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

[Peter Gonda]

On Mon, May 16, 2022 at 9:02 AM Kalra, Ashish <Ashish.Kalra@xxxxxxx> wrote:
>
> [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.

That does seem safe for now but I thought we decided it would be
prudent to not trust the PSPs implementation here and clear all the
buffers that eventually get sent to userspace?

>
> Thanks,
> Ashish