Re: [PATCH RFC v8 27/56] crypto: ccp: Add the SNP_{SET,GET}_EXT_CONFIG command

[Zhi Wang <zhi.wang.linux@gmail.com>]

On Wed, 22 Feb 2023 16:43:54 -0600
"Kalra, Ashish" <ashish.kalra@amd.com> wrote:

> On 2/22/2023 6:32 AM, Zhi Wang wrote:
> > On Mon, 20 Feb 2023 12:38:18 -0600
> > Michael Roth <michael.roth@amd.com> wrote:
> > 
> >> From: Brijesh Singh <brijesh.singh@amd.com>
> >>
> >> 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>
> >> Signed-off-by: Ashish Kalra <ashish.kalra@amd.com>
> >> Signed-off-by: Michael Roth <michael.roth@amd.com>
> >> ---
> >>   Documentation/virt/coco/sev-guest.rst |  27 ++++++
> >>   drivers/crypto/ccp/sev-dev.c          | 123 ++++++++++++++++++++++++++
> >>   drivers/crypto/ccp/sev-dev.h          |   4 +
> >>   include/uapi/linux/psp-sev.h          |  17 ++++
> >>   4 files changed, 171 insertions(+)
> >>
> >> diff --git a/Documentation/virt/coco/sev-guest.rst b/Documentation/virt/coco/sev-guest.rst
> >> index 11ea67c944df..6cad4226c348 100644
> >> --- a/Documentation/virt/coco/sev-guest.rst
> >> +++ b/Documentation/virt/coco/sev-guest.rst
> >> @@ -145,6 +145,33 @@ 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.
> >>   
> >> +2.5 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 the previous certificate blob will deleted.
> >> +For more information on the certificate blob layout, see the GHCB spec
> >> +(extended guest request message).
> >> +
> >> +2.6 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_GET_EXT_CONFIG is used to query the system-wide configuration set
> >> +through the SNP_SET_EXT_CONFIG.
> >> +
> >>   3. SEV-SNP CPUID Enforcement
> >>   ============================
> >>   
> >> diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c
> >> index 65e13a562f3b..b56b00ca2cd4 100644
> >> --- a/drivers/crypto/ccp/sev-dev.c
> >> +++ b/drivers/crypto/ccp/sev-dev.c
> >> @@ -1481,6 +1481,10 @@ static int __sev_snp_shutdown_locked(int *error)
> >>   	data.length = sizeof(data);
> >>   	data.iommu_snp_shutdown = 1;
> >>   
> >> +	/* Free the memory used for caching the certificate data */
> >> +	kfree(sev->snp_certs_data);
> >> +	sev->snp_certs_data = NULL;
> >> +
> >>   	wbinvd_on_all_cpus();
> >>   
> >>   retry:
> >> @@ -1793,6 +1797,118 @@ 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_initialized || !argp->data)
> >> +		return -EINVAL;
> >> +
> >> +	memset(&input, 0, sizeof(input));
> >> +
> >> +	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;
> >> +
> >> +			ret = -ENOSR;
> >> +			goto e_done;
> >> +		}
> >> +
> > 
> > What about if input.certs_len > sev->snp_certs_len? Is it possbile for the
> > userspace to know the length of data in the buffer? (I guess it might be able
> > to know the certs len through the blob data, but a comment here would be nice)
> > 
> 
> If userspace provides an input buffer/length smaller then snp_certs_len, 
> then the above returns the "required" certs length back to userspace.
> 
> And what is the issue if input.certs_len > sev->snp_certs_len, the 
> buffer returned back to userspace is sev->snp_certs_len as below.
> 

My point is: How can the userspace know the length of return data is shorter
than input.certs_len when input.certs_len > sev->snp_serts_len? as the length
is only returned when input.certs_len < sev->snp_certs_len.

> Thanks,
> Ashish
> 
> >> +		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_initialized || !argp->data)
> >> +		return -EINVAL;
> >> +
> >> +	if (!writable)
> >> +		return -EPERM;
> >> +
> >> +	memset(&input, 0, sizeof(input));
> >> +
> >> +	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);
> >> +		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) {
> >> +		memset(&config, 0, sizeof(config));
> >> +		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.
> >> +	 */
> >> +	mutex_lock(&sev->snp_certs_lock);
> >> +	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;
> >> +	}
> >> +	mutex_unlock(&sev->snp_certs_lock);
> >> +
> >> +	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;
> >> @@ -1847,6 +1963,12 @@ 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;
> >>   	default:
> >>   		ret = -EINVAL;
> >>   		goto out;
> >> @@ -1962,6 +2084,7 @@ int sev_dev_init(struct psp_device *psp)
> >>   		goto e_sev;
> >>   
> >>   	sev->cmd_buf_backup = (uint8_t *)sev->cmd_buf + PAGE_SIZE;
> >> +	mutex_init(&sev->snp_certs_lock);
> >>   
> >>   	psp->sev_data = sev;
> >>   
> >> diff --git a/drivers/crypto/ccp/sev-dev.h b/drivers/crypto/ccp/sev-dev.h
> >> index 19d79f9d4212..41d5353d5bab 100644
> >> --- a/drivers/crypto/ccp/sev-dev.h
> >> +++ b/drivers/crypto/ccp/sev-dev.h
> >> @@ -66,6 +66,10 @@ struct sev_device {
> >>   
> >>   	bool snp_initialized;
> >>   	struct snp_host_map snp_host_map[MAX_SNP_HOST_MAP_BUFS];
> >> +	void *snp_certs_data;
> >> +	u32 snp_certs_len;
> >> +	struct mutex snp_certs_lock;
> >> +	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 5adfaea7df97..c20d37586d21 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,
> >>   };
> >> @@ -192,6 +194,21 @@ struct sev_user_data_snp_config {
> >>   	__u8 rsvd1[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
> >>    *
> >