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virt: sevguest: Add support to get extended report

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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
This commit is contained in:
Brijesh Singh 2022-03-07 15:33:55 -06:00 committed by Borislav Petkov
parent 68de0b2f93
commit d80b494f71
3 changed files with 126 additions and 2 deletions
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23
Documentation/virt/coco/sevguest.rst
View File

@ -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
---------

92
drivers/virt/coco/sevguest/sevguest.c
View File

@ -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);

13
include/uapi/linux/sev-guest.h
View File

@ -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_ */