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

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Message-ID: <f66c47d0-d111-45a8-8cf5-bd4577bbe6e5@amd.com>
Date: Tue, 25 Feb 2025 10:50:13 -0600
From: "Pratik R. Sampat" <prsampat@....com>
To: Liam Merwick <liam.merwick@...cle.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>
Subject: Re: [PATCH v7 01/10] KVM: SEV: Disable SEV-SNP support on
 initialization failure

Hi Liam,

Thanks for review!

On 2/24/2025 1:01 PM, Liam Merwick wrote:
> 
> 
> 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")
> 

Thanks for pointing this out, if I end up using this interface, I'll put
the NULL check in.

Thanks!
Pratik
> 
> 
> 
>> +
>> +    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__ */
>