[RFC PATCH v7 74/78] KVM: introspection: add KVMI_VCPU_CONTROL_SINGLESTEP

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

From: Nicușor Cîțu <ncitu@bitdefender.com>

This command is extremely useful for debuggers.

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               | 31 ++++++
 arch/x86/kvm/kvmi.c                           | 18 ++++
 arch/x86/kvm/x86.c                            |  7 ++
 include/linux/kvmi_host.h                     |  7 ++
 include/uapi/linux/kvmi.h                     |  7 ++
 .../testing/selftests/kvm/x86_64/kvmi_test.c  | 21 +++++
 virt/kvm/introspection/kvmi.c                 | 23 +++++
 virt/kvm/introspection/kvmi_int.h             |  3 +
 virt/kvm/introspection/kvmi_msg.c             | 94 ++++++++++++-------
 9 files changed, 179 insertions(+), 32 deletions(-)

diff --git a/Documentation/virt/kvm/kvmi.rst b/Documentation/virt/kvm/kvmi.rst
index 454d7ae75ae6..ffa183745722 100644
--- a/Documentation/virt/kvm/kvmi.rst
+++ b/Documentation/virt/kvm/kvmi.rst
@@ -930,6 +930,37 @@ In order to 'forget' an address, all the access bits ('rwx') must be set.
 * -KVM_EINVAL - the message size is invalid
 * -KVM_ENOMEM - not enough memory to add the page tracking structures
 
+20. KVMI_VCPU_CONTROL_SINGLESTEP
+--------------------------------
+
+:Architectures: x86 (vmx)
+:Versions: >= 1
+:Parameters:
+
+::
+
+	struct kvmi_vcpu_control_singlestep {
+		__u8 enable;
+		__u8 padding[7];
+	};
+
+:Returns:
+
+::
+
+	struct kvmi_error_code
+
+Enables/disables singlestep.
+
+The introspection tool can use *KVMI_GET_VERSION*, to check
+if the hardware supports singlestep (see **KVMI_GET_VERSION**).
+
+:Errors:
+
+* -KVM_EOPNOTSUPP - the hardware doesn't support it
+* -KVM_EINVAL - padding is not zero
+* -KVM_EAGAIN - the selected vCPU can't be introspected yet
+
 Events
 ======
 
diff --git a/arch/x86/kvm/kvmi.c b/arch/x86/kvm/kvmi.c
index 5cf266d13375..feebb0327e27 100644
--- a/arch/x86/kvm/kvmi.c
+++ b/arch/x86/kvm/kvmi.c
@@ -1111,3 +1111,21 @@ bool kvmi_arch_pf_of_interest(struct kvm_vcpu *vcpu)
 	      !kvm_x86_ops->gpt_translation_fault(vcpu);
 }
 
+bool kvmi_arch_start_singlestep(struct kvm_vcpu *vcpu)
+{
+	if (!kvm_x86_ops->control_singlestep)
+		return false;
+
+	kvm_x86_ops->control_singlestep(vcpu, true);
+	return true;
+}
+
+bool kvmi_arch_stop_singlestep(struct kvm_vcpu *vcpu)
+{
+	if (!kvm_x86_ops->control_singlestep)
+		return false;
+
+	kvm_x86_ops->control_singlestep(vcpu, false);
+	return true;
+}
+
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 5d6ac6c99246..b87ff31ce486 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -7625,6 +7625,13 @@ static int inject_pending_event(struct kvm_vcpu *vcpu, bool req_int_win)
 {
 	int r;
 
