Re: [PATCH RFC v8 52/56] ccp: Add support to decrypt the page

[Zhi Wang]

On Mon, 20 Feb 2023 12:38:43 -0600
Michael Roth <michael.roth@xxxxxxx> wrote:

> From: Brijesh Singh <brijesh.singh@xxxxxxx>
> 
> Add support to decrypt guest encrypted memory. These API interfaces can
> be used for example to dump VMCBs on SNP guest exit.
> 

What kinds of check will be applied from firmware when VMM decrypts this
page? I suppose there has to be kinda mechanism to prevent VMM to decrypt
any page in the guest. It would be nice to have some introduction about
it in the comments.

> Signed-off-by: Brijesh Singh <brijesh.singh@xxxxxxx>
> Signed-off-by: Ashish Kalra <ashish.kalra@xxxxxxx>
> [mdr: minor commit fixups]
> Signed-off-by: Michael Roth <michael.roth@xxxxxxx>
> ---
>  drivers/crypto/ccp/sev-dev.c | 32 ++++++++++++++++++++++++++++++++
>  include/linux/psp-sev.h      | 22 ++++++++++++++++++++--
>  2 files changed, 52 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c
> index e65563bc8298..bf5167b2acfc 100644
> --- a/drivers/crypto/ccp/sev-dev.c
> +++ b/drivers/crypto/ccp/sev-dev.c
> @@ -2017,6 +2017,38 @@ int sev_guest_df_flush(int *error)
>  }
>  EXPORT_SYMBOL_GPL(sev_guest_df_flush);
>  
> +int snp_guest_dbg_decrypt_page(u64 gctx_pfn, u64 src_pfn, u64 dst_pfn, int *error)
> +{
> +	struct sev_data_snp_dbg data = {0};
> +	struct sev_device *sev;
> +	int ret;
> +
> +	if (!psp_master || !psp_master->sev_data)
> +		return -ENODEV;
> +
> +	sev = psp_master->sev_data;
> +
> +	if (!sev->snp_initialized)
> +		return -EINVAL;
> +
> +	data.gctx_paddr = sme_me_mask | (gctx_pfn << PAGE_SHIFT);
> +	data.src_addr = sme_me_mask | (src_pfn << PAGE_SHIFT);
> +	data.dst_addr = sme_me_mask | (dst_pfn << PAGE_SHIFT);
> +
> +	/* The destination page must be in the firmware state. */
> +	if (rmp_mark_pages_firmware(data.dst_addr, 1, false))
> +		return -EIO;
> +
> +	ret = sev_do_cmd(SEV_CMD_SNP_DBG_DECRYPT, &data, error);
> +
> +	/* Restore the page state */
> +	if (snp_reclaim_pages(data.dst_addr, 1, false))
> +		ret = -EIO;
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(snp_guest_dbg_decrypt_page);
> +
>  int snp_guest_ext_guest_request(struct sev_data_snp_guest_request *data,
>  				unsigned long vaddr, unsigned long *npages, unsigned long *fw_err)
>  {
> diff --git a/include/linux/psp-sev.h b/include/linux/psp-sev.h
> index 81bafc049eca..92116e2b74fd 100644
> --- a/include/linux/psp-sev.h
> +++ b/include/linux/psp-sev.h
> @@ -710,7 +710,6 @@ struct sev_data_snp_dbg {
>  	u64 gctx_paddr;				/* In */
>  	u64 src_addr;				/* In */
>  	u64 dst_addr;				/* In */
> -	u32 len;				/* In */
>  } __packed;
>  
>  /**
> @@ -913,13 +912,27 @@ int sev_guest_decommission(struct sev_data_decommission *data, int *error);
>   * @error: SEV command return code
>   *
>   * Returns:
> + * 0 if the sev successfully processed the command
> + * -%ENODEV    if the sev device is not available
> + * -%ENOTSUPP  if the sev does not support SEV
> + * -%ETIMEDOUT if the sev command timed out
> + * -%EIO       if the sev returned a non-zero return code
> + */
> +int sev_do_cmd(int cmd, void *data, int *psp_ret);
> +
> +/**
> + * snp_guest_dbg_decrypt_page - perform SEV SNP_DBG_DECRYPT command
> + *
> + * @sev_ret: sev command return code
> + *
> + * Returns:
>   * 0 if the SEV successfully processed the command
>   * -%ENODEV    if the SEV device is not available
>   * -%ENOTSUPP  if the SEV does not support SEV
>   * -%ETIMEDOUT if the SEV command timed out
>   * -%EIO       if the SEV returned a non-zero return code
>   */
> -int sev_do_cmd(int cmd, void *data, int *psp_ret);
> +int snp_guest_dbg_decrypt_page(u64 gctx_pfn, u64 src_pfn, u64 dst_pfn, int *error);
>  
>  void *psp_copy_user_blob(u64 uaddr, u32 len);
>  void *snp_alloc_firmware_page(gfp_t mask);
> @@ -987,6 +1000,11 @@ static inline void *psp_copy_user_blob(u64 __user uaddr, u32 len) { return ERR_P
>  
>  void snp_mark_pages_offline(unsigned long pfn, unsigned int npages) {}
>  
> +static inline int snp_guest_dbg_decrypt_page(u64 gctx_pfn, u64 src_pfn, u64 dst_pfn, int *error)
> +{
> +	return -ENODEV;
> +}
> +
>  static inline void *snp_alloc_firmware_page(gfp_t mask)
>  {
>  	return NULL;