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Message-ID: <e59803e9-017a-4257-ac9c-7bdafbc624ff@amd.com>
Date: Thu, 5 Jun 2025 16:32:57 +1000
From: Alexey Kardashevskiy <aik@....com>
To: Ashish Kalra <Ashish.Kalra@....com>, seanjc@...gle.com,
pbonzini@...hat.com, tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
dave.hansen@...ux.intel.com, hpa@...or.com, herbert@...dor.apana.org.au
Cc: x86@...nel.org, john.allen@....com, davem@...emloft.net,
thomas.lendacky@....com, michael.roth@....com, kvm@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-crypto@...r.kernel.org
Subject: Re: [PATCH v4 3/5] crypto: ccp: Add support to enable
CipherTextHiding on SNP_INIT_EX
On 20/5/25 09:57, Ashish Kalra wrote:
> From: Ashish Kalra <ashish.kalra@....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@....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,
> +
> #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__ */
--
Alexey
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