+	if (kvmi_vcpu_running_singlestep(vcpu))
+		/*
+		 * We cannot inject events during single-stepping.
+		 * Try again later.
+		 */
+		return -1;
+
 	/* try to reinject previous events if any */
 
 	if (vcpu->arch.exception.injected)
diff --git a/include/linux/kvmi_host.h b/include/linux/kvmi_host.h
index a9f572df1809..7c84ca681411 100644
--- a/include/linux/kvmi_host.h
+++ b/include/linux/kvmi_host.h
@@ -50,6 +50,10 @@ struct kvm_vcpu_introspection {
 		bool pending;
 		bool send_event;
 	} exception;
+
+	struct {
+		bool loop;
+	} singlestep;
 };
 
 struct kvm_introspection {
@@ -90,6 +94,7 @@ void kvmi_handle_requests(struct kvm_vcpu *vcpu);
 bool kvmi_hypercall_event(struct kvm_vcpu *vcpu);
 bool kvmi_breakpoint_event(struct kvm_vcpu *vcpu, u64 gva, u8 insn_len);
 bool kvmi_enter_guest(struct kvm_vcpu *vcpu);
+bool kvmi_vcpu_running_singlestep(struct kvm_vcpu *vcpu);
 
 #else
 
@@ -106,6 +111,8 @@ static inline bool kvmi_breakpoint_event(struct kvm_vcpu *vcpu, u64 gva,
 			{ return true; }
 static inline bool kvmi_enter_guest(struct kvm_vcpu *vcpu)
 			{ return true; }
+static inline bool kvmi_vcpu_running_singlestep(struct kvm_vcpu *vcpu)
+			{ return false; }
 
 #endif /* CONFIG_KVM_INTROSPECTION */
 
diff --git a/include/uapi/linux/kvmi.h b/include/uapi/linux/kvmi.h
index 7cd41a815967..c6c5019ccf85 100644
--- a/include/uapi/linux/kvmi.h
+++ b/include/uapi/linux/kvmi.h
@@ -43,6 +43,8 @@ enum {
 
 	KVMI_VM_SET_PAGE_ACCESS = 21,
 
+	KVMI_VCPU_CONTROL_SINGLESTEP = 22,
+
 	KVMI_NUM_MESSAGES
 };
 
@@ -168,6 +170,11 @@ struct kvmi_vm_set_page_access {
 	struct kvmi_page_access_entry entries[0];
 };
 
+struct kvmi_vcpu_control_singlestep {
+	__u8 enable;
+	__u8 padding[7];
+};
+
 struct kvmi_event {
 	__u16 size;
 	__u16 vcpu;
diff --git a/tools/testing/selftests/kvm/x86_64/kvmi_test.c b/tools/testing/selftests/kvm/x86_64/kvmi_test.c
index a27588c27eb8..090cb7acd2ed 100644
--- a/tools/testing/selftests/kvm/x86_64/kvmi_test.c
+++ b/tools/testing/selftests/kvm/x86_64/kvmi_test.c
@@ -1681,6 +1681,26 @@ static void test_event_pf(struct kvm_vm *vm)
 	test_pf(vm, cbk_test_event_pf);
 }
 
+static void test_cmd_vcpu_control_singlestep(struct kvm_vm *vm)
+{
+	struct {
+		struct kvmi_msg_hdr hdr;
+		struct kvmi_vcpu_hdr vcpu_hdr;
+		struct kvmi_vcpu_control_singlestep cmd;
+	} req = {};
+
+	if (!features.singlestep)
+		return;
+
+	req.cmd.enable = true;
+	test_vcpu0_command(vm, KVMI_VCPU_CONTROL_SINGLESTEP,
+			   &req.hdr, sizeof(req), NULL, 0);
+
+	req.cmd.enable = false;
+	test_vcpu0_command(vm, KVMI_VCPU_CONTROL_SINGLESTEP,
+			   &req.hdr, sizeof(req), NULL, 0);
+}
+
 static void test_introspection(struct kvm_vm *vm)
 {
 	setup_socket();
@@ -1712,6 +1732,7 @@ static void test_introspection(struct kvm_vm *vm)
 	test_cmd_vcpu_control_msr(vm);
 	test_cmd_vm_set_page_access(vm);
 	test_event_pf(vm);
+	test_cmd_vcpu_control_singlestep(vm);
 
