Date:   Thu, 23 Feb 2023 08:19:31 -0600
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Zhi Wang <zhi.wang.linux@...il.com>,
        "Kalra, Ashish" <ashish.kalra@....com>
Cc:     Michael Roth <michael.roth@....com>, 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, 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 2/23/23 00:38, Zhi Wang wrote:
> On Wed, 22 Feb 2023 16:43:54 -0600
> "Kalra, Ashish" <ashish.kalra@....com> wrote:
> 
>> On 2/22/2023 6:32 AM, 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/Documentation/virt/coco/sev-guest.rst b/Documentation/virt/coco/sev-guest.rst
>>>> index 11ea67c944df..6cad4226c348 100644
>>>> --- a/Documentation/virt/coco/sev-guest.rst
>>>> +++ b/Documentation/virt/coco/sev-guest.rst
>>>> @@ -145,6 +145,33 @@ The SNP_PLATFORM_STATUS command is used to query the SNP platform status. The
>>>>    status includes API major, minor version and more. See the SEV-SNP
>>>>    specification for further details.
>>>>    
>>>> +2.5 SNP_SET_EXT_CONFIG
>>>> +----------------------
>>>> +:Technology: sev-snp
>>>> +:Type: hypervisor ioctl cmd
>>>> +:Parameters (in): struct sev_data_snp_ext_config
>>>> +:Returns (out): 0 on success, -negative on error
>>>> +
>>>> +The SNP_SET_EXT_CONFIG is used to set the system-wide configuration such as
>>>> +reported TCB version in the attestation report. The command is similar to
>>>> +SNP_CONFIG command defined in the SEV-SNP spec. The main difference is the
>>>> +command also accepts an additional certificate blob defined in the GHCB
>>>> +specification.
>>>> +
>>>> +If the certs_address is zero, then the previous certificate blob will deleted.
>>>> +For more information on the certificate blob layout, see the GHCB spec
>>>> +(extended guest request message).
>>>> +
>>>> +2.6 SNP_GET_EXT_CONFIG
>>>> +----------------------
>>>> +:Technology: sev-snp
>>>> +:Type: hypervisor ioctl cmd
>>>> +:Parameters (in): struct sev_data_snp_ext_config
>>>> +:Returns (out): 0 on success, -negative on error
>>>> +
>>>> +The SNP_GET_EXT_CONFIG is used to query the system-wide configuration set
>>>> +through the SNP_SET_EXT_CONFIG.
>>>> +
>>>>    3. SEV-SNP CPUID Enforcement
>>>>    ============================
>>>>    
>>>> 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;
>>>> +			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 userspace provides an input buffer/length smaller then snp_certs_len,
>> then the above returns the "required" certs length back to userspace.
>>
>> And what is the issue if input.certs_len > sev->snp_certs_len, the
>> buffer returned back to userspace is sev->snp_certs_len as below.
>>
> 
> My point is: How can the userspace know the length of return data is shorter
> than input.certs_len when input.certs_len > sev->snp_serts_len? as the length
> is only returned when input.certs_len < sev->snp_certs_len.

The returned data has a defined format that can be used to calculate the 
overall length.

