Re: [PATCH V5 1/4] virtio_ring: validate used buffer length

[Jason Wang]

On Fri, Nov 19, 2021 at 11:10 PM Halil Pasic <pasic@xxxxxxxxxxxxx> wrote:
>
> On Wed, 27 Oct 2021 10:21:04 +0800
> Jason Wang <jasowang@xxxxxxxxxx> wrote:
>
> > This patch validate the used buffer length provided by the device
> > before trying to use it. This is done by record the in buffer length
> > in a new field in desc_state structure during virtqueue_add(), then we
> > can fail the virtqueue_get_buf() when we find the device is trying to
> > give us a used buffer length which is greater than the in buffer
> > length.
> >
> > Since some drivers have already done the validation by themselves,
> > this patch tries to makes the core validation optional. For the driver
> > that doesn't want the validation, it can set the
> > suppress_used_validation to be true (which could be overridden by
> > force_used_validation module parameter). To be more efficient, a
> > dedicate array is used for storing the validate used length, this
> > helps to eliminate the cache stress if validation is done by the
> > driver.
> >
> > Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
>
> Hi Jason!
>
> Our CI has detected, that virtio-vsock became unusable with this
> patch on s390x. I didn't test on x86 yet. The guest kernel says
> something like:
> vmw_vsock_virtio_transport virtio1: tx: used len 44 is larger than in buflen 0
>
> Did you, or anybody else, see something like this on platforms other that
> s390x?

Adding Stefan and Stefano.

I think it should be a common issue, looking at
vhost_vsock_handle_tx_kick(), it did:

len += sizeof(pkt->hdr);
vhost_add_used(vq, head, len);

which looks like a violation of the spec since it's TX.

>
> I had a quick look at this code, and I speculate that it probably
> uncovers a pre-existig bug, rather than introducing a new one.

I agree.

>
> If somebody is already working on this please reach out to me.

AFAIK, no. I think the plan is to fix both the device and drive side
(but I'm not sure we need a new feature for this if we stick to the
validation).

Thanks

>
> Regards,
> Halil
>