KVM/SVM: add support for SEV attestation command

The SEV FW version >= 0.23 added a new command that can be used to query
the attestation report containing the SHA-256 digest of the guest memory
encrypted through the KVM_SEV_LAUNCH_UPDATE_{DATA, VMSA} commands and
sign the report with the Platform Endorsement Key (PEK).

See the SEV FW API spec section 6.8 for more details.

Note there already exist a command (KVM_SEV_LAUNCH_MEASURE) that can be
used to get the SHA-256 digest. The main difference between the
KVM_SEV_LAUNCH_MEASURE and KVM_SEV_ATTESTATION_REPORT is that the latter
can be called while the guest is running and the measurement value is
signed with PEK.

Cc: James Bottomley <jejb@linux.ibm.com>
Cc: Tom Lendacky <Thomas.Lendacky@amd.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Sean Christopherson <seanjc@google.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: John Allen <john.allen@amd.com>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: linux-crypto@vger.kernel.org
Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
Acked-by: David Rientjes <rientjes@google.com>
Tested-by: James Bottomley <jejb@linux.ibm.com>
Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
Message-Id: <20210104151749.30248-1-brijesh.singh@amd.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Documentation/virt/kvm/amd-memory-encryption.rst

@@ -263,6 +263,27 @@ Returns: 0 on success, -negative on error
                 __u32 trans_len;
         };
 
+10. KVM_SEV_GET_ATTESTATION_REPORT
+----------------------------------
+
+The KVM_SEV_GET_ATTESTATION_REPORT command can be used by the hypervisor to query the attestation
+report containing the SHA-256 digest of the guest memory and VMSA passed through the KVM_SEV_LAUNCH
+commands and signed with the PEK. The digest returned by the command should match the digest
+used by the guest owner with the KVM_SEV_LAUNCH_MEASURE.
+
+Parameters (in): struct kvm_sev_attestation
+
+Returns: 0 on success, -negative on error
+
+::
+
+        struct kvm_sev_attestation_report {
+                __u8 mnonce[16];        /* A random mnonce that will be placed in the report */
+
+                __u64 uaddr;            /* userspace address where the report should be copied */
+                __u32 len;
+        };
+
 References
 ==========
 

arch/x86/kvm/svm/sev.c

@@ -1041,6 +1041,74 @@ e_unpin_memory:
 	return ret;
 }
 
+static int sev_get_attestation_report(struct kvm *kvm, struct kvm_sev_cmd *argp)
+{
+	void __user *report = (void __user *)(uintptr_t)argp->data;
+	struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
+	struct sev_data_attestation_report *data;
+	struct kvm_sev_attestation_report params;
+	void __user *p;
+	void *blob = NULL;
+	int ret;
+
+	if (!sev_guest(kvm))
+		return -ENOTTY;
+
+	if (copy_from_user(&params, (void __user *)(uintptr_t)argp->data, sizeof(params)))
+		return -EFAULT;
+
+	data = kzalloc(sizeof(*data), GFP_KERNEL_ACCOUNT);
+	if (!data)
+		return -ENOMEM;
+
+	/* User wants to query the blob length */
+	if (!params.len)
+		goto cmd;
+
+	p = (void __user *)(uintptr_t)params.uaddr;
+	if (p) {
+		if (params.len > SEV_FW_BLOB_MAX_SIZE) {
+			ret = -EINVAL;
+			goto e_free;
+		}
+
+		ret = -ENOMEM;
+		blob = kmalloc(params.len, GFP_KERNEL);
+		if (!blob)
+			goto e_free;
+
+		data->address = __psp_pa(blob);
+		data->len = params.len;
+		memcpy(data->mnonce, params.mnonce, sizeof(params.mnonce));
+	}
+cmd:
+	data->handle = sev->handle;
+	ret = sev_issue_cmd(kvm, SEV_CMD_ATTESTATION_REPORT, data, &argp->error);
+	/*
+	 * If we query the session length, FW responded with expected data.
+	 */
+	if (!params.len)
+		goto done;
+
+	if (ret)
+		goto e_free_blob;
+
+	if (blob) {
+		if (copy_to_user(p, blob, params.len))
+			ret = -EFAULT;
+	}
+
+done:
+	params.len = data->len;
+	if (copy_to_user(report, &params, sizeof(params)))
+		ret = -EFAULT;
+e_free_blob:
+	kfree(blob);
+e_free:
+	kfree(data);
+	return ret;
+}
+
 int svm_mem_enc_op(struct kvm *kvm, void __user *argp)
 {
 	struct kvm_sev_cmd sev_cmd;
@@ -1091,6 +1159,9 @@ int svm_mem_enc_op(struct kvm *kvm, void __user *argp)
 	case KVM_SEV_LAUNCH_SECRET:
 		r = sev_launch_secret(kvm, &sev_cmd);
 		break;
+	case KVM_SEV_GET_ATTESTATION_REPORT:
+		r = sev_get_attestation_report(kvm, &sev_cmd);
+		break;
 	default:
 		r = -EINVAL;
 		goto out;

