[PATCH Part1 RFC v4 36/36] virt: sevguest: Add support to get extended report

Brijesh Singh
2021-07-07T18:18:20Z

Version 2 of GHCB specification defines NAE to get the extended guest
request. It is similar to the SNP_GET_REPORT ioctl. The main difference
is related to the additional data that 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@amd.com>
---
Documentation/virt/coco/sevguest.rst | 22 +++++
drivers/virt/coco/sevguest/sevguest.c | 126 ++++++++++++++++++++++++++
include/uapi/linux/sev-guest.h | 13 +++
3 files changed, 161 insertions(+)

diff --git a/Documentation/virt/coco/sevguest.rst b/Documentation/virt/coco/sevguest.rst
index 25446670d816..7acb8696fca4 100644
--- a/Documentation/virt/coco/sevguest.rst
+++ b/Documentation/virt/coco/sevguest.rst
@@ -85,3 +85,25 @@ on the various fileds passed in the key derivation request.

On success, the snp_derived_key_resp.data will contains the derived key
value.
+
+2.2 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 contains the attestation report
+and snp_ext_report_req.certs_address will contains the certificate blob. If the
+length of the blob is lesser 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.
diff --git a/drivers/virt/coco/sevguest/sevguest.c b/drivers/virt/coco/sevguest/sevguest.c
index 2f20db80490a..d39667a62002 100644
--- a/drivers/virt/coco/sevguest/sevguest.c
+++ b/drivers/virt/coco/sevguest/sevguest.c
@@ -39,6 +39,7 @@ struct snp_guest_dev {
struct device *dev;
struct miscdevice misc;

+ void *certs_data;
struct snp_guest_crypto *crypto;
struct snp_guest_msg *request, *response;
};
@@ -348,6 +349,117 @@ static int get_derived_key(struct snp_guest_dev *snp_dev, struct snp_user_guest_
return rc;
}

+static int get_ext_report(struct snp_guest_dev *snp_dev, struct snp_user_guest_request *arg)
+{
+ struct snp_guest_crypto *crypto = snp_dev->crypto;
+ struct snp_guest_request_data input = {};
+ struct snp_ext_report_req req;
+ int ret, npages = 0, resp_len;
+ struct snp_report_resp *resp;
+ struct snp_report_req *rreq;
+ unsigned long fw_err = 0;
+
+ if (!arg->req_data || !arg->resp_data)
+ return -EINVAL;
+
+ /* Copy the request payload from the userspace */
+ if (copy_from_user(&req, (void __user *)arg->req_data, sizeof(req)))
+ return -EFAULT;
+
+ rreq = &req.data;
+
+ /* Message version must be non-zero */
+ if (!rreq->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 we copy
+ * zeros to indicate that certificate data was not provided.
+ */
+ memset(snp_dev->certs_data, 0, req.certs_len);
+
+ input.data_gpa = __pa(snp_dev->certs_data);
+ 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;
+
+ if (copy_from_user(resp, (void __user *)arg->resp_data, sizeof(*resp))) {
+ ret = -EFAULT;
+ goto e_free;
+ }
+
+ /* Encrypt the userspace provided payload */
+ ret = enc_payload(snp_dev, rreq->msg_version, SNP_MSG_REPORT_REQ,
+ &rreq->user_data, sizeof(rreq->user_data));
+ if (ret)
+ goto e_free;
+
+ /* Call firmware to process the request */
+ input.req_gpa = __pa(snp_dev->request);
+ input.resp_gpa = __pa(snp_dev->response);
+ input.data_npages = npages;
+ memset(snp_dev->response, 0, sizeof(*snp_dev->response));
+ ret = snp_issue_guest_request(EXT_GUEST_REQUEST, &input, &fw_err);
+
+ /* Popogate any firmware error to the userspace */
+ arg->fw_err = fw_err;
+
+ /* If certs length is invalid then copy the returned length */
+ if (arg->fw_err == SNP_GUEST_REQ_INVALID_LEN) {
+ req.certs_len = input.data_npages << PAGE_SHIFT;
+
+ if (copy_to_user((void __user *)arg->req_data, &req, sizeof(req)))
+ ret = -EFAULT;
+
+ goto e_free;
+ }
+
+ if (ret)
+ goto e_free;
+
+ /* Decrypt the response payload */
+ ret = verify_and_dec_payload(snp_dev, resp->data, resp_len);
+ if (ret)
+ goto e_free;
+
+ /* Copy the certificate data blob to userspace */
+ if (req.certs_address &&
+ 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);
@@ -369,6 +481,10 @@ static long snp_guest_ioctl(struct file *file, unsigned int ioctl, unsigned long
ret = get_derived_key(snp_dev, &input);
break;
}
+ case SNP_GET_EXT_REPORT: {
+ ret = get_ext_report(snp_dev, &input);
+ break;
+ }
default:
break;
}
@@ -454,6 +570,12 @@ static int __init snp_guest_probe(struct platform_device *pdev)
goto e_free_req;
}

+ snp_dev->certs_data = alloc_shared_pages(SEV_FW_BLOB_MAX_SIZE);
+ if (IS_ERR(snp_dev->certs_data)) {
+ ret = PTR_ERR(snp_dev->certs_data);
+ goto e_free_resp;
+ }
+
misc = &snp_dev->misc;
misc->minor = MISC_DYNAMIC_MINOR;
misc->name = DEVICE_NAME;
@@ -461,6 +583,9 @@ static int __init snp_guest_probe(struct platform_device *pdev)

return misc_register(misc);

+e_free_resp:
+ free_shared_pages(snp_dev->response, sizeof(struct snp_guest_msg));
+
e_free_req:
free_shared_pages(snp_dev->request, sizeof(struct snp_guest_msg));

@@ -476,6 +601,7 @@ 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 621a9167df7a..23659215fcfb 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_user_guest_request)

+/* 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_user_guest_request)
+
#endif /* __UAPI_LINUX_SEV_GUEST_H_ */
--
2.17.1