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

[Peter Gonda <pgonda@google.com>]

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
>