[PATCH v7 45/45] virt: sevguest: Add support to get extended report

[Brijesh Singh]

Version 2 of GHCB specification defines Non-Automatic-Exit(NAE) to get
the extended guest report. It is similar to the SNP_GET_REPORT ioctl.
The main difference is related to the additional data that will be
returned. The additional data returned is a certificate blob that can
be used by the SNP guest user. The certificate blob layout is defined
in the GHCB specification. The driver simply treats the blob as a opaque
data and copies it to userspace.

Signed-off-by: Brijesh Singh <brijesh.singh@xxxxxxx>
---
 Documentation/virt/coco/sevguest.rst  | 23 +++++++
 drivers/virt/coco/sevguest/sevguest.c | 93 +++++++++++++++++++++++++++
 include/uapi/linux/sev-guest.h        | 13 ++++
 3 files changed, 129 insertions(+)

diff --git a/Documentation/virt/coco/sevguest.rst b/Documentation/virt/coco/sevguest.rst
index 0bd9a65e0370..5217a9176fb9 100644
--- a/Documentation/virt/coco/sevguest.rst
+++ b/Documentation/virt/coco/sevguest.rst
@@ -86,6 +86,29 @@ on the various fields passed in the key derivation request.
 On success, the snp_derived_key_resp.data will contains the derived key value. See
 the SEV-SNP specification for further details.
 
+
+2.3 SNP_GET_EXT_REPORT
+----------------------
+:Technology: sev-snp
+:Type: guest ioctl
+:Parameters (in/out): struct snp_ext_report_req
+:Returns (out): struct snp_report_resp on success, -negative on error
+
+The SNP_GET_EXT_REPORT ioctl is similar to the SNP_GET_REPORT. The difference is
+related to the additional certificate data that is returned with the report.
+The certificate data returned is being provided by the hypervisor through the
+SNP_SET_EXT_CONFIG.
+
+The ioctl uses the SNP_GUEST_REQUEST (MSG_REPORT_REQ) command provided by the SEV-SNP
+firmware to get the attestation report.
+
+On success, the snp_ext_report_resp.data will contain the attestation report
+and snp_ext_report_req.certs_address will contain the certificate blob. If the
+length of the blob is smaller than expected then snp_ext_report_req.certs_len will
+be updated with the expected value.
+
+See GHCB specification for further detail on how to parse the certificate blob.
+
 Reference
 ---------
 
diff --git a/drivers/virt/coco/sevguest/sevguest.c b/drivers/virt/coco/sevguest/sevguest.c
index bece6856573e..15e37f3a0bb1 100644
--- a/drivers/virt/coco/sevguest/sevguest.c
+++ b/drivers/virt/coco/sevguest/sevguest.c
@@ -41,6 +41,7 @@ struct snp_guest_dev {
 	struct device *dev;
 	struct miscdevice misc;
 
+	void *certs_data;
 	struct snp_guest_crypto *crypto;
 	struct snp_guest_msg *request, *response;
 	struct snp_secrets_page_layout *layout;
@@ -438,6 +439,88 @@ static int get_derived_key(struct snp_guest_dev *snp_dev, struct snp_guest_reque
 	return rc;
 }
 