drivers/crypto/ccp/sev-dev.c

@@ -128,6 +128,7 @@ static int sev_cmd_buffer_len(int cmd)
 	case SEV_CMD_LAUNCH_UPDATE_SECRET:	return sizeof(struct sev_data_launch_secret);
 	case SEV_CMD_DOWNLOAD_FIRMWARE:		return sizeof(struct sev_data_download_firmware);
 	case SEV_CMD_GET_ID:			return sizeof(struct sev_data_get_id);
+	case SEV_CMD_ATTESTATION_REPORT:	return sizeof(struct sev_data_attestation_report);
 	default:				return 0;
 	}
 

include/linux/psp-sev.h

@@ -66,6 +66,7 @@ enum sev_cmd {
 	SEV_CMD_LAUNCH_MEASURE		= 0x033,
 	SEV_CMD_LAUNCH_UPDATE_SECRET	= 0x034,
 	SEV_CMD_LAUNCH_FINISH		= 0x035,
+	SEV_CMD_ATTESTATION_REPORT	= 0x036,
 
 	/* Guest migration commands (outgoing) */
 	SEV_CMD_SEND_START		= 0x040,
@@ -483,6 +484,22 @@ struct sev_data_dbg {
 	u32 len;				/* In */
 } __packed;
 
+/**
+ * struct sev_data_attestation_report - SEV_ATTESTATION_REPORT command parameters
+ *
+ * @handle: handle of the VM
+ * @mnonce: a random nonce that will be included in the report.
+ * @address: physical address where the report will be copied.
+ * @len: length of the physical buffer.
+ */
+struct sev_data_attestation_report {
+	u32 handle;				/* In */
+	u32 reserved;
+	u64 address;				/* In */
+	u8 mnonce[16];				/* In */
+	u32 len;				/* In/Out */
+} __packed;
+
 #ifdef CONFIG_CRYPTO_DEV_SP_PSP
 
 /**

include/uapi/linux/kvm.h

@@ -1593,6 +1593,8 @@ enum sev_cmd_id {
 	KVM_SEV_DBG_ENCRYPT,
 	/* Guest certificates commands */
 	KVM_SEV_CERT_EXPORT,
+	/* Attestation report */
+	KVM_SEV_GET_ATTESTATION_REPORT,
 
 	KVM_SEV_NR_MAX,
 };
@@ -1645,6 +1647,12 @@ struct kvm_sev_dbg {
 	__u32 len;
 };
 
+struct kvm_sev_attestation_report {
+	__u8 mnonce[16];
+	__u64 uaddr;
+	__u32 len;
+};
+
 #define KVM_DEV_ASSIGN_ENABLE_IOMMU	(1 << 0)
 #define KVM_DEV_ASSIGN_PCI_2_3		(1 << 1)
 #define KVM_DEV_ASSIGN_MASK_INTX	(1 << 2)