Thanks,
Tom

> 
>> Thanks,
>> Ashish
>>
>>>> +		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;
>>>> +}
>>>> +
>>>> +static int sev_ioctl_snp_set_config(struct sev_issue_cmd *argp, bool writable)
>>>> +{
>>>> +	struct sev_device *sev = psp_master->sev_data;
>>>> +	struct sev_user_data_ext_snp_config input;
>>>> +	struct sev_user_data_snp_config config;
>>>> +	void *certs = NULL;
>>>> +	int ret = 0;
>>>> +
>>>> +	if (!sev->snp_initialized || !argp->data)
>>>> +		return -EINVAL;
>>>> +
>>>> +	if (!writable)
>>>> +		return -EPERM;
>>>> +
>>>> +	memset(&input, 0, sizeof(input));
>>>> +
>>>> +	if (copy_from_user(&input, (void __user *)argp->data, sizeof(input)))
>>>> +		return -EFAULT;
>>>> +
>>>> +	/* Copy the certs from userspace */
>>>> +	if (input.certs_address) {
>>>> +		if (!input.certs_len || !IS_ALIGNED(input.certs_len, PAGE_SIZE))
>>>> +			return -EINVAL;
>>>> +
>>>> +		certs = psp_copy_user_blob(input.certs_address, input.certs_len);
>>>> +		if (IS_ERR(certs))
>>>> +			return PTR_ERR(certs);
>>>> +	}
>>>> +
>>>> +	/* Issue the PSP command to update the TCB version using the SNP_CONFIG. */
>>>> +	if (input.config_address) {
>>>> +		memset(&config, 0, sizeof(config));
>>>> +		if (copy_from_user(&config,
>>>> +				   (void __user *)input.config_address, sizeof(config))) {
>>>> +			ret = -EFAULT;
>>>> +			goto e_free;
>>>> +		}
>>>> +
>>>> +		ret = __sev_do_cmd_locked(SEV_CMD_SNP_CONFIG, &config, &argp->error);
>>>> +		if (ret)
>>>> +			goto e_free;
>>>> +
>>>> +		memcpy(&sev->snp_config, &config, sizeof(config));
>>>> +	}
>>>> +
>>>> +	/*
>>>> +	 * If the new certs are passed then cache it else free the old certs.
>>>> +	 */
>>>> +	mutex_lock(&sev->snp_certs_lock);
>>>> +	if (certs) {
>>>> +		kfree(sev->snp_certs_data);
>>>> +		sev->snp_certs_data = certs;
>>>> +		sev->snp_certs_len = input.certs_len;
>>>> +	} else {
>>>> +		kfree(sev->snp_certs_data);
>>>> +		sev->snp_certs_data = NULL;
>>>> +		sev->snp_certs_len = 0;
>>>> +	}
>>>> +	mutex_unlock(&sev->snp_certs_lock);
>>>> +
>>>> +	return 0;
>>>> +
>>>> +e_free:
>>>> +	kfree(certs);
>>>> +	return ret;
>>>> +}
>>>> +
>>>>    static long sev_ioctl(struct file *file, unsigned int ioctl, unsigned long arg)
>>>>    {
>>>>    	void __user *argp = (void __user *)arg;
>>>> @@ -1847,6 +1963,12 @@ static long sev_ioctl(struct file *file, unsigned int ioctl, unsigned long arg)
>>>>    	case SNP_PLATFORM_STATUS:
>>>>    		ret = sev_ioctl_snp_platform_status(&input);
>>>>    		break;
>>>> +	case SNP_SET_EXT_CONFIG:
>>>> +		ret = sev_ioctl_snp_set_config(&input, writable);
>>>> +		break;
>>>> +	case SNP_GET_EXT_CONFIG:
>>>> +		ret = sev_ioctl_snp_get_config(&input);
>>>> +		break;
>>>>    	default:
>>>>    		ret = -EINVAL;
>>>>    		goto out;
>>>> @@ -1962,6 +2084,7 @@ int sev_dev_init(struct psp_device *psp)
>>>>    		goto e_sev;
>>>>    
>>>>    	sev->cmd_buf_backup = (uint8_t *)sev->cmd_buf + PAGE_SIZE;
>>>> +	mutex_init(&sev->snp_certs_lock);
>>>>    
>>>>    	psp->sev_data = sev;
>>>>    
>>>> diff --git a/drivers/crypto/ccp/sev-dev.h b/drivers/crypto/ccp/sev-dev.h
>>>> index 19d79f9d4212..41d5353d5bab 100644
>>>> --- a/drivers/crypto/ccp/sev-dev.h
>>>> +++ b/drivers/crypto/ccp/sev-dev.h
>>>> @@ -66,6 +66,10 @@ struct sev_device {
>>>>    
>>>>    	bool snp_initialized;
>>>>    	struct snp_host_map snp_host_map[MAX_SNP_HOST_MAP_BUFS];
>>>> +	void *snp_certs_data;
>>>> +	u32 snp_certs_len;
>>>> +	struct mutex snp_certs_lock;
>>>> +	struct sev_user_data_snp_config snp_config;
>>>>    };
>>>>    
>>>>    int sev_dev_init(struct psp_device *psp);
>>>> diff --git a/include/uapi/linux/psp-sev.h b/include/uapi/linux/psp-sev.h
>>>> index 5adfaea7df97..c20d37586d21 100644
>>>> --- a/include/uapi/linux/psp-sev.h
>>>> +++ b/include/uapi/linux/psp-sev.h
>>>> @@ -29,6 +29,8 @@ enum {
>>>>    	SEV_GET_ID,	/* This command is deprecated, use SEV_GET_ID2 */
>>>>    	SEV_GET_ID2,
>>>>    	SNP_PLATFORM_STATUS,
>>>> +	SNP_SET_EXT_CONFIG,
>>>> +	SNP_GET_EXT_CONFIG,
>>>>    
>>>>    	SEV_MAX,
>>>>    };
>>>> @@ -192,6 +194,21 @@ struct sev_user_data_snp_config {
>>>>    	__u8 rsvd1[52];
>>>>    } __packed;
>>>>    
>>>> +/**
>>>> + * struct sev_data_snp_ext_config - system wide configuration value for SNP.
>>>> + *
>>>> + * @config_address: address of the struct sev_user_data_snp_config or 0 when
>>>> + *		reported_tcb does not need to be updated.
>>>> + * @certs_address: address of extended guest request certificate chain or
>>>> + *              0 when previous certificate should be removed on SNP_SET_EXT_CONFIG.
>>>> + * @certs_len: length of the certs
>>>> + */
>>>> +struct sev_user_data_ext_snp_config {
>>>> +	__u64 config_address;		/* In */
>>>> +	__u64 certs_address;		/* In */
>>>> +	__u32 certs_len;		/* In */
>>>> +};
>>>> +
>>>>    /**
>>>>     * struct sev_issue_cmd - SEV ioctl parameters
>>>>     *
>>>
> 

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