Re: [Qemu-devel] [PATCH] virtio: destroy region cache during reset

[Paolo Bonzini <pbonzini@redhat.com>]

----- Original Message -----
> From: "Jason Wang" <jasowang@redhat.com>
> To: "Paolo Bonzini" <pbonzini@redhat.com>, mst@redhat.com, qemu-devel@nongnu.org
> Cc: peterx@redhat.com
> Sent: Wednesday, March 8, 2017 7:22:06 AM
> Subject: Re: [Qemu-devel] [PATCH] virtio: destroy region cache during reset
> 
> 
> 
> On 2017年03月08日 11:21, Jason Wang wrote:
> >
> > On 2017年03月07日 18:55, Paolo Bonzini wrote:
> >>
> >> On 07/03/2017 09:47, Jason Wang wrote:
> >>> We don't destroy region cache during reset which can make the maps
> >>> of previous driver leaked to a buggy or malicious driver that don't
> >>> set vring address before starting to use the device.
> >> I'm still not sure as to how this can happen.  Reset does clear
> >> desc/used/avail, which should then be checked before accessing the
> >> caches.
> >
> > But the code does not check them in fact? (E.g the attached qtest
> > patch can still pass check-qtest).
> >
> > Thanks
> 
> Ok, the reproducer seems wrong. And I think what you mean is something
> like the check done in virtio_queue_ready(). But looks like not all
> virtqueue check for this. One example is virtio_net_handle_ctrl(), and
> there may be even more. So you want to fix them all?

Why would virtio_net_handle_ctrl be called when desc == 0?  The checks
are all in common virtio code.

static void virtio_queue_notify_vq(VirtQueue *vq)
{
    if (vq->vring.desc && vq->handle_output) {
        VirtIODevice *vdev = vq->vdev;

        if (unlikely(vdev->broken)) {
            return;
        }

        trace_virtio_queue_notify(vdev, vq - vdev->vq, vq);
        vq->handle_output(vdev, vq);
    }
}
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Paolo