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From: Michael Roth <michael.roth@amd.com>
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Subject: [PATCH v11 35/35] KVM: SEV: Provide support for SNP_EXTENDED_GUEST_REQUEST NAE event
Date: Sat, 30 Dec 2023 11:23:51 -0600
Message-ID: <20231230172351.574091-36-michael.roth@amd.com>
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Version 2 of GHCB specification added support for the SNP Extended Guest
Request Message NAE event. This event serves a nearly identical purpose
to the previously-added SNP_GUEST_REQUEST event, but allows for
additional certificate data to be supplied via an additional
guest-supplied buffer to be used mainly for verifying the signature of
an attestation report as returned by firmware.

This certificate data is supplied by userspace, so unlike with
SNP_GUEST_REQUEST events, SNP_EXTENDED_GUEST_REQUEST events are first
forwarded to userspace via a KVM_EXIT_VMGEXIT exit type, and then the
firmware request is made only afterward.

Implement handling for these events.

Since there is a potential for race conditions where the
userspace-supplied certificate data may be out-of-sync relative to the
reported TCB that firmware will use when signing attestation reports,
make use of the transaction/synchronization mechanisms added by the
SNP_SET_CONFIG_{START,END} SEV device ioctls such that the guest will be
told to retry the request when an update to reported TCB or
userspace-supplied certificates may have occurred or is in progress
while an extended guest request is being processed.

Signed-off-by: Michael Roth <michael.roth@amd.com>
---
 Documentation/virt/kvm/api.rst | 26 ++++++++++++
 arch/x86/include/asm/sev.h     |  4 ++
 arch/x86/kvm/svm/sev.c         | 75 ++++++++++++++++++++++++++++++++++
 arch/x86/kvm/svm/svm.h         |  3 ++
 arch/x86/virt/svm/sev.c        | 20 +++++++++
 include/uapi/linux/kvm.h       |  6 +++
 6 files changed, 134 insertions(+)

diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index 2a526b4f8e06..960e2153d468 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -7037,6 +7037,7 @@ values in kvm_run even if the corresponding bit in kvm_dirty_regs is not set.
 		struct kvm_user_vmgexit {
 		#define KVM_USER_VMGEXIT_PSC_MSR	1
 		#define KVM_USER_VMGEXIT_PSC		2
+		#define KVM_USER_VMGEXIT_EXT_GUEST_REQ	3
 			__u32 type; /* KVM_USER_VMGEXIT_* type */
 			union {
 				struct {
@@ -7050,6 +7051,11 @@ values in kvm_run even if the corresponding bit in kvm_dirty_regs is not set.
 					__u64 shared_gpa;
 					__u64 ret;
 				} psc;
+				struct {
+					__u64 data_gpa;
+					__u64 data_npages;
+					__u32 ret;
+				} ext_guest_req;
 			};
 		};
 
@@ -7079,6 +7085,26 @@ private/shared state. Userspace will return a value in 'ret' that is in
 agreement with the GHCB-defined return values that the guest will expect
 in the SW_EXITINFO2 field of the GHCB in response to these requests.
 
+For the KVM_USER_VMGEXIT_EXT_GUEST_REQ type, the ext_guest_req union type
+is used. The kernel will supply in 'data_gpa' the value the guest supplies
+via the RAX field of the GHCB when issued extended guest requests.
+'data_npages' will similarly contain the value the guest supplies in RBX
+denoting the number of shared pages available to write the certificate
+data into.
+
+  - If the supplied number of pages is sufficient, userspace should write
+    the certificate data blob (in the format defined by the GHCB spec) in
+    the address indicated by 'data_gpa' and set 'ret' to 0.
+
+  - If the number of pages supplied is not sufficient, userspace must write
+    the required number of pages in 'data_npages' and then set 'ret' to 1.
+
+  - If userspace is temporarily unable to handle the request, 'ret' should
+    be set to 2 to inform the guest to retry later.
+
+  - If some other error occurred, userspace should set 'ret' to a non-zero
+    value that is distinct from the specific return values mentioned above.
+
 6. Capabilities that can be enabled on vCPUs
 ============================================
 
diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
index 925578ad34e6..25f533827d62 100644
--- a/arch/x86/include/asm/sev.h
+++ b/arch/x86/include/asm/sev.h
@@ -270,6 +270,8 @@ int rmp_make_shared(u64 pfn, enum pg_level level);
 void snp_leak_pages(u64 pfn, unsigned int npages);
 u64 snp_config_transaction_start(void);
 u64 snp_config_transaction_end(void);
+u64 snp_config_transaction_get_id(void);
+bool snp_config_transaction_is_stale(u64 id);
 #else
 static inline bool snp_probe_rmptable_info(void) { return false; }
 static inline int snp_lookup_rmpentry(u64 pfn, bool *assigned, int *level) { return -ENODEV; }
@@ -284,6 +286,8 @@ static inline int rmp_make_shared(u64 pfn, enum pg_level level) { return -ENODEV
 static inline void snp_leak_pages(u64 pfn, unsigned int npages) {}
 static inline u64 snp_config_transaction_start(void) { return 0; }
 static inline u64 snp_config_transaction_end(void) { return 0; }
+static inline u64 snp_config_transaction_get_id(void) { return 0; }
+static inline bool snp_config_transaction_is_stale(u64 id) { return false; }
 #endif
 
 #endif
diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 05051e36926d..dda195999c42 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -3111,6 +3111,7 @@ static int sev_es_validate_vmgexit(struct vcpu_svm *svm)
 	case SVM_VMGEXIT_PSC:
 	case SVM_VMGEXIT_TERM_REQUEST:
 	case SVM_VMGEXIT_GUEST_REQUEST:
+	case SVM_VMGEXIT_EXT_GUEST_REQUEST:
 		break;
 	default:
 		reason = GHCB_ERR_INVALID_EVENT;
@@ -3618,6 +3619,77 @@ static void snp_handle_guest_req(struct vcpu_svm *svm, gpa_t req_gpa, gpa_t resp
 	ghcb_set_sw_exit_info_2(svm->sev_es.ghcb, SNP_GUEST_ERR(vmm_ret, fw_err));
 }
 
+static int snp_complete_ext_guest_req(struct kvm_vcpu *vcpu)
+{
+	struct vcpu_svm *svm = to_svm(vcpu);
+	struct vmcb_control_area *control;
+	struct kvm *kvm = vcpu->kvm;
+	sev_ret_code fw_err = 0;
+	int vmm_ret;
+
+	vmm_ret = vcpu->run->vmgexit.ext_guest_req.ret;
+	if (vmm_ret) {
+		if (vmm_ret == SNP_GUEST_VMM_ERR_INVALID_LEN)
+			vcpu->arch.regs[VCPU_REGS_RBX] =
+				vcpu->run->vmgexit.ext_guest_req.data_npages;
+		goto abort_request;
+	}
+
+	control = &svm->vmcb->control;
+
+	if (!__snp_handle_guest_req(kvm, control->exit_info_1, control->exit_info_2,
+				    &fw_err))
+		vmm_ret = SNP_GUEST_VMM_ERR_GENERIC;
+
+	/*
+	 * Give errors related to stale transactions precedence to provide more
+	 * potential options for servicing firmware while guests are running.
+	 */
+	if (snp_config_transaction_is_stale(svm->snp_transaction_id))
+		vmm_ret = SNP_GUEST_VMM_ERR_BUSY;
+
+abort_request:
+	ghcb_set_sw_exit_info_2(svm->sev_es.ghcb, SNP_GUEST_ERR(vmm_ret, fw_err));
+
+	return 1; /* resume guest */
+}
+
+static int snp_begin_ext_guest_req(struct kvm_vcpu *vcpu)
+{
+	int vmm_ret = SNP_GUEST_VMM_ERR_GENERIC;
+	struct vcpu_svm *svm = to_svm(vcpu);
+	unsigned long data_npages;
+	sev_ret_code fw_err;
+	gpa_t data_gpa;
+
+	if (!sev_snp_guest(vcpu->kvm))
+		goto abort_request;
+
+	data_gpa = vcpu->arch.regs[VCPU_REGS_RAX];
+	data_npages = vcpu->arch.regs[VCPU_REGS_RBX];
+
+	if (!IS_ALIGNED(data_gpa, PAGE_SIZE))
+		goto abort_request;
+
+	svm->snp_transaction_id = snp_config_transaction_get_id();
+	if (snp_config_transaction_is_stale(svm->snp_transaction_id)) {
+		vmm_ret = SNP_GUEST_VMM_ERR_BUSY;
+		goto abort_request;
+	}
+
+	vcpu->run->exit_reason = KVM_EXIT_VMGEXIT;
+	vcpu->run->vmgexit.type = KVM_USER_VMGEXIT_EXT_GUEST_REQ;
+	vcpu->run->vmgexit.ext_guest_req.data_gpa = data_gpa;
+	vcpu->run->vmgexit.ext_guest_req.data_npages = data_npages;
+	vcpu->arch.complete_userspace_io = snp_complete_ext_guest_req;
+
+	return 0; /* forward request to userspace */
+
+abort_request:
+	ghcb_set_sw_exit_info_2(svm->sev_es.ghcb, SNP_GUEST_ERR(vmm_ret, fw_err));
+	return 1; /* resume guest */
+}
+
 static int sev_handle_vmgexit_msr_protocol(struct vcpu_svm *svm)
 {
 	struct vmcb_control_area *control = &svm->vmcb->control;
@@ -3882,6 +3954,9 @@ int sev_handle_vmgexit(struct kvm_vcpu *vcpu)
 		snp_handle_guest_req(svm, control->exit_info_1, control->exit_info_2);
 		ret = 1;
 		break;
+	case SVM_VMGEXIT_EXT_GUEST_REQUEST:
+		ret = snp_begin_ext_guest_req(vcpu);
+		break;
 	case SVM_VMGEXIT_UNSUPPORTED_EVENT:
 		vcpu_unimpl(vcpu,
 			    "vmgexit: unsupported event - exit_info_1=%#llx, exit_info_2=%#llx\n",
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index a56109e100ac..a2ac6dc3a79a 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -307,6 +307,9 @@ struct vcpu_svm {
 
