Re: [PATCH Part2 v5 17/45] crypto: ccp: Add the SNP_{SET,GET}_EXT_CONFIG command

Marc Orr
2021-09-10T03:28:11Z

`

On Fri, Aug 20, 2021 at 9:00 AM Brijesh Singh <brijesh.singh@amd.com> wrote:
>
> The SEV-SNP firmware provides the SNP_CONFIG command used to set the
> system-wide configuration value for SNP guests. The information includes
> the TCB version string to be reported in guest attestation reports.
>
> Version 2 of the GHCB specification adds an NAE (SNP extended guest
> request) that a guest can use to query the reports that include additional
> certificates.
>
> In both cases, userspace provided additional data is included in the
> attestation reports. The userspace will use the SNP_SET_EXT_CONFIG
> command to give the certificate blob and the reported TCB version string
> at once. Note that the specification defines certificate blob with a
> specific GUID format; the userspace is responsible for building the
> proper certificate blob. The ioctl treats it an opaque blob.
>
> While it is not defined in the spec, but let's add SNP_GET_EXT_CONFIG
> command that can be used to obtain the data programmed through the
> SNP_SET_EXT_CONFIG.
>
> Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
> ---
> Documentation/virt/coco/sevguest.rst | 28 +++++++
> drivers/crypto/ccp/sev-dev.c | 115 +++++++++++++++++++++++++++
> drivers/crypto/ccp/sev-dev.h | 3 +
> include/uapi/linux/psp-sev.h | 17 ++++
> 4 files changed, 163 insertions(+)
>
> diff --git a/Documentation/virt/coco/sevguest.rst b/Documentation/virt/coco/sevguest.rst
> index 7c51da010039..64a1b5167b33 100644
> --- a/Documentation/virt/coco/sevguest.rst
> +++ b/Documentation/virt/coco/sevguest.rst
> @@ -134,3 +134,31 @@ See GHCB specification for further detail on how to parse the certificate blob.
> The SNP_PLATFORM_STATUS command is used to query the SNP platform status. The
> status includes API major, minor version and more. See the SEV-SNP
> specification for further details.
> +
> +2.4 SNP_SET_EXT_CONFIG
> +----------------------
> +:Technology: sev-snp
> +:Type: hypervisor ioctl cmd
> +:Parameters (in): struct sev_data_snp_ext_config
> +:Returns (out): 0 on success, -negative on error
> +
> +The SNP_SET_EXT_CONFIG is used to set the system-wide configuration such as
> +reported TCB version in the attestation report. The command is similar to
> +SNP_CONFIG command defined in the SEV-SNP spec. The main difference is the
> +command also accepts an additional certificate blob defined in the GHCB
> +specification.
> +
> +If the certs_address is zero, then previous certificate blob will deleted.
> +For more information on the certificate blob layout, see the GHCB spec
> +(extended guest request message).
> +
> +
> +2.4 SNP_GET_EXT_CONFIG
> +----------------------
> +:Technology: sev-snp
> +:Type: hypervisor ioctl cmd
> +:Parameters (in): struct sev_data_snp_ext_config
> +:Returns (out): 0 on success, -negative on error
> +
> +The SNP_SET_EXT_CONFIG is used to query the system-wide configuration set
> +through the SNP_SET_EXT_CONFIG.
> diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c
> index 16c6df5d412c..9ba194acbe85 100644
> --- a/drivers/crypto/ccp/sev-dev.c
> +++ b/drivers/crypto/ccp/sev-dev.c
> @@ -1132,6 +1132,10 @@ static int __sev_snp_shutdown_locked(int *error)
> if (!sev->snp_inited)
> return 0;
>
> + /* Free the memory used for caching the certificate data */
> + kfree(sev->snp_certs_data);
> + sev->snp_certs_data = NULL;
> +
> /* SHUTDOWN requires the DF_FLUSH */
> wbinvd_on_all_cpus();
> __sev_do_cmd_locked(SEV_CMD_SNP_DF_FLUSH, NULL, NULL);
> @@ -1436,6 +1440,111 @@ static int sev_ioctl_snp_platform_status(struct sev_issue_cmd *argp)
> return ret;
> }
>
> +static int sev_ioctl_snp_get_config(struct sev_issue_cmd *argp)
> +{
> + struct sev_device *sev = psp_master->sev_data;
> + struct sev_user_data_ext_snp_config input;
> + int ret;
> +
> + if (!sev->snp_inited || !argp->data)
> + return -EINVAL;
> +
> + if (copy_from_user(&input, (void __user *)argp->data, sizeof(input)))
> + return -EFAULT;
> +
> + /* Copy the TCB version programmed through the SET_CONFIG to userspace */
> + if (input.config_address) {
> + if (copy_to_user((void * __user)input.config_address,
> + &sev->snp_config, sizeof(struct sev_user_data_snp_config)))
> + return -EFAULT;
> + }
> +
> + /* Copy the extended certs programmed through the SNP_SET_CONFIG */
> + if (input.certs_address && sev->snp_certs_data) {
> + if (input.certs_len < sev->snp_certs_len) {
> + /* Return the certs length to userspace */
> + input.certs_len = sev->snp_certs_len;

This API to retrieve the length of the certs seems pretty odd. We only
return the length if the input.certs_address is non-NULL. But if we
know the length how did we allocate an address to write to
`input.certs_address`?

