Re: [PATCH v9 43/43] virt: sevguest: Add support to get extended report

Peter Gonda
2022-02-01T20:44:11Z

On Fri, Jan 28, 2022 at 10:19 AM Brijesh Singh <brijesh.singh@amd.com> wrote:
>
> 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 | 89 +++++++++++++++++++++++++++
> include/uapi/linux/sev-guest.h | 13 ++++
> 3 files changed, 125 insertions(+)
>
> diff --git a/Documentation/virt/coco/sevguest.rst b/Documentation/virt/coco/sevguest.rst
> index aafc9bce9aef..b9fe20e92d06 100644
> --- a/Documentation/virt/coco/sevguest.rst
> +++ b/Documentation/virt/coco/sevguest.rst
> @@ -90,6 +90,29 @@ 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
> ---------
>
> diff --git a/drivers/virt/coco/sevguest/sevguest.c b/drivers/virt/coco/sevguest/sevguest.c
> index 4369e55df9a6..a53854353944 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;
> @@ -434,6 +435,84 @@ 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 = {0};
> + 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;
> +
> + 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

zeros

> + * 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;

Can we pull this duplicated code from get_report() into a helper?

> +
> + 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;
> +
> + /* 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 +545,9 @@ 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 +676,10 @@ 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 +693,7 @@ 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 +704,7 @@ 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 +717,7 @@ 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 bcd00a6d4501..0a47b6627c78 100644
> --- a/include/uapi/linux/sev-guest.h
> +++ b/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_ */
> --
> 2.25.1
>