linux-kernel - Re: [PATCH RFC v8 27/56] crypto: ccp: Add the SNP_{SET,GET}_EXT

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Date:   Wed, 22 Feb 2023 10:50:12 -0600
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Zhi Wang <zhi.wang.linux@...il.com>,
        Michael Roth <michael.roth@....com>
Cc:     kvm@...r.kernel.org, linux-coco@...ts.linux.dev,
        linux-mm@...ck.org, linux-crypto@...r.kernel.org, x86@...nel.org,
        linux-kernel@...r.kernel.org, tglx@...utronix.de, mingo@...hat.com,
        jroedel@...e.de, hpa@...or.com, ardb@...nel.org,
        pbonzini@...hat.com, seanjc@...gle.com, vkuznets@...hat.com,
        jmattson@...gle.com, luto@...nel.org, dave.hansen@...ux.intel.com,
        slp@...hat.com, pgonda@...gle.com, peterz@...radead.org,
        srinivas.pandruvada@...ux.intel.com, rientjes@...gle.com,
        dovmurik@...ux.ibm.com, tobin@....com, bp@...en8.de,
        vbabka@...e.cz, kirill@...temov.name, ak@...ux.intel.com,
        tony.luck@...el.com, marcorr@...gle.com,
        sathyanarayanan.kuppuswamy@...ux.intel.com, alpergun@...gle.com,
        dgilbert@...hat.com, jarkko@...nel.org, ashish.kalra@....com,
        nikunj.dadhania@....com, Brijesh Singh <brijesh.singh@....com>
Subject: Re: [PATCH RFC v8 27/56] crypto: ccp: Add the
 SNP_{SET,GET}_EXT_CONFIG command

On 2/22/23 06:32, Zhi Wang wrote:
> On Mon, 20 Feb 2023 12:38:18 -0600
> Michael Roth <michael.roth@....com> wrote:
> 
>> From: Brijesh Singh <brijesh.singh@....com>
>>
>> The SEV-SNP firmware provides the SNP_CONFIG command used to set the
>> system-wide configuration value for SNP guests. The information includes
>> the TCB version string to be reported in guest attestation reports.
>>
>> Version 2 of the GHCB specification adds an NAE (SNP extended guest
>> request) that a guest can use to query the reports that include additional
>> certificates.
>>
>> In both cases, userspace provided additional data is included in the
>> attestation reports. The userspace will use the SNP_SET_EXT_CONFIG
>> command to give the certificate blob and the reported TCB version string
>> at once. Note that the specification defines certificate blob with a
>> specific GUID format; the userspace is responsible for building the
>> proper certificate blob. The ioctl treats it an opaque blob.
>>
>> While it is not defined in the spec, but let's add SNP_GET_EXT_CONFIG
>> command that can be used to obtain the data programmed through the
>> SNP_SET_EXT_CONFIG.
>>
>> Signed-off-by: Brijesh Singh <brijesh.singh@....com>
>> Signed-off-by: Ashish Kalra <ashish.kalra@....com>
>> Signed-off-by: Michael Roth <michael.roth@....com>
>> ---
>>   Documentation/virt/coco/sev-guest.rst |  27 ++++++
>>   drivers/crypto/ccp/sev-dev.c          | 123 ++++++++++++++++++++++++++
>>   drivers/crypto/ccp/sev-dev.h          |   4 +
>>   include/uapi/linux/psp-sev.h          |  17 ++++
>>   4 files changed, 171 insertions(+)
>>

>> diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c
>> index 65e13a562f3b..b56b00ca2cd4 100644
>> --- a/drivers/crypto/ccp/sev-dev.c
>> +++ b/drivers/crypto/ccp/sev-dev.c
>> @@ -1481,6 +1481,10 @@ static int __sev_snp_shutdown_locked(int *error)
>>   	data.length = sizeof(data);
>>   	data.iommu_snp_shutdown = 1;
>>   
>> +	/* Free the memory used for caching the certificate data */
>> +	kfree(sev->snp_certs_data);
>> +	sev->snp_certs_data = NULL;
>> +
>>   	wbinvd_on_all_cpus();
>>   
>>   retry:
>> @@ -1793,6 +1797,118 @@ static int sev_ioctl_snp_platform_status(struct sev_issue_cmd *argp)
>>   	return ret;
>>   }
>>   
>> +static int sev_ioctl_snp_get_config(struct sev_issue_cmd *argp)
>> +{
>> +	struct sev_device *sev = psp_master->sev_data;
>> +	struct sev_user_data_ext_snp_config input;
>> +	int ret;
>> +
>> +	if (!sev->snp_initialized || !argp->data)
>> +		return -EINVAL;
>> +
>> +	memset(&input, 0, sizeof(input));
>> +
>> +	if (copy_from_user(&input, (void __user *)argp->data, sizeof(input)))
>> +		return -EFAULT;
>> +
>> +	/* Copy the TCB version programmed through the SET_CONFIG to userspace */
>> +	if (input.config_address) {
>> +		if (copy_to_user((void * __user)input.config_address,
>> +				 &sev->snp_config, sizeof(struct sev_user_data_snp_config)))
>> +			return -EFAULT;
>> +	}
>> +
>> +	/* Copy the extended certs programmed through the SNP_SET_CONFIG */
>> +	if (input.certs_address && sev->snp_certs_data) {
>> +		if (input.certs_len < sev->snp_certs_len) {
>> +			/* Return the certs length to userspace */
>> +			input.certs_len = sev->snp_certs_len;
>> +
>> +			ret = -ENOSR;

We should be consistent with the other SEV ioctls that return required 
lengths and return -EIO here instead -ENOSR.

Thanks,
Tom

>> +			goto e_done;
>> +		}
>> +
> 
> What about if input.certs_len > sev->snp_certs_len? Is it possbile for the
> userspace to know the length of data in the buffer? (I guess it might be able
> to know the certs len through the blob data, but a comment here would be nice)
> 
>> +		if (copy_to_user((void * __user)input.certs_address,
>> +				 sev->snp_certs_data, sev->snp_certs_len))
>> +			return -EFAULT;
>> +	}
>> +
>> +	ret = 0;
>> +
>> +e_done:
>> +	if (copy_to_user((void __user *)argp->data, &input, sizeof(input)))
>> +		ret = -EFAULT;
>> +
>> +	return ret;
>> +}