linux-kernel - Re: [PATCH v7 01/10] KVM: SEV: Disable SEV-SNP support on initialization failure

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Message-ID: <593571c4-39c5-4647-82f2-98094ec9f437@oracle.com>
Date: Mon, 24 Feb 2025 19:01:07 +0000
From: Liam Merwick <liam.merwick@...cle.com>
To: "Pratik R. Sampat" <prsampat@....com>, linux-kernel@...r.kernel.org,
        x86@...nel.org, kvm@...r.kernel.org, linux-crypto@...r.kernel.org,
        linux-kselftest@...r.kernel.org
Cc: seanjc@...gle.com, pbonzini@...hat.com, thomas.lendacky@....com,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, shuah@...nel.org, pgonda@...gle.com,
        ashish.kalra@....com, nikunj@....com, pankaj.gupta@....com,
        michael.roth@....com, sraithal@....com, liam.merwick@...cle.com
Subject: Re: [PATCH v7 01/10] KVM: SEV: Disable SEV-SNP support on
 initialization failure



On 21/02/2025 21:01, Pratik R. Sampat wrote:
> During platform init, SNP initialization may fail for several reasons,
> such as firmware command failures and incompatible versions. However,
> the KVM capability may continue to advertise support for it. Export this
> information to KVM and withdraw SEV-SNP support if has not been
> successfully initialized.
> 
> Fixes: 1dfe571c12cf ("KVM: SEV: Add initial SEV-SNP support")
> Suggested-by: Sean Christopherson <seanjc@...gle.com>
> Signed-off-by: Pratik R. Sampat <prsampat@....com>
> ---
> v6..v7:
> 
> * Replace FW version check with sev->snp_initialized (Sean)
> ---
>   arch/x86/kvm/svm/sev.c       | 4 +++-
>   drivers/crypto/ccp/sev-dev.c | 8 ++++++++
>   include/linux/psp-sev.h      | 3 +++
>   3 files changed, 14 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index 0dbb25442ec1..87b5d63a5817 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -3050,7 +3050,9 @@ void __init sev_hardware_setup(void)
>   	sev_es_asid_count = min_sev_asid - 1;
>   	WARN_ON_ONCE(misc_cg_set_capacity(MISC_CG_RES_SEV_ES, sev_es_asid_count));
>   	sev_es_supported = true;
> -	sev_snp_supported = sev_snp_enabled && cc_platform_has(CC_ATTR_HOST_SEV_SNP);
> +	sev_snp_supported = (sev_snp_enabled &&
> +			    cc_platform_has(CC_ATTR_HOST_SEV_SNP) &&
> +			    snp_initialized());
>   
>   out:
>   	if (boot_cpu_has(X86_FEATURE_SEV))
> diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c
> index 2e87ca0e292a..8d2cf8552bc2 100644
> --- a/drivers/crypto/ccp/sev-dev.c
> +++ b/drivers/crypto/ccp/sev-dev.c
> @@ -1352,6 +1352,14 @@ int sev_platform_init(struct sev_platform_init_args *args)
>   }
>   EXPORT_SYMBOL_GPL(sev_platform_init);
>   
> +bool snp_initialized(void)
> +{
> +	struct sev_device *sev = psp_master->sev_data;


Should check psp_master isn't NULL before accessing just in case
(particularly for future potential callers).

(e.g. see ccb88e9549e7 ("crypto: ccp - Fix null pointer dereference in 
__sev_platform_shutdown_locked")




> +
> +	return sev->snp_initialized;
> +}
> +EXPORT_SYMBOL_GPL(snp_initialized);
> +
>   static int __sev_platform_shutdown_locked(int *error)
>   {
>   	struct psp_device *psp = psp_master;
> diff --git a/include/linux/psp-sev.h b/include/linux/psp-sev.h
> index f3cad182d4ef..d34068c87a28 100644
> --- a/include/linux/psp-sev.h
> +++ b/include/linux/psp-sev.h
> @@ -954,6 +954,7 @@ int sev_do_cmd(int cmd, void *data, int *psp_ret);
>   void *psp_copy_user_blob(u64 uaddr, u32 len);
>   void *snp_alloc_firmware_page(gfp_t mask);
>   void snp_free_firmware_page(void *addr);
> +bool snp_initialized(void);
>   
>   #else	/* !CONFIG_CRYPTO_DEV_SP_PSP */
>   
> @@ -988,6 +989,8 @@ static inline void *snp_alloc_firmware_page(gfp_t mask)
>   
>   static inline void snp_free_firmware_page(void *addr) { }
>   
> +static inline bool snp_initialized(void) { return false; }
> +
>   #endif	/* CONFIG_CRYPTO_DEV_SP_PSP */
>   
>   #endif	/* __PSP_SEV_H__ */