 static void kvmi_arch_restore_interception(struct kvm_vcpu *vcpu)
 {
+	struct kvmi_interception *arch_vcpui = vcpu->arch.kvmi;
+
 	kvmi_arch_disable_bp_intercept(vcpu);
 	kvmi_arch_disable_cr3w_intercept(vcpu);
 	kvmi_arch_disable_desc_intercept(vcpu);
+	kvmi_arch_disable_msr_intercept(vcpu, arch_vcpui->msrw.kvmi_mask.low);
+	kvmi_arch_disable_msr_intercept(vcpu, arch_vcpui->msrw.kvmi_mask.high);
 }
 
 bool kvmi_arch_clean_up_interception(struct kvm_vcpu *vcpu)
@@ -911,3 +985,88 @@ bool kvmi_descriptor_event(struct kvm_vcpu *vcpu, u8 descriptor, bool write)
 	return ret;
 }
 EXPORT_SYMBOL(kvmi_descriptor_event);
+
+int kvmi_arch_cmd_vcpu_control_msr(struct kvm_vcpu *vcpu,
+				   const struct kvmi_vcpu_control_msr *req)
+{
+	if (req->padding1 || req->padding2 || req->enable > 1)
+		return -KVM_EINVAL;
+
+	if (!kvmi_msr_valid(req->msr))
+		return -KVM_EINVAL;
+
+	kvm_x86_ops.control_msr_intercept(vcpu, req->msr, MSR_TYPE_W,
+					  req->enable == 1);
+	msr_control(vcpu, req->msr, req->enable);
+
+	return 0;
+}
+
+static u32 kvmi_send_msr(struct kvm_vcpu *vcpu, u32 msr, u64 old_value,
+			 u64 new_value, u64 *ret_value)
+{
+	struct kvmi_event_msr e;
+	struct kvmi_event_msr_reply r;
+	int err, action;
+
+	memset(&e, 0, sizeof(e));
+	e.msr = msr;
+	e.old_value = old_value;
+	e.new_value = new_value;
+
+	err = kvmi_send_event(vcpu, KVMI_EVENT_MSR, &e, sizeof(e),
+			      &r, sizeof(r), &action);
+	if (err)
+		return KVMI_EVENT_ACTION_CONTINUE;
+
+	*ret_value = r.new_val;
+	return action;
+}
+
+static bool __kvmi_msr_event(struct kvm_vcpu *vcpu, struct msr_data *msr)
+{
+	struct msr_data old_msr = {
+		.host_initiated = true,
+		.index = msr->index,
+	};
+	bool ret = false;
+	u64 ret_value = msr->data;
+	u32 action;
+
+	if (!test_msr_mask(vcpu, msr->index))
+		return true;
+	if (kvm_x86_ops.get_msr(vcpu, &old_msr))
+		return true;
+	if (old_msr.data == msr->data)
+		return true;
+
+	action = kvmi_send_msr(vcpu, msr->index, old_msr.data, msr->data,
+			       &ret_value);
+	switch (action) {
+	case KVMI_EVENT_ACTION_CONTINUE:
+		msr->data = ret_value;
+		ret = true;
+		break;
+	default:
+		kvmi_handle_common_event_actions(vcpu->kvm, action);
+	}
+
+	return ret;
+}
+
+bool kvmi_msr_event(struct kvm_vcpu *vcpu, struct msr_data *msr)
+{
+	struct kvm_introspection *kvmi;
+	bool ret = true;
+
+	kvmi = kvmi_get(vcpu->kvm);
+	if (!kvmi)
+		return true;
+
+	if (is_event_enabled(vcpu, KVMI_EVENT_MSR))
+		ret = __kvmi_msr_event(vcpu, msr);
+
+	kvmi_put(vcpu->kvm);
+
+	return ret;
+}
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index c3557a11817f..0add0b0b8f2d 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1530,6 +1530,9 @@ static int __kvm_set_msr(struct kvm_vcpu *vcpu, u32 index, u64 data,
 	msr.index = index;
 	msr.host_initiated = host_initiated;
 
