Re: [PATCH v5 4/7] crypto: ccp - Introduce new API interface to indicate SEV-SNP Ciphertext hiding feature

[Tom Lendacky <thomas.lendacky@amd.com>]

On 7/1/25 15:15, Ashish Kalra wrote:
> From: Ashish Kalra <ashish.kalra@amd.com>
> 
> Implement a new API interface that indicates both the support for the
> SEV-SNP Ciphertext Hiding feature by the SEV firmware and whether this
> feature is enabled in the platform BIOS.

The API is a single result about support, so how about something like:

  Implement an API that checks overall feature support for SEV-SNP
  ciphertext hiding.

  The API verifies both the SEV firmware's support for the feature and
  its enablement in the platform's BIOS.

Thanks,
Tom

> 
> Signed-off-by: Ashish Kalra <ashish.kalra@amd.com>
> ---
>  drivers/crypto/ccp/sev-dev.c | 21 +++++++++++++++++++++
>  include/linux/psp-sev.h      |  5 +++++
>  2 files changed, 26 insertions(+)
> 
> diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c
> index d1517a91a27d..3f2bbba93617 100644
> --- a/drivers/crypto/ccp/sev-dev.c
> +++ b/drivers/crypto/ccp/sev-dev.c
> @@ -1074,6 +1074,27 @@ static void snp_set_hsave_pa(void *arg)
>  	wrmsrq(MSR_VM_HSAVE_PA, 0);
>  }
>  
> +bool sev_is_snp_ciphertext_hiding_supported(void)
> +{
> +	struct psp_device *psp = psp_master;
> +	struct sev_device *sev;
> +
> +	if (!psp || !psp->sev_data)
> +		return false;
> +
> +	sev = psp->sev_data;
> +
> +	/*
> +	 * Feature information indicates if CipherTextHiding feature is
> +	 * supported by the SEV firmware and additionally platform status
> +	 * indicates if CipherTextHiding feature is enabled in the
> +	 * Platform BIOS.
> +	 */
> +	return ((sev->snp_feat_info_0.ecx & SNP_CIPHER_TEXT_HIDING_SUPPORTED) &&
> +		 sev->snp_plat_status.ciphertext_hiding_cap);
> +}
> +EXPORT_SYMBOL_GPL(sev_is_snp_ciphertext_hiding_supported);
> +
>  static int snp_get_platform_data(struct sev_device *sev, int *error)
>  {
>  	struct sev_data_snp_feature_info snp_feat_info;
> diff --git a/include/linux/psp-sev.h b/include/linux/psp-sev.h
> index 935547c26985..ca19fddfcd4d 100644
> --- a/include/linux/psp-sev.h
> +++ b/include/linux/psp-sev.h
> @@ -843,6 +843,8 @@ struct snp_feature_info {
>  	u32 edx;
>  } __packed;
>  
> +#define SNP_CIPHER_TEXT_HIDING_SUPPORTED	BIT(3)
> +
>  #ifdef CONFIG_CRYPTO_DEV_SP_PSP
>  
>  /**
> @@ -986,6 +988,7 @@ void *psp_copy_user_blob(u64 uaddr, u32 len);
>  void *snp_alloc_firmware_page(gfp_t mask);
>  void snp_free_firmware_page(void *addr);
>  void sev_platform_shutdown(void);
> +bool sev_is_snp_ciphertext_hiding_supported(void);
>  
>  #else	/* !CONFIG_CRYPTO_DEV_SP_PSP */
>  
> @@ -1022,6 +1025,8 @@ static inline void snp_free_firmware_page(void *addr) { }
>  
>  static inline void sev_platform_shutdown(void) { }
>  
> +static inline bool sev_is_snp_ciphertext_hiding_supported(void) { return false; }
> +
>  #endif	/* CONFIG_CRYPTO_DEV_SP_PSP */
>  
>  #endif	/* __PSP_SEV_H__ */