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Subject[PATCH v7 45/45] virt: sevguest: Add support to get extended report
Date
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@amd.com>
---
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
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