+	if (!host_initiated && !kvmi_msr_event(vcpu, &msr))
+		return 1;
+
 	return kvm_x86_ops.set_msr(vcpu, &msr);
 }
 
diff --git a/include/uapi/linux/kvmi.h b/include/uapi/linux/kvmi.h
index f2e802d2b712..2872f90ff092 100644
--- a/include/uapi/linux/kvmi.h
+++ b/include/uapi/linux/kvmi.h
@@ -43,6 +43,7 @@ enum {
 	KVMI_VCPU_GET_XSAVE     = 19,
 	KVMI_VCPU_SET_XSAVE     = 20,
 	KVMI_VCPU_GET_MTRR_TYPE = 21,
+	KVMI_VCPU_CONTROL_MSR   = 22,
 
 	KVMI_NUM_MESSAGES
 };
@@ -56,6 +57,7 @@ enum {
 	KVMI_EVENT_TRAP       = 5,
 	KVMI_EVENT_XSETBV     = 6,
 	KVMI_EVENT_DESCRIPTOR = 7,
+	KVMI_EVENT_MSR        = 8,
 
 	KVMI_NUM_EVENTS
 };
diff --git a/tools/testing/selftests/kvm/x86_64/kvmi_test.c b/tools/testing/selftests/kvm/x86_64/kvmi_test.c
index 0087b91574f0..0ddc0029e3e5 100644
--- a/tools/testing/selftests/kvm/x86_64/kvmi_test.c
+++ b/tools/testing/selftests/kvm/x86_64/kvmi_test.c
@@ -57,6 +57,7 @@ enum {
 	GUEST_TEST_CR,
 	GUEST_TEST_DESCRIPTOR,
 	GUEST_TEST_HYPERCALL,
+	GUEST_TEST_MSR,
 	GUEST_TEST_XSETBV,
 };
 
@@ -101,6 +102,15 @@ static void guest_hypercall_test(void)
 	asm volatile(".byte 0x0f,0x01,0xc1");
 }
 
+static void guest_msr_test(void)
+{
+	uint64_t msr;
+
+	msr = rdmsr(MSR_MISC_FEATURES_ENABLES);
+	msr |= 1; /* MSR_MISC_FEATURES_ENABLES_CPUID_FAULT */
+	wrmsr(MSR_MISC_FEATURES_ENABLES, msr);
+}
+
 /* from fpu/internal.h */
 static u64 xgetbv(u32 index)
 {
@@ -158,6 +168,9 @@ static void guest_code(void)
 		case GUEST_TEST_HYPERCALL:
 			guest_hypercall_test();
 			break;
+		case GUEST_TEST_MSR:
+			guest_msr_test();
+			break;
 		case GUEST_TEST_XSETBV:
 			guest_xsetbv_test();
 			break;
@@ -1691,6 +1704,111 @@ static void test_event_descriptor(struct kvm_vm *vm)
 	disable_vcpu_event(vm, event_id);
 }
 