 	unhook_introspection(vm);
 }
diff --git a/virt/kvm/introspection/kvmi.c b/virt/kvm/introspection/kvmi.c
index 10d59061fa82..b798eeab6618 100644
--- a/virt/kvm/introspection/kvmi.c
+++ b/virt/kvm/introspection/kvmi.c
@@ -361,6 +361,9 @@ static void kvmi_job_release_vcpu(struct kvm_vcpu *vcpu, void *ctx)
 
 	atomic_set(&vcpui->pause_requests, 0);
 	vcpui->waiting_for_reply = false;
+
+	if (vcpui->singlestep.loop)
+		kvmi_arch_stop_singlestep(vcpu);
 }
 
 static void kvmi_release_vcpus(struct kvm *kvm)
@@ -1003,6 +1006,9 @@ bool kvmi_enter_guest(struct kvm_vcpu *vcpu)
 	if (!kvmi)
 		return true;
 
+	if (VCPUI(vcpu)->singlestep.loop)
+		kvmi_arch_start_singlestep(vcpu);
+
 	if (kvmi_inject_pending_exception(vcpu))
 		r = false;
 
@@ -1296,3 +1302,20 @@ static void kvmi_track_flush_slot(struct kvm *kvm, struct kvm_memory_slot *slot,
 
 	kvmi_put(kvm);
 }
+
+bool kvmi_vcpu_running_singlestep(struct kvm_vcpu *vcpu)
+{
+	struct kvm_introspection *kvmi;
+	bool ret;
+
+	kvmi = kvmi_get(vcpu->kvm);
+	if (!kvmi)
+		return false;
+
+	ret = VCPUI(vcpu)->singlestep.loop;
+
+	kvmi_put(vcpu->kvm);
+
+	return ret;
+}
+EXPORT_SYMBOL(kvmi_vcpu_running_singlestep);
diff --git a/virt/kvm/introspection/kvmi_int.h b/virt/kvm/introspection/kvmi_int.h
index 06b924277f37..64425ff16c7d 100644
--- a/virt/kvm/introspection/kvmi_int.h
+++ b/virt/kvm/introspection/kvmi_int.h
@@ -50,6 +50,7 @@
 			| BIT(KVMI_VCPU_CONTROL_CR) \
 			| BIT(KVMI_VCPU_CONTROL_EVENTS) \
 			| BIT(KVMI_VCPU_CONTROL_MSR) \
+			| BIT(KVMI_VCPU_CONTROL_SINGLESTEP) \
 			| BIT(KVMI_VCPU_GET_CPUID) \
 			| BIT(KVMI_VCPU_GET_MTRR_TYPE) \
 			| BIT(KVMI_VCPU_GET_REGISTERS) \
@@ -168,5 +169,7 @@ bool kvmi_arch_pf_event(struct kvm_vcpu *vcpu, gpa_t gpa, gva_t gva,
 			u8 access);
 bool kvmi_arch_pf_of_interest(struct kvm_vcpu *vcpu);
 void kvmi_arch_features(struct kvmi_features *feat);
+bool kvmi_arch_start_singlestep(struct kvm_vcpu *vcpu);
+bool kvmi_arch_stop_singlestep(struct kvm_vcpu *vcpu);
 
 #endif
diff --git a/virt/kvm/introspection/kvmi_msg.c b/virt/kvm/introspection/kvmi_msg.c
index 8c7cdbd96faa..4c49033a6407 100644
--- a/virt/kvm/introspection/kvmi_msg.c
+++ b/virt/kvm/introspection/kvmi_msg.c
@@ -17,27 +17,28 @@ struct kvmi_vcpu_cmd_job {
 };
 
