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 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;
> > >    }