+static void cmd_control_msr(struct kvm_vm *vm, __u32 msr, __u8 enable,
+			    __u8 padding, int expected_err)
+{
+	struct {
+		struct kvmi_msg_hdr hdr;
+		struct kvmi_vcpu_hdr vcpu_hdr;
+		struct kvmi_vcpu_control_msr cmd;
+	} req = {};
+	int r;
+
+	req.cmd.msr = msr;
+	req.cmd.enable = enable;
+	req.cmd.padding1 = padding;
+	req.cmd.padding2 = padding;
+
+	r = do_vcpu0_command(vm, KVMI_VCPU_CONTROL_MSR, &req.hdr, sizeof(req),
+			     NULL, 0);
+	TEST_ASSERT(r == expected_err,
+		"KVMI_VCPU_CONTROL_MSR failed, error %d(%s), expected error %d\n",
+		-r, kvm_strerror(-r), expected_err);
+}
+
+static void enable_msr_events(struct kvm_vm *vm, __u32 msr)
+{
+	enable_vcpu_event(vm, KVMI_EVENT_MSR);
+	cmd_control_msr(vm, msr, 1, 0, 0);
+}
+
+static void disable_msr_events(struct kvm_vm *vm, __u32 msr)
+{
+	cmd_control_msr(vm, msr, 0, 0, 0);
+	disable_vcpu_event(vm, KVMI_EVENT_MSR);
+}
+
+static void handle_msr_event(struct kvm_vm *vm, __u16 event_id, __u32 msr,
+			     __u64 *old_value)
+{
+	struct kvmi_msg_hdr hdr;
+	struct {
+		struct kvmi_event common;
+		struct kvmi_event_msr msr;
+	} ev;
+	struct {
+		struct vcpu_reply common;
+		struct kvmi_event_msr_reply msr;
+	} rpl = {};
+
+	receive_event(&hdr, &ev.common, sizeof(ev), event_id);
+
+	pr_info("MSR 0x%x, old 0x%llx, new 0x%llx\n",
+		ev.msr.msr, ev.msr.old_value, ev.msr.new_value);
+
+	TEST_ASSERT(ev.msr.msr == msr,
+		"Unexpected MSR event, received MSR 0x%x, expected MSR 0x%x",
+		ev.msr.msr, msr);
+
+	*old_value = rpl.msr.new_val = ev.msr.old_value;
+
+	reply_to_event(&hdr, &ev.common, KVMI_EVENT_ACTION_CONTINUE,
+			&rpl.common, sizeof(rpl));
+}
+
+static void test_invalid_control_msr(struct kvm_vm *vm, __u32 msr)
+{
+	__u8 enable = 1, enable_inval = 2;
+	__u8 no_padding = 0, padding = 1;
+	int expected_err = -KVM_EINVAL;
+	__u32 msr_inval = -1;
+
+	cmd_control_msr(vm, msr, enable_inval, no_padding, expected_err);
+	cmd_control_msr(vm, msr, enable, padding, expected_err);
+	cmd_control_msr(vm, msr_inval, enable, no_padding, expected_err);
+}
+
+static void test_cmd_vcpu_control_msr(struct kvm_vm *vm)
+{
+	struct vcpu_worker_data data = {
+		.vm = vm,
+		.vcpu_id = VCPU_ID,
+		.test_id = GUEST_TEST_MSR,
+	};
+	__u16 event_id = KVMI_EVENT_MSR;
+	__u32 msr = MSR_MISC_FEATURES_ENABLES;
+	pthread_t vcpu_thread;
+	uint64_t msr_data;
+	__u64 old_value;
+
+	enable_msr_events(vm, msr);
+
+	vcpu_thread = start_vcpu_worker(&data);
+
+	handle_msr_event(vm, event_id, msr, &old_value);
+
+	stop_vcpu_worker(vcpu_thread, &data);
+
+	disable_msr_events(vm, msr);
+
+	msr_data = vcpu_get_msr(vm, VCPU_ID, msr);
+	TEST_ASSERT(msr_data == old_value,
+		"Failed to block MSR 0x%x update, value 0x%lx, expected 0x%llx",
+		msr, msr_data, old_value);
+
+	test_invalid_control_msr(vm, msr);
+}
+
 static void test_introspection(struct kvm_vm *vm)
 {
 	srandom(time(0));
@@ -1722,6 +1840,7 @@ static void test_introspection(struct kvm_vm *vm)
 	test_cmd_vcpu_xsave(vm);
 	test_cmd_vcpu_get_mtrr_type(vm);
 	test_event_descriptor(vm);
+	test_cmd_vcpu_control_msr(vm);
 
