RE: [PATCH v2] crypto: ccp - Use kzalloc for sev ioctl interfaces to prevent kernel memory leak

[Kalra, Ashish]

[AMD Official Use Only - General]

Hello Peter,

-----Original Message-----
From: Peter Gonda <pgonda@xxxxxxxxxx> 
Sent: Monday, May 16, 2022 10:53 AM
To: Allen, John <John.Allen@xxxxxxx>
Cc: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>; Linux Crypto Mailing List <linux-crypto@xxxxxxxxxxxxxxx>; Sean Christopherson <seanjc@xxxxxxxxxx>; Lendacky, Thomas <Thomas.Lendacky@xxxxxxx>; Kalra, Ashish <Ashish.Kalra@xxxxxxx>; LKML <linux-kernel@xxxxxxxxxxxxxxx>; Andy Nguyen <theflow@xxxxxxxxxx>; David Rientjes <rientjes@xxxxxxxxxx>; stable@xxxxxxxxxxxxxxx
Subject: Re: [PATCH v2] crypto: ccp - Use kzalloc for sev ioctl interfaces to prevent kernel memory leak

On Mon, May 16, 2022 at 8:46 AM John Allen <john.allen@xxxxxxx> wrote:
>
> For some sev ioctl interfaces, input may be passed that is less than 
> or equal to SEV_FW_BLOB_MAX_SIZE, but larger than the data that PSP 
> firmware returns. In this case, kmalloc will allocate memory that is 
> the size of the input rather than the size of the data. Since PSP 
> firmware doesn't fully overwrite the buffer, the sev ioctl interfaces 
> with the issue may return uninitialized slab memory.
>
> Currently, all of the ioctl interfaces in the ccp driver are safe, but 
> to prevent future problems, change all ioctl interfaces that allocate 
> memory with kmalloc to use kzalloc.
>
> Fixes: e799035609e15 ("crypto: ccp: Implement SEV_PEK_CSR ioctl 
> command")
> Fixes: 76a2b524a4b1d ("crypto: ccp: Implement SEV_PDH_CERT_EXPORT 
> ioctl command")
> Fixes: d6112ea0cb344 ("crypto: ccp - introduce SEV_GET_ID2 command")
> Cc: stable@xxxxxxxxxxxxxxx
> Reported-by: Andy Nguyen <theflow@xxxxxxxxxx>
> Suggested-by: David Rientjes <rientjes@xxxxxxxxxx>
> Suggested-by: Peter Gonda <pgonda@xxxxxxxxxx>
> Signed-off-by: John Allen <john.allen@xxxxxxx>
> ---
> v2:
>   - Add fixes tags and CC stable@xxxxxxxxxxxxxxx
> ---


>static int sev_ioctl_do_platform_status(struct sev_issue_cmd *argp) { struct sev_user_data_status data; int ret;

>ret = __sev_do_cmd_locked(SEV_CMD_PLATFORM_STATUS, &data, &argp->error); if (ret) return ret;

>if (copy_to_user((void __user *)argp->data, &data, sizeof(data))) ret = -EFAULT;

>return ret;
>}

>Would it be safer to memset @data here to all zeros too?

It will be, but this command/function is safe as firmware will fill in the whole buffer here with the PLATFORM STATUS data retuned to the user.

Thanks,
Ashish