Re: [PATCH Part2 v5 18/45] crypto: ccp: Provide APIs to query extended attestation report

Dov Murik
2021-09-12T07:47:42Z

On 10/09/2021 6:30, Marc Orr wrote:
> On Fri, Aug 20, 2021 at 9:00 AM Brijesh Singh <brijesh.singh@amd.com> wrote:
>>
>> Version 2 of the GHCB specification defines VMGEXIT that is used to get
>> the extended attestation report. The extended attestation report includes
>> the certificate blobs provided through the SNP_SET_EXT_CONFIG.
>>
>> The snp_guest_ext_guest_request() will be used by the hypervisor to get
>> the extended attestation report. See the GHCB specification for more
>> details.
>>
>> Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
>> ---
>> drivers/crypto/ccp/sev-dev.c | 43 ++++++++++++++++++++++++++++++++++++
>> include/linux/psp-sev.h | 24 ++++++++++++++++++++
>> 2 files changed, 67 insertions(+)
>>
>> diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c
>> index 9ba194acbe85..e2650c3d0d0a 100644
>> --- a/drivers/crypto/ccp/sev-dev.c
>> +++ b/drivers/crypto/ccp/sev-dev.c
>> @@ -22,6 +22,7 @@
>> #include <linux/firmware.h>
>> #include <linux/gfp.h>
>> #include <linux/cpufeature.h>
>> +#include <linux/sev-guest.h>
>>
>> #include <asm/smp.h>
>>
>> @@ -1677,6 +1678,48 @@ int snp_guest_dbg_decrypt(struct sev_data_snp_dbg *data, int *error)
>> }
>> EXPORT_SYMBOL_GPL(snp_guest_dbg_decrypt);
>>
>> +int snp_guest_ext_guest_request(struct sev_data_snp_guest_request *data,
>> + unsigned long vaddr, unsigned long *npages, unsigned long *fw_err)
>> +{
>> + unsigned long expected_npages;
>> + struct sev_device *sev;
>> + int rc;
>> +
>> + if (!psp_master || !psp_master->sev_data)
>> + return -ENODEV;
>> +
>> + sev = psp_master->sev_data;
>> +
>> + if (!sev->snp_inited)
>> + return -EINVAL;
>> +
>> + /*
>> + * Check if there is enough space to copy the certificate chain. Otherwise
>> + * return ERROR code defined in the GHCB specification.
>> + */
>> + expected_npages = sev->snp_certs_len >> PAGE_SHIFT;
>
> Is this calculation for `expected_npages` correct? Assume that
> `sev->snp_certs_len` is less than a page (e.g., 2000). Then, this
> calculation will return `0` for `expected_npages`, rather than round
> up to 1.
>

In patch 17 in sev_ioctl_snp_set_config there's a check that certs_len
is aligned to PAGE_SIZE (and this value is later in that function assigned
to sev->snp_certs_len):

+ /* Copy the certs from userspace */
+ if (input.certs_address) {
+ if (!input.certs_len || !IS_ALIGNED(input.certs_len, PAGE_SIZE))
+ return -EINVAL;

but I agree that rounding up (DIV_ROUND_UP) or asserting that
sev->snp_certs_len is aligned to PAGE_SIZE (and non-zero) makes
sense here.

-Dov

>> + if (*npages < expected_npages) {
>> + *npages = expected_npages;
>> + *fw_err = SNP_GUEST_REQ_INVALID_LEN;
>> + return -EINVAL;
>> + }
>> +
>> + rc = sev_do_cmd(SEV_CMD_SNP_GUEST_REQUEST, data, (int *)&fw_err);
>> + if (rc)
>> + return rc;
>> +
>> + /* Copy the certificate blob */
>> + if (sev->snp_certs_data) {
>> + *npages = expected_npages;
>> + memcpy((void *)vaddr, sev->snp_certs_data, *npages << PAGE_SHIFT);
>> + } else {
>> + *npages = 0;
>> + }
>> +
>> + return rc;
>> +}
>> +EXPORT_SYMBOL_GPL(snp_guest_ext_guest_request);
>> +
>> static void sev_exit(struct kref *ref)
>> {
>> misc_deregister(&misc_dev->misc);
>> diff --git a/include/linux/psp-sev.h b/include/linux/psp-sev.h
>> index 00bd684dc094..ea94ce4d834a 100644
>> --- a/include/linux/psp-sev.h
>> +++ b/include/linux/psp-sev.h
>> @@ -924,6 +924,23 @@ void *psp_copy_user_blob(u64 uaddr, u32 len);
>> void *snp_alloc_firmware_page(gfp_t mask);
>> void snp_free_firmware_page(void *addr);
>>
>> +/**
>> + * snp_guest_ext_guest_request - perform the SNP extended guest request command
>> + * defined in the GHCB specification.
>> + *
>> + * @data: the input guest request structure
>> + * @vaddr: address where the certificate blob need to be copied.
>> + * @npages: number of pages for the certificate blob.
>> + * If the specified page count is less than the certificate blob size, then the
>> + * required page count is returned with error code defined in the GHCB spec.
>> + * If the specified page count is more than the certificate blob size, then
>> + * page count is updated to reflect the amount of valid data copied in the
>> + * vaddr.
>> + */
>> +int snp_guest_ext_guest_request(struct sev_data_snp_guest_request *data,
>> + unsigned long vaddr, unsigned long *npages,
>> + unsigned long *error);
>> +
>> #else /* !CONFIG_CRYPTO_DEV_SP_PSP */
>>
>> static inline int
>> @@ -971,6 +988,13 @@ static inline void *snp_alloc_firmware_page(gfp_t mask)
>>
>> static inline void snp_free_firmware_page(void *addr) { }
>>
>> +static inline int snp_guest_ext_guest_request(struct sev_data_snp_guest_request *data,
>> + unsigned long vaddr, unsigned long *n,
>> + unsigned long *error)
>> +{
>> + return -ENODEV;
>> +}
>> +
>> #endif /* CONFIG_CRYPTO_DEV_SP_PSP */
>>
>> #endif /* __PSP_SEV_H__ */
>> --
>> 2.17.1
>>