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

[Marc Orr]

On Fri, Aug 20, 2021 at 9:00 AM Brijesh Singh <brijesh.singh@xxxxxxx> 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@xxxxxxx>
> ---
>  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.

> +       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
>