+static int get_ext_report(struct snp_guest_dev *snp_dev, struct snp_guest_request_ioctl *arg)
+{
+	struct snp_guest_crypto *crypto = snp_dev->crypto;
+	struct snp_ext_report_req req;
+	struct snp_report_resp *resp;
+	int ret, npages = 0, resp_len;
+
+	if (!arg->req_data || !arg->resp_data)
+		return -EINVAL;
+
+	/* Copy the request payload from userspace */
+	if (copy_from_user(&req, (void __user *)arg->req_data, sizeof(req)))
+		return -EFAULT;
+
+	/* Message version must be non-zero */
+	if (!req.data.msg_version)
+		return -EINVAL;
+
+	if (req.certs_len) {
+		if (req.certs_len > SEV_FW_BLOB_MAX_SIZE ||
+		    !IS_ALIGNED(req.certs_len, PAGE_SIZE))
+			return -EINVAL;
+	}
+
+	if (req.certs_address && req.certs_len) {
+		if (!access_ok(req.certs_address, req.certs_len))
+			return -EFAULT;
+
+		/*
+		 * Initialize the intermediate buffer with all zero's. This buffer
+		 * is used in the guest request message to get the certs blob from
+		 * the host. If host does not supply any certs in it, then copy
+		 * zeros to indicate that certificate data was not provided.
+		 */
+		memset(snp_dev->certs_data, 0, req.certs_len);
+
+		npages = req.certs_len >> PAGE_SHIFT;
+	}
+
+	/*
+	 * The intermediate response buffer is used while decrypting the
+	 * response payload. Make sure that it has enough space to cover the
+	 * authtag.
+	 */
+	resp_len = sizeof(resp->data) + crypto->a_len;
+	resp = kzalloc(resp_len, GFP_KERNEL_ACCOUNT);
+	if (!resp)
+		return -ENOMEM;
+
+	snp_dev->input.data_npages = npages;
+	ret = handle_guest_request(snp_dev, SVM_VMGEXIT_EXT_GUEST_REQUEST, req.data.msg_version,
+				   SNP_MSG_REPORT_REQ, &req.data.user_data,
+				   sizeof(req.data.user_data), resp->data, resp_len, &arg->fw_err);
+
+	/* If certs length is invalid then copy the returned length */
+	if (arg->fw_err == SNP_GUEST_REQ_INVALID_LEN) {
+		req.certs_len = snp_dev->input.data_npages << PAGE_SHIFT;
+
+		if (copy_to_user((void __user *)arg->req_data, &req, sizeof(req)))
+			ret = -EFAULT;
+	}
+
+	if (ret)
+		goto e_free;
+
+	/* Copy the certificate data blob to userspace */
+	if (req.certs_address && req.certs_len &&
+	    copy_to_user((void __user *)req.certs_address, snp_dev->certs_data,
+			 req.certs_len)) {
+		ret = -EFAULT;
+		goto e_free;
+	}
+
+	/* Copy the response payload to userspace */
+	if (copy_to_user((void __user *)arg->resp_data, resp, sizeof(*resp)))
+		ret = -EFAULT;
+
+e_free:
+	kfree(resp);
+	return ret;
+}
+
 static long snp_guest_ioctl(struct file *file, unsigned int ioctl, unsigned long arg)
 {
 	struct snp_guest_dev *snp_dev = to_snp_dev(file);
@@ -466,6 +549,9 @@ static long snp_guest_ioctl(struct file *file, unsigned int ioctl, unsigned long
 	case SNP_GET_DERIVED_KEY:
 		ret = get_derived_key(snp_dev, &input);
 		break;
+	case SNP_GET_EXT_REPORT:
+		ret = get_ext_report(snp_dev, &input);
+		break;
 	default:
 		break;
 	}
@@ -594,6 +680,10 @@ static int __init snp_guest_probe(struct platform_device *pdev)
 	if (!snp_dev->response)
 		goto e_fail;
 
+	snp_dev->certs_data = alloc_shared_pages(SEV_FW_BLOB_MAX_SIZE);
+	if (!snp_dev->certs_data)
+		goto e_fail;
+
 	ret = -EIO;
 	snp_dev->crypto = init_crypto(snp_dev, snp_dev->vmpck, VMPCK_KEY_LEN);
 	if (!snp_dev->crypto)
@@ -607,6 +697,7 @@ static int __init snp_guest_probe(struct platform_device *pdev)
 	/* initial the input address for guest request */
 	snp_dev->input.req_gpa = __pa(snp_dev->request);
 	snp_dev->input.resp_gpa = __pa(snp_dev->response);
+	snp_dev->input.data_gpa = __pa(snp_dev->certs_data);
 
 	ret =  misc_register(misc);
 	if (ret)
@@ -617,6 +708,7 @@ static int __init snp_guest_probe(struct platform_device *pdev)
 
 e_fail:
 	iounmap(layout);
+	free_shared_pages(snp_dev->certs_data, SEV_FW_BLOB_MAX_SIZE);
 	free_shared_pages(snp_dev->request, sizeof(struct snp_guest_msg));
 	free_shared_pages(snp_dev->response, sizeof(struct snp_guest_msg));
 
@@ -629,6 +721,7 @@ static int __exit snp_guest_remove(struct platform_device *pdev)
 
 	free_shared_pages(snp_dev->request, sizeof(struct snp_guest_msg));
 	free_shared_pages(snp_dev->response, sizeof(struct snp_guest_msg));
+	free_shared_pages(snp_dev->certs_data, SEV_FW_BLOB_MAX_SIZE);
 	deinit_crypto(snp_dev->crypto);
 	misc_deregister(&snp_dev->misc);
 
diff --git a/include/uapi/linux/sev-guest.h b/include/uapi/linux/sev-guest.h
index f6d9c136ff4d..3f6a9d694a47 100644
--- a/include/uapi/linux/sev-guest.h
+++ b/include/uapi/linux/sev-guest.h
@@ -57,6 +57,16 @@ struct snp_derived_key_resp {
 	__u8 data[64];
 };
 
+struct snp_ext_report_req {
+	struct snp_report_req data;
+
+	/* where to copy the certificate blob */
+	__u64 certs_address;
+
+	/* length of the certificate blob */
+	__u32 certs_len;
+};
+
 #define SNP_GUEST_REQ_IOC_TYPE	'S'
 
 /* Get SNP attestation report */
@@ -65,4 +75,7 @@ struct snp_derived_key_resp {
 /* Get a derived key from the root */
 #define SNP_GET_DERIVED_KEY _IOWR(SNP_GUEST_REQ_IOC_TYPE, 0x1, struct snp_guest_request_ioctl)
 
+/* Get SNP extended report as defined in the GHCB specification version 2. */
+#define SNP_GET_EXT_REPORT _IOWR(SNP_GUEST_REQ_IOC_TYPE, 0x2, struct snp_guest_request_ioctl)
+
 #endif /* __UAPI_LINUX_SEV_GUEST_H_ */
-- 
2.25.1