 	/* Guest GIF value, used when vGIF is not enabled */
 	bool guest_gif;
+
+	/* Transaction ID associated with SNP config updates */
+	u64 snp_transaction_id;
 };
 
 struct svm_cpu_data {
diff --git a/arch/x86/virt/svm/sev.c b/arch/x86/virt/svm/sev.c
index fc9e1b7fc187..fee273a84030 100644
--- a/arch/x86/virt/svm/sev.c
+++ b/arch/x86/virt/svm/sev.c
@@ -542,3 +542,23 @@ u64 snp_config_transaction_end(void)
 	return id;
 }
 EXPORT_SYMBOL_GPL(snp_config_transaction_end);
+
+u64 snp_config_transaction_get_id(void)
+{
+	return snp_transaction_id;
+}
+EXPORT_SYMBOL_GPL(snp_config_transaction_get_id);
+
+bool snp_config_transaction_is_stale(u64 id)
+{
+	bool stale = false;
+
+	mutex_lock(&snp_transaction_lock);
+	if (snp_transaction_pending ||
+	    id != snp_transaction_id)
+		stale = true;
+	mutex_unlock(&snp_transaction_lock);
+
+	return stale;
+}
+EXPORT_SYMBOL_GPL(snp_config_transaction_is_stale);
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index e0599144387b..fe8994b95de9 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -170,6 +170,7 @@ struct kvm_xen_exit {
 struct kvm_user_vmgexit {
 #define KVM_USER_VMGEXIT_PSC_MSR	1
 #define KVM_USER_VMGEXIT_PSC		2
+#define KVM_USER_VMGEXIT_EXT_GUEST_REQ	3
 	__u32 type; /* KVM_USER_VMGEXIT_* type */
 	union {
 		struct {
@@ -183,6 +184,11 @@ struct kvm_user_vmgexit {
 			__u64 shared_gpa;
 			__u64 ret;
 		} psc;
+		struct {
+			__u64 data_gpa;
+			__u64 data_npages;
+			__u32 ret;
+		} ext_guest_req;
 	};
 };
 
-- 
2.25.1