 static const char *const msg_IDs[] = {
-	[KVMI_EVENT_REPLY]           = "KVMI_EVENT_REPLY",
-	[KVMI_GET_VERSION]           = "KVMI_GET_VERSION",
-	[KVMI_VM_CHECK_COMMAND]      = "KVMI_VM_CHECK_COMMAND",
-	[KVMI_VM_CHECK_EVENT]        = "KVMI_VM_CHECK_EVENT",
-	[KVMI_VM_CONTROL_EVENTS]     = "KVMI_VM_CONTROL_EVENTS",
-	[KVMI_VM_GET_INFO]           = "KVMI_VM_GET_INFO",
-	[KVMI_VM_GET_MAX_GFN]        = "KVMI_VM_GET_MAX_GFN",
-	[KVMI_VM_READ_PHYSICAL]      = "KVMI_VM_READ_PHYSICAL",
-	[KVMI_VM_SET_PAGE_ACCESS]    = "KVMI_VM_SET_PAGE_ACCESS",
-	[KVMI_VM_WRITE_PHYSICAL]     = "KVMI_VM_WRITE_PHYSICAL",
-	[KVMI_VCPU_CONTROL_CR]       = "KVMI_VCPU_CONTROL_CR",
-	[KVMI_VCPU_CONTROL_EVENTS]   = "KVMI_VCPU_CONTROL_EVENTS",
-	[KVMI_VCPU_CONTROL_MSR]      = "KVMI_VCPU_CONTROL_MSR",
-	[KVMI_VCPU_GET_CPUID]        = "KVMI_VCPU_GET_CPUID",
-	[KVMI_VCPU_GET_INFO]         = "KVMI_VCPU_GET_INFO",
-	[KVMI_VCPU_GET_MTRR_TYPE]    = "KVMI_VCPU_GET_MTRR_TYPE",
-	[KVMI_VCPU_GET_REGISTERS]    = "KVMI_VCPU_GET_REGISTERS",
-	[KVMI_VCPU_GET_XSAVE]        = "KVMI_VCPU_GET_XSAVE",
-	[KVMI_VCPU_INJECT_EXCEPTION] = "KVMI_VCPU_INJECT_EXCEPTION",
-	[KVMI_VCPU_PAUSE]            = "KVMI_VCPU_PAUSE",
-	[KVMI_VCPU_SET_REGISTERS]    = "KVMI_VCPU_SET_REGISTERS",
+	[KVMI_EVENT_REPLY]             = "KVMI_EVENT_REPLY",
+	[KVMI_GET_VERSION]             = "KVMI_GET_VERSION",
+	[KVMI_VM_CHECK_COMMAND]        = "KVMI_VM_CHECK_COMMAND",
+	[KVMI_VM_CHECK_EVENT]          = "KVMI_VM_CHECK_EVENT",
+	[KVMI_VM_CONTROL_EVENTS]       = "KVMI_VM_CONTROL_EVENTS",
+	[KVMI_VM_GET_INFO]             = "KVMI_VM_GET_INFO",
+	[KVMI_VM_GET_MAX_GFN]          = "KVMI_VM_GET_MAX_GFN",
+	[KVMI_VM_READ_PHYSICAL]        = "KVMI_VM_READ_PHYSICAL",
+	[KVMI_VM_SET_PAGE_ACCESS]      = "KVMI_VM_SET_PAGE_ACCESS",
+	[KVMI_VM_WRITE_PHYSICAL]       = "KVMI_VM_WRITE_PHYSICAL",
+	[KVMI_VCPU_CONTROL_CR]         = "KVMI_VCPU_CONTROL_CR",
+	[KVMI_VCPU_CONTROL_EVENTS]     = "KVMI_VCPU_CONTROL_EVENTS",
+	[KVMI_VCPU_CONTROL_MSR]        = "KVMI_VCPU_CONTROL_MSR",
+	[KVMI_VCPU_CONTROL_SINGLESTEP] = "KVMI_VCPU_CONTROL_SINGLESTEP",
+	[KVMI_VCPU_GET_CPUID]          = "KVMI_VCPU_GET_CPUID",
+	[KVMI_VCPU_GET_INFO]           = "KVMI_VCPU_GET_INFO",
+	[KVMI_VCPU_GET_MTRR_TYPE]      = "KVMI_VCPU_GET_MTRR_TYPE",
+	[KVMI_VCPU_GET_REGISTERS]      = "KVMI_VCPU_GET_REGISTERS",
+	[KVMI_VCPU_GET_XSAVE]          = "KVMI_VCPU_GET_XSAVE",
+	[KVMI_VCPU_INJECT_EXCEPTION]   = "KVMI_VCPU_INJECT_EXCEPTION",
+	[KVMI_VCPU_PAUSE]              = "KVMI_VCPU_PAUSE",
+	[KVMI_VCPU_SET_REGISTERS]      = "KVMI_VCPU_SET_REGISTERS",
 };
 
