linux-kernel - Re: [PATCH v3 2/4] crypto: ccp: Add support for SNP_FEATURE

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Message-ID: <7da931d3e045aad6349879c16db9a8bf17aa0d60.camel@gmail.com>
Date: Thu, 24 Apr 2025 16:38:58 +0200
From: Francesco Lavra <francescolavra.fl@...il.com>
To: ashish.kalra@....com
Cc: bp@...en8.de, dave.hansen@...ux.intel.com, davem@...emloft.net, 
 herbert@...dor.apana.org.au, hpa@...or.com, john.allen@....com, 
 kvm@...r.kernel.org, linux-crypto@...r.kernel.org,
 linux-kernel@...r.kernel.org,  michael.roth@....com, mingo@...hat.com,
 pbonzini@...hat.com, seanjc@...gle.com,  tglx@...utronix.de,
 thomas.lendacky@....com, x86@...nel.org
Subject: Re: [PATCH v3 2/4] crypto: ccp: Add support for SNP_FEATURE_INFO
 command

On 2025-04-22 at 0:24, Ashish Kalra wrote:
> diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-
> dev.c
> index b08db412f752..f4f8a8905115 100644
> --- a/drivers/crypto/ccp/sev-dev.c
> +++ b/drivers/crypto/ccp/sev-dev.c
> @@ -232,6 +232,7 @@ static int sev_cmd_buffer_len(int cmd)
>  	case SEV_CMD_SNP_GUEST_REQUEST:		return
> sizeof(struct sev_data_snp_guest_request);
>  	case SEV_CMD_SNP_CONFIG:		return sizeof(struct
> sev_user_data_snp_config);
>  	case SEV_CMD_SNP_COMMIT:		return sizeof(struct
> sev_data_snp_commit);
> +	case SEV_CMD_SNP_FEATURE_INFO:		return sizeof(struct
> snp_feature_info);

This function is supposed to return the size of the command buffer, so
for this command it should return sizeof(struct
sev_data_snp_feature_info).

>  	default:				return 0;
>  	}
>  
> @@ -1072,6 +1073,50 @@ static void snp_set_hsave_pa(void *arg)
>  	wrmsrq(MSR_VM_HSAVE_PA, 0);
>  }
>  
> +static void snp_get_platform_data(void)
> +{
> +	struct sev_device *sev = psp_master->sev_data;
> +	struct sev_data_snp_feature_info snp_feat_info;
> +	struct snp_feature_info *feat_info;
> +	struct sev_data_snp_addr buf;
> +	int error = 0, rc;
> +
> +	if (!cc_platform_has(CC_ATTR_HOST_SEV_SNP))
> +		return;
> +
> +	/*
> +	 * The output buffer must be firmware page if SEV-SNP is
> +	 * initialized.
> +	 */
> +	if (sev->snp_initialized)
> +		return;
> +
> +	buf.address = __psp_pa(&sev->snp_plat_status);
> +	rc = __sev_do_cmd_locked(SEV_CMD_SNP_PLATFORM_STATUS, &buf,
> &error);
> +
> +	/*
> +	 * Do feature discovery of the currently loaded firmware,
> +	 * and cache feature information from CPUID 0x8000_0024,
> +	 * sub-function 0.
> +	 */
> +	if (!rc && sev->snp_plat_status.feature_info) {
> +		/*
> +		 * Use dynamically allocated structure for the
> SNP_FEATURE_INFO
> +		 * command to handle any alignment and page boundary
> check
> +		 * requirements.
> +		 */
> +		feat_info = kzalloc(sizeof(*feat_info), GFP_KERNEL);

The SEV firmware requires the supplied memory range to not cross a page
boundary, but kzalloc() does not guarantee that the allocated memory
fits this requirement. You need to allocate a larger chunk of memory (2
* sizeof(*feat_info) will be enough), and possibly set
feature_info_paddr to an offset from the start of the allocated memory.