Re: [PATCH-for-9.0 3/4] hw/char/virtio-serial-bus: Protect from DMA re-entrancy bugs

[Philippe Mathieu-Daudé]

On 8/4/24 17:20, Michael S. Tsirkin wrote:
> On Mon, Apr 08, 2024 at 01:04:11PM +0200, Philippe Mathieu-Daudé wrote:
> > On 8/4/24 12:08, Michael S. Tsirkin wrote:
> > > On Mon, Apr 08, 2024 at 09:14:39AM +0200, Philippe Mathieu-Daudé wrote:
> > > > On 4/4/24 21:13, Philippe Mathieu-Daudé wrote:
> > > > > Replace qemu_bh_new_guarded() by virtio_bh_new_guarded()
> > > > > so the bus and device use the same guard. Otherwise the
> > > > > DMA-reentrancy protection can be bypassed.
> > > > >
> > > > > Cc: qemu-stable@nongnu.org
> > > > > Suggested-by: Alexander Bulekov <alxndr@bu.edu>
> > > > > Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
> > > > > ---
> > > > >     hw/char/virtio-serial-bus.c | 3 +--
> > > > >     1 file changed, 1 insertion(+), 2 deletions(-)
> > > > >
> > > > > diff --git a/hw/char/virtio-serial-bus.c b/hw/char/virtio-serial-bus.c
> > > > > index 016aba6374..cd0e3a11f7 100644
> > > > > --- a/hw/char/virtio-serial-bus.c
> > > > > +++ b/hw/char/virtio-serial-bus.c
> > > > > @@ -985,8 +985,7 @@ static void virtser_port_device_realize(DeviceState *dev, 
> > > > > Error **errp)
> > > > >             return;
> > > > >         }
> > > > > -    port->bh = qemu_bh_new_guarded(flush_queued_data_bh, port,
> > > > > -                                   &dev->mem_reentrancy_guard);
> > > > > +    port->bh = virtio_bh_new_guarded(vdev, flush_queued_data_bh, port);
> > > >
> > > > Missing:
> > > > -- >8 --
> > > > -    port->bh = virtio_bh_new_guarded(vdev, flush_queued_data_bh, port);
> > > > +    port->bh = virtio_bh_new_guarded(VIRTIO_DEVICE(dev),
> > > > +                                     flush_queued_data_bh, port);
> > > > ---
> > >
> > > I don't get it. vdev is already the correct type. Why do you need
> > > VIRTIO_DEVICE here?
> >
> > This function doesn't declare vdev.
> >
> > > > >         port->elem = NULL;
> > > > >     }
>
>
>
> But it seems clear it wasn't really tested, right?

Indeed, I only tested virtio-gpu, then added the other ones Alexander
suggested. I don't have virtio-specific tests, I rely on the GitLab CI
ones. Hope that's enough.

> Philipe here's my ack:
>
> Acked-by: Michael S. Tsirkin <mst@redhat.com>
>
> Feel free to merge these after testing.

Sure, thanks!

Phil.