virt: sevguest: Add support to get extended report

Version 2 of GHCB specification defines Non-Automatic-Exit (NAE) to get
extended guest report which is similar to the SNP_GET_REPORT ioctl. The
main difference is related to the additional data that will be returned.

That 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.

  [ bp: Massage commit message, cast 1st arg of access_ok() ]

Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lore.kernel.org/r/20220307213356.2797205-46-brijesh.singh@amd.com

Documentation/virt/coco/sevguest.rst

@@ -95,6 +95,29 @@ on the various fields passed in the key derivation request.
 On success, the snp_derived_key_resp.data 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
 ---------
 

drivers/virt/coco/sevguest/sevguest.c

@@ -43,6 +43,7 @@ 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;
@@ -433,6 +434,82 @@ 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;
+
+	lockdep_assert_held(&snp_cmd_mutex);
+
+	if (!arg->req_data || !arg->resp_data)
+		return -EINVAL;
+
+	if (copy_from_user(&req, (void __user *)arg->req_data, sizeof(req)))
+		return -EFAULT;
+
+	/* userspace does not want certificate data */
+	if (!req.certs_len || !req.certs_address)
+		goto cmd;
+
+	if (req.certs_len > SEV_FW_BLOB_MAX_SIZE ||
+	    !IS_ALIGNED(req.certs_len, PAGE_SIZE))
+		return -EINVAL;
+
+	if (!access_ok((const void __user *)req.certs_address, req.certs_len))
+		return -EFAULT;
+
+	/*
+	 * Initialize the intermediate buffer with all zeros. 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;
+cmd:
+	/*
+	 * 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, arg->msg_version,
+				   SNP_MSG_REPORT_REQ, &req.data,
+				   sizeof(req.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;
+
+	if (npages &&
+	    copy_to_user((void __user *)req.certs_address, snp_dev->certs_data,
+			 req.certs_len)) {
+		ret = -EFAULT;
+		goto e_free;
+	}
+
+	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);
@@ -465,6 +542,9 @@ 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;
 	}
@@ -595,10 +675,14 @@ static int __init snp_guest_probe(struct platform_device *pdev)
 	if (!snp_dev->response)
 		goto e_free_request;
 
+	snp_dev->certs_data = alloc_shared_pages(SEV_FW_BLOB_MAX_SIZE);
+	if (!snp_dev->certs_data)
+		goto e_free_response;
+
 	ret = -EIO;
 	snp_dev->crypto = init_crypto(snp_dev, snp_dev->vmpck, VMPCK_KEY_LEN);
 	if (!snp_dev->crypto)
-		goto e_free_response;
+		goto e_free_cert_data;
 
 	misc = &snp_dev->misc;
 	misc->minor = MISC_DYNAMIC_MINOR;
@@ -608,14 +692,17 @@ 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)
-		goto e_free_response;
+		goto e_free_cert_data;
 
 	dev_info(dev, "Initialized SNP guest driver (using vmpck_id %d)\n", vmpck_id);
 	return 0;
 
+e_free_cert_data:
+	free_shared_pages(snp_dev->certs_data, SEV_FW_BLOB_MAX_SIZE);
 e_free_response:
 	free_shared_pages(snp_dev->response, sizeof(struct snp_guest_msg));
 e_free_request:
@@ -629,6 +716,7 @@ static int __exit snp_guest_remove(struct platform_device *pdev)
 {
 	struct snp_guest_dev *snp_dev = platform_get_drvdata(pdev);
 
+	free_shared_pages(snp_dev->certs_data, SEV_FW_BLOB_MAX_SIZE);
 	free_shared_pages(snp_dev->response, sizeof(struct snp_guest_msg));
 	free_shared_pages(snp_dev->request, sizeof(struct snp_guest_msg));
 	deinit_crypto(snp_dev->crypto);

include/uapi/linux/sev-guest.h

@@ -56,6 +56,16 @@ struct snp_guest_request_ioctl {
 	__u64 fw_err;
 };
 
+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 */
@@ -64,4 +74,7 @@ struct snp_guest_request_ioctl {
 /* 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_ */