 	unhook_introspection(vm);
 }
diff --git a/virt/kvm/introspection/kvmi.c b/virt/kvm/introspection/kvmi.c
index a1bc9570ac1c..aa8a0708cc1c 100644
--- a/virt/kvm/introspection/kvmi.c
+++ b/virt/kvm/introspection/kvmi.c
@@ -101,6 +101,7 @@ static void setup_known_events(void)
 	set_bit(KVMI_EVENT_CR, Kvmi_known_vcpu_events);
 	set_bit(KVMI_EVENT_DESCRIPTOR, Kvmi_known_vcpu_events);
 	set_bit(KVMI_EVENT_HYPERCALL, Kvmi_known_vcpu_events);
+	set_bit(KVMI_EVENT_MSR, Kvmi_known_vcpu_events);
 	set_bit(KVMI_EVENT_PAUSE_VCPU, Kvmi_known_vcpu_events);
 	set_bit(KVMI_EVENT_TRAP, Kvmi_known_vcpu_events);
 	set_bit(KVMI_EVENT_XSETBV, Kvmi_known_vcpu_events);
diff --git a/virt/kvm/introspection/kvmi_int.h b/virt/kvm/introspection/kvmi_int.h
index a9664d255d6d..8f8557bd8ab0 100644
--- a/virt/kvm/introspection/kvmi_int.h
+++ b/virt/kvm/introspection/kvmi_int.h
@@ -115,5 +115,7 @@ int kvmi_arch_cmd_vcpu_set_xsave(struct kvm_vcpu *vcpu,
 				 const struct kvmi_vcpu_set_xsave *req,
 				 size_t req_size);
 int kvmi_arch_cmd_vcpu_get_mtrr_type(struct kvm_vcpu *vcpu, u64 gpa, u8 *type);
+int kvmi_arch_cmd_vcpu_control_msr(struct kvm_vcpu *vcpu,
+				   const struct kvmi_vcpu_control_msr *req);
 
 #endif
diff --git a/virt/kvm/introspection/kvmi_msg.c b/virt/kvm/introspection/kvmi_msg.c
index 36819b54b3a0..d9cbbefb9993 100644
--- a/virt/kvm/introspection/kvmi_msg.c
+++ b/virt/kvm/introspection/kvmi_msg.c
@@ -584,6 +584,17 @@ static int handle_vcpu_get_mtrr_type(const struct kvmi_vcpu_msg_job *job,
 	return kvmi_msg_vcpu_reply(job, msg, ec, &rpl, sizeof(rpl));
 }
 
+static int handle_vcpu_control_msr(const struct kvmi_vcpu_msg_job *job,
+				   const struct kvmi_msg_hdr *msg,
+				   const void *req)
+{
+	int ec;
+
+	ec = kvmi_arch_cmd_vcpu_control_msr(job->vcpu, req);
+
+	return kvmi_msg_vcpu_reply(job, msg, ec, NULL, 0);
+}
+
 /*
  * These functions are executed from the vCPU thread. The receiving thread
  * passes the messages using a newly allocated 'struct kvmi_vcpu_msg_job'
@@ -595,6 +606,7 @@ static int(*const msg_vcpu[])(const struct kvmi_vcpu_msg_job *,
 	[KVMI_EVENT]                 = handle_vcpu_event_reply,
 	[KVMI_VCPU_CONTROL_CR]       = handle_vcpu_control_cr,
 	[KVMI_VCPU_CONTROL_EVENTS]   = handle_vcpu_control_events,
+	[KVMI_VCPU_CONTROL_MSR]      = handle_vcpu_control_msr,
 	[KVMI_VCPU_GET_CPUID]        = handle_vcpu_get_cpuid,
 	[KVMI_VCPU_GET_INFO]         = handle_vcpu_get_info,
 	[KVMI_VCPU_GET_MTRR_TYPE]    = handle_vcpu_get_mtrr_type,