 static bool is_known_message(u16 id)
@@ -585,6 +586,34 @@ static int handle_vcpu_control_msr(const struct kvmi_vcpu_cmd_job *job,
 	return kvmi_msg_vcpu_reply(job, msg, ec, NULL, 0);
 }
 
+static int handle_vcpu_control_singlestep(const struct kvmi_vcpu_cmd_job *job,
+					  const struct kvmi_msg_hdr *msg,
+					  const void *_req)
+{
+	const struct kvmi_vcpu_control_singlestep *req = _req;
+	struct kvm_vcpu *vcpu = job->vcpu;
+	int ec = -KVM_EINVAL;
+	bool done;
+	int i;
+
+	for (i = 0; i < sizeof(req->padding); i++)
+		if (req->padding[i])
+			goto reply;
+
+	if (req->enable)
+		done = kvmi_arch_start_singlestep(vcpu);
+	else
+		done = kvmi_arch_stop_singlestep(vcpu);
+
+	if (done) {
+		ec = 0;
+		VCPUI(vcpu)->singlestep.loop = !!req->enable;
+	}
+
+reply:
+	return kvmi_msg_vcpu_reply(job, msg, ec, NULL, 0);
+}
+
 /*
  * These commands are executed on the vCPU thread. The receiving thread
  * passes the messages using a newly allocated 'struct kvmi_vcpu_cmd_job'
@@ -593,17 +622,18 @@ static int handle_vcpu_control_msr(const struct kvmi_vcpu_cmd_job *job,
  */
 static int(*const msg_vcpu[])(const struct kvmi_vcpu_cmd_job *,
 			      const struct kvmi_msg_hdr *, const void *) = {
-	[KVMI_EVENT_REPLY]           = handle_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_get_cpuid,
-	[KVMI_VCPU_GET_INFO]         = handle_get_vcpu_info,
-	[KVMI_VCPU_GET_MTRR_TYPE]    = handle_vcpu_get_mtrr_type,
-	[KVMI_VCPU_GET_REGISTERS]    = handle_get_registers,
-	[KVMI_VCPU_GET_XSAVE]        = handle_vcpu_get_xsave,
-	[KVMI_VCPU_INJECT_EXCEPTION] = handle_vcpu_inject_exception,
-	[KVMI_VCPU_SET_REGISTERS]    = handle_set_registers,
+	[KVMI_EVENT_REPLY]             = handle_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_CONTROL_SINGLESTEP] = handle_vcpu_control_singlestep,
+	[KVMI_VCPU_GET_CPUID]          = handle_get_cpuid,
+	[KVMI_VCPU_GET_INFO]           = handle_get_vcpu_info,
+	[KVMI_VCPU_GET_MTRR_TYPE]      = handle_vcpu_get_mtrr_type,
+	[KVMI_VCPU_GET_REGISTERS]      = handle_get_registers,
+	[KVMI_VCPU_GET_XSAVE]          = handle_vcpu_get_xsave,
+	[KVMI_VCPU_INJECT_EXCEPTION]   = handle_vcpu_inject_exception,
+	[KVMI_VCPU_SET_REGISTERS]      = handle_set_registers,
 };
 
 static void kvmi_job_vcpu_cmd(struct kvm_vcpu *vcpu, void *ctx)