linux-kernel - RE: [PATCH Part2 v6 17/49] crypto: ccp: Add the SNP_{SET,GET}_EXT

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Message-ID: <BYAPR12MB2759B6CBC481A4A45167589A8EB29@BYAPR12MB2759.namprd12.prod.outlook.com>
Date:   Wed, 22 Jun 2022 01:58:09 +0000
From:   "Kalra, Ashish" <Ashish.Kalra@....com>
To:     Peter Gonda <pgonda@...gle.com>
CC:     the arch/x86 maintainers <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
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        Thomas Gleixner <tglx@...utronix.de>,
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Subject: RE: [PATCH Part2 v6 17/49] crypto: ccp: Add the
 SNP_{SET,GET}_EXT_CONFIG command

[AMD Official Use Only - General]

Hello Peter,

>> +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;

>Lets memset |input| to zero to avoid leaking kernel memory, see
>"crypto: ccp - Use kzalloc for sev ioctl interfaces to prevent kernel memory leak"

Yes. 

>> +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_inited || !argp->data)
>> +               return -EINVAL;
>> +
>> +       if (!writable)
>> +               return -EPERM;
>> +
>> +       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);

>I see that psp_copy_user_blob() uses memdup_user() which tracks the allocated memory to GFP_USER. Given this memory is long lived and now belongs to the PSP driver in perpetuity, should this be tracked with GFP_KERNEL?

But we need to copy from user space address, so what is the alternative here ?

>> +       /*
>> +        * If the new certs are passed then cache it else free the old certs.
>> +        */
>> +       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;
>> +       }

>Do we need another lock here? When I look at 18/49 it seems like
>snp_guest_ext_guest_request() it seems like we have a race for
>|sev->snp_certs_data|

The certificate blob in snp_guest_ext_guest_request() will depend on the 
certificate blob provided here by SNP_SET_EXT_CONFIG. There might be a potential 
race with the SNP extended guest request NAE, let me have a look at it.

>>         bool snp_inited;
>>         struct snp_host_map snp_host_map[MAX_SNP_HOST_MAP_BUFS];
>> +       void *snp_certs_data;
>> +       u32 snp_certs_len;
>> +       struct sev_user_data_snp_config snp_config;

>Since this gets copy_to_user'd can we memset this to 0 to prevent leaking kernel uninitialized memory? Similar to recent patches with kzalloc and __GPF_ZERO usage.

Yes.

Thanks,
Ashish