> +
> + ret = -ENOSR;
> + goto e_done;
> + }
> +
> + if (copy_to_user((void * __user)input.certs_address,
> + sev->snp_certs_data, sev->snp_certs_len))
> + return -EFAULT;
> + }
> +
> + ret = 0;
> +
> +e_done:
> + if (copy_to_user((void __user *)argp->data, &input, sizeof(input)))
> + ret = -EFAULT;
> +
> + return ret;
> +}
> +
> +static int sev_ioctl_snp_set_config(struct sev_issue_cmd *argp, bool writable)
> +{
> + struct sev_device *sev = psp_master->sev_data;
> + struct sev_user_data_ext_snp_config input;
> + struct sev_user_data_snp_config config;
> + void *certs = NULL;
> + int ret = 0;
> +
> + if (!sev->snp_inited || !argp->data)
> + return -EINVAL;
> +
> + if (!writable)
> + return -EPERM;
> +
> + if (copy_from_user(&input, (void __user *)argp->data, sizeof(input)))
> + return -EFAULT;
> +
> + /* Copy the certs from userspace */
> + if (input.certs_address) {
> + if (!input.certs_len || !IS_ALIGNED(input.certs_len, PAGE_SIZE))
> + return -EINVAL;
> +
> + certs = psp_copy_user_blob(input.certs_address, input.certs_len);

Is `psp_copy_user_blob()` implemented in this patch series? When I
searched through the patches, I only found an implementation that
always returns an error. But maybe I missed the implementation?

Also, out of curiosity, any reason we cannot use copy_from_user here?

> + if (IS_ERR(certs))
> + return PTR_ERR(certs);
> + }
> +
> + /* Issue the PSP command to update the TCB version using the SNP_CONFIG. */
> + if (input.config_address) {
> + if (copy_from_user(&config,
> + (void __user *)input.config_address, sizeof(config))) {
> + ret = -EFAULT;
> + goto e_free;
> + }
> +
> + ret = __sev_do_cmd_locked(SEV_CMD_SNP_CONFIG, &config, &argp->error);
> + if (ret)
> + goto e_free;
> +
> + memcpy(&sev->snp_config, &config, sizeof(config));
> + }
> +
> + /*
> + * If the new certs are passed then cache it else free the old certs.
> + */
> + if (certs) {
> + kfree(sev->snp_certs_data);
> + sev->snp_certs_data = certs;
> + sev->snp_certs_len = input.certs_len;
> + } else {
> + kfree(sev->snp_certs_data);
> + sev->snp_certs_data = NULL;
> + sev->snp_certs_len = 0;
> + }
> +
> + return 0;
> +
> +e_free:
> + kfree(certs);
> + return ret;
> +}
> +
> static long sev_ioctl(struct file *file, unsigned int ioctl, unsigned long arg)
> {
> void __user *argp = (void __user *)arg;
> @@ -1490,6 +1599,12 @@ static long sev_ioctl(struct file *file, unsigned int ioctl, unsigned long arg)
> case SNP_PLATFORM_STATUS:
> ret = sev_ioctl_snp_platform_status(&input);
> break;
> + case SNP_SET_EXT_CONFIG:
> + ret = sev_ioctl_snp_set_config(&input, writable);
> + break;
> + case SNP_GET_EXT_CONFIG:
> + ret = sev_ioctl_snp_get_config(&input);
> + break;

What is the intended use of `SNP_GET_EXT_CONFIG`. Yes, I get that it
returns the "EXT config" previously set via `SNP_SET_EXT_CONFIG`. But
presumably the caller can keep track of what it's previously passed to
`SNP_SET_EXT_CONFIG`. Does it really need to call into the kernel to
get these certs?

> default:
> ret = -EINVAL;
> goto out;
> diff --git a/drivers/crypto/ccp/sev-dev.h b/drivers/crypto/ccp/sev-dev.h
> index fe5d7a3ebace..d2fe1706311a 100644
> --- a/drivers/crypto/ccp/sev-dev.h
> +++ b/drivers/crypto/ccp/sev-dev.h
> @@ -66,6 +66,9 @@ struct sev_device {
>
> bool snp_inited;
> struct snp_host_map snp_host_map[MAX_SNP_HOST_MAP_BUFS];
> + void *snp_certs_data;
> + u32 snp_certs_len;
> + struct sev_user_data_snp_config snp_config;
> };
>
> int sev_dev_init(struct psp_device *psp);
> diff --git a/include/uapi/linux/psp-sev.h b/include/uapi/linux/psp-sev.h
> index ffd60e8b0a31..60e7a8d1a18e 100644
> --- a/include/uapi/linux/psp-sev.h
> +++ b/include/uapi/linux/psp-sev.h
> @@ -29,6 +29,8 @@ enum {
> SEV_GET_ID, /* This command is deprecated, use SEV_GET_ID2 */
> SEV_GET_ID2,
> SNP_PLATFORM_STATUS,
> + SNP_SET_EXT_CONFIG,
> + SNP_GET_EXT_CONFIG,
>
> SEV_MAX,
> };
> @@ -190,6 +192,21 @@ struct sev_user_data_snp_config {
> __u8 rsvd[52];
> } __packed;
>
> +/**
> + * struct sev_data_snp_ext_config - system wide configuration value for SNP.
> + *
> + * @config_address: address of the struct sev_user_data_snp_config or 0 when
> + * reported_tcb does not need to be updated.
> + * @certs_address: address of extended guest request certificate chain or
> + * 0 when previous certificate should be removed on SNP_SET_EXT_CONFIG.
> + * @certs_len: length of the certs
> + */
> +struct sev_user_data_ext_snp_config {
> + __u64 config_address; /* In */
> + __u64 certs_address; /* In */
> + __u32 certs_len; /* In */
> +};
> +
> /**
> * struct sev_issue_cmd - SEV ioctl parameters
> *
> --
> 2.17.1
>