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    Subject[tip: x86/sev] virt: sevguest: Add support to get extended report
    The following commit has been merged into the x86/sev branch of tip:

    Commit-ID: d80b494f712317493d464a55652698c4d1b7bb0f
    Gitweb: https://git.kernel.org/tip/d80b494f712317493d464a55652698c4d1b7bb0f
    Author: Brijesh Singh <brijesh.singh@amd.com>
    AuthorDate: Mon, 07 Mar 2022 15:33:55 -06:00
    Committer: Borislav Petkov <bp@suse.de>
    CommitterDate: Thu, 07 Apr 2022 16:47:12 +02:00

    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 | 23 +++++++-
    drivers/virt/coco/sevguest/sevguest.c | 92 +++++++++++++++++++++++++-
    include/uapi/linux/sev-guest.h | 13 ++++-
    3 files changed, 126 insertions(+), 2 deletions(-)

    diff --git a/Documentation/virt/coco/sevguest.rst b/Documentation/virt/coco/sevguest.rst
    index 4135c14..625de22 100644
    --- a/Documentation/virt/coco/sevguest.rst
    +++ b/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
    ---------

    diff --git a/drivers/virt/coco/sevguest/sevguest.c b/drivers/virt/coco/sevguest/sevguest.c
    index 393777b..15afb6c 100644
    --- a/drivers/virt/coco/sevguest/sevguest.c
    +++ b/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);
    diff --git a/include/uapi/linux/sev-guest.h b/include/uapi/linux/sev-guest.h
    index 598367f..256aaef 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_ */
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