Re: [PATCH RFC v8 27/56] crypto: ccp: Add the SNP_{SET,GET}_EXT_CONFIG command
From: Tom Lendacky
Date: Thu Feb 23 2023 - 09:19:55 EST
On 2/23/23 00:38, Zhi Wang wrote:
On Wed, 22 Feb 2023 16:43:54 -0600
"Kalra, Ashish" <ashish.kalra@xxxxxxx> wrote:
On 2/22/2023 6:32 AM, Zhi Wang wrote:
On Mon, 20 Feb 2023 12:38:18 -0600
Michael Roth <michael.roth@xxxxxxx> wrote:
From: Brijesh Singh <brijesh.singh@xxxxxxx>
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@xxxxxxx>
Signed-off-by: Ashish Kalra <ashish.kalra@xxxxxxx>
Signed-off-by: Michael Roth <michael.roth@xxxxxxx>
---
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.
The returned data has a defined format that can be used to calculate the
overall length.
Thanks,
Tom
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
*