Re: [PATCH v3 3/4] crypto: ccp: Add support to enable CipherTextHiding on SNP_INIT_EX

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

On 4/21/25 19:25, Ashish Kalra wrote:
> From: Ashish Kalra <ashish.kalra@amd.com>
> 
> Ciphertext hiding needs to be enabled on SNP_INIT_EX.
> 
> Add two new arguments to sev_platform_init_args to allow KVM
> module to specify during SNP initialization if CipherTextHiding
> feature is to be enabled and the maximum ASID usable for an
> SEV-SNP guest when CipherTextHiding feature is enabled.
> 
> Add new API interface to indicate if SEV-SNP CipherTextHiding
> feature is supported and enabled in the Platform/BIOS.
> 
> Signed-off-by: Ashish Kalra <ashish.kalra@amd.com>
> ---
>  drivers/crypto/ccp/sev-dev.c | 31 ++++++++++++++++++++++++++++---
>  include/linux/psp-sev.h      | 18 ++++++++++++++++--
>  2 files changed, 44 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c
> index f4f8a8905115..ca4b156598de 100644
> --- a/drivers/crypto/ccp/sev-dev.c
> +++ b/drivers/crypto/ccp/sev-dev.c
> @@ -1073,6 +1073,25 @@ static void snp_set_hsave_pa(void *arg)
>  	wrmsrq(MSR_VM_HSAVE_PA, 0);
>  }
>  
> +bool is_sev_snp_ciphertext_hiding_supported(void)

sev_is_snp_ciphertext_hiding_supported

> +{
> +	struct psp_device *psp = psp_master;
> +	struct sev_device *sev;
> +
> +	sev = psp->sev_data;
> +
> +	/*
> +	 * Check if CipherTextHiding feature is supported and enabled
> +	 * in the Platform/BIOS.

I think this should be expanded a bit to indicate why both the feature
info and the platform status fields have to be checked.

> +	 */
> +	if ((sev->feat_info.ecx & SNP_CIPHER_TEXT_HIDING_SUPPORTED) &&
> +	    sev->snp_plat_status.ciphertext_hiding_cap)
> +		return true;
> +
> +	return false;

And then just make this:

  return (sev->feat_info.ecx & SNP_CIPHER_TEXT_HIDING_SUPPORTED) &&
	 sev->snp_plat_status.ciphertext_hiding_cap);

> +}
> +EXPORT_SYMBOL_GPL(is_sev_snp_ciphertext_hiding_supported);
> +
>  static void snp_get_platform_data(void)
>  {
>  	struct sev_device *sev = psp_master->sev_data;
> @@ -1147,7 +1166,7 @@ static int snp_filter_reserved_mem_regions(struct resource *rs, void *arg)
>  	return 0;
>  }
>  
> -static int __sev_snp_init_locked(int *error)
> +static int __sev_snp_init_locked(int *error, bool cipher_text_hiding_en, unsigned int snp_max_snp_asid)
>  {
>  	struct psp_device *psp = psp_master;
>  	struct sev_data_snp_init_ex data;
> @@ -1208,6 +1227,12 @@ static int __sev_snp_init_locked(int *error)
>  		}
>  
>  		memset(&data, 0, sizeof(data));
> +
> +		if (cipher_text_hiding_en) {
> +			data.ciphertext_hiding_en = 1;
> +			data.max_snp_asid = snp_max_snp_asid;
> +		}
> +
>  		data.init_rmp = 1;
>  		data.list_paddr_en = 1;
>  		data.list_paddr = __psp_pa(snp_range_list);
> @@ -1392,7 +1417,7 @@ static int _sev_platform_init_locked(struct sev_platform_init_args *args)
>  	if (sev->state == SEV_STATE_INIT)
>  		return 0;
>  
> -	rc = __sev_snp_init_locked(&args->error);
> +	rc = __sev_snp_init_locked(&args->error, args->cipher_text_hiding_en, args->snp_max_snp_asid);
>  	if (rc && rc != -ENODEV)
>  		return rc;
>  
> @@ -1475,7 +1500,7 @@ static int snp_move_to_init_state(struct sev_issue_cmd *argp, bool *shutdown_req
>  {
>  	int error, rc;
>  
> -	rc = __sev_snp_init_locked(&error);
> +	rc = __sev_snp_init_locked(&error, false, 0);
>  	if (rc) {
>  		argp->error = SEV_RET_INVALID_PLATFORM_STATE;
>  		return rc;
> diff --git a/include/linux/psp-sev.h b/include/linux/psp-sev.h
> index 0149d4a6aceb..af45e3e372f5 100644
> --- a/include/linux/psp-sev.h
> +++ b/include/linux/psp-sev.h
> @@ -746,10 +746,13 @@ struct sev_data_snp_guest_request {
>  struct sev_data_snp_init_ex {
>  	u32 init_rmp:1;
>  	u32 list_paddr_en:1;
> -	u32 rsvd:30;
> +	u32 rapl_dis:1;
> +	u32 ciphertext_hiding_en:1;
> +	u32 rsvd:28;
>  	u32 rsvd1;
>  	u64 list_paddr;
> -	u8  rsvd2[48];
> +	u16 max_snp_asid;
> +	u8  rsvd2[46];
>  } __packed;
>  
>  /**
> @@ -798,10 +801,16 @@ struct sev_data_snp_shutdown_ex {
>   * @probe: True if this is being called as part of CCP module probe, which
>   *  will defer SEV_INIT/SEV_INIT_EX firmware initialization until needed
>   *  unless psp_init_on_probe module param is set
> + *  @cipher_text_hiding_en: True if SEV-SNP CipherTextHiding support is

s/is/is to be/

Thanks,
Tom

> + *  enabled
> + *  @snp_max_snp_asid: maximum ASID usable for SEV-SNP guest if
> + *  CipherTextHiding is enabled
>   */
>  struct sev_platform_init_args {
>  	int error;
>  	bool probe;
> +	bool cipher_text_hiding_en;
> +	unsigned int snp_max_snp_asid;
>  };
>  
>  /**
> @@ -841,6 +850,8 @@ struct snp_feature_info {
>  	u32 edx;
>  } __packed;
>  
> +#define SNP_CIPHER_TEXT_HIDING_SUPPORTED	BIT(3)
> +
>  #ifdef CONFIG_CRYPTO_DEV_SP_PSP
>  
>  /**
> @@ -984,6 +995,7 @@ 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 is_sev_snp_ciphertext_hiding_supported(void);
>  
>  #else	/* !CONFIG_CRYPTO_DEV_SP_PSP */
>  
> @@ -1020,6 +1032,8 @@ static inline void snp_free_firmware_page(void *addr) { }
>  
>  static inline void sev_platform_shutdown(void) { }
>  
> +static inline bool is_sev_snp_ciphertext_hiding_supported(void) { return FALSE; }
> +
>  #endif	/* CONFIG_CRYPTO_DEV_SP_PSP */
>  
>  #endif	/* __PSP_SEV_H__ */