Re: [PATCH] virtio: disable notification hardening by default

[Michael S. Tsirkin]

On Fri, Jun 17, 2022 at 07:47:21PM +0800, Jason Wang wrote:
> On Fri, Jun 17, 2022 at 6:01 PM Michael S. Tsirkin <mst@xxxxxxxxxx> wrote:
> >
> > On Fri, Jun 17, 2022 at 03:26:26PM +0800, Jason Wang wrote:
> > > We try to harden virtio device notifications in 8b4ec69d7e09 ("virtio:
> > > harden vring IRQ"). It works with the assumption that the driver or
> > > core can properly call virtio_device_ready() at the right
> > > place. Unfortunately, this seems to be not true and uncover various
> > > bugs of the existing drivers, mainly the issue of using