Re: [PATCH v4 3/5] crypto: ccp: Add support to enable CipherTextHiding on SNP_INIT_EX

["Kalra, Ashish" <ashish.kalra@amd.com>]

On 6/5/2025 1:32 AM, Alexey Kardashevskiy wrote:
> On 20/5/25 09:57, Ashish Kalra wrote:
>> From: Ashish Kalra <ashish.kalra@amd.com>
>>
>> Ciphertext hiding needs to be enabled on SNP_INIT_EX.
>>
>> Add new argument 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 by SEV firmware and additionally if
>> CipherTextHiding feature is enabled in the Platform BIOS.
>>
>> Signed-off-by: Ashish Kalra <ashish.kalra@amd.com>
>> ---
>>   drivers/crypto/ccp/sev-dev.c | 30 +++++++++++++++++++++++++++---
>>   include/linux/psp-sev.h      | 15 +++++++++++++--
>>   2 files changed, 40 insertions(+), 5 deletions(-)
>>
>> diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c
>> index b642f1183b8b..185668477182 100644
>> --- a/drivers/crypto/ccp/sev-dev.c
>> +++ b/drivers/crypto/ccp/sev-dev.c
>> @@ -1074,6 +1074,24 @@ 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;
>> +
>> +    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->feat_info.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_user_data_status *status, int *error)
>>   {
>>       struct sev_data_snp_feature_info snp_feat_info;
>> @@ -1167,7 +1185,7 @@ 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, unsigned int snp_max_snp_asid)
>>   {
>>       struct psp_device *psp = psp_master;
>>       struct sev_data_snp_init_ex data;
>> @@ -1228,6 +1246,12 @@ static int __sev_snp_init_locked(int *error)
>>           }
>>             memset(&data, 0, sizeof(data));
>> +
>> +        if (snp_max_snp_asid) {
>> +            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);
>> @@ -1412,7 +1436,7 @@ 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->snp_max_snp_asid);
>>       if (rc && rc != -ENODEV)
>>           return rc;
>>   @@ -1495,7 +1519,7 @@ 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, 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..66fecd0c0f88 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 +801,13 @@ 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
>> + *  @snp_max_snp_asid: maximum ASID usable for SEV-SNP guest if
>> + *  CipherTextHiding feature is to be enabled
>>    */
>>   struct sev_platform_init_args {
>>       int error;
>>       bool probe;
>> +    unsigned int snp_max_snp_asid;
>>   };
>>     /**
>> @@ -841,6 +847,8 @@ struct snp_feature_info {
>>       u32 edx;
>>   } __packed;
>>   +#define SNP_CIPHER_TEXT_HIDING_SUPPORTED    BIT(3)
> 
> SNP_FEATURE_CIPHER_TEXT_HIDING ?
> or X86_FEATURE_CIPHER_TEXT_HIDING ?
> 
> In other words, mimic X86_FEATURE_SEV which is a real CPUID bit and FEATURE_INFO mimics CPUID. Thanks,
>

I will still prefer to name it SNP_FEATURE_CIPHER_TEXT_HIDING, as the SNP FW ABI specs names it as such
and it is a SNP specific feature, prefixing X86 is confusing.

Thanks,
Ashish
 
> 
>> +
>>   #ifdef CONFIG_CRYPTO_DEV_SP_PSP
>>     /**
>> @@ -984,6 +992,7 @@ 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 */
>>   @@ -1020,6 +1029,8 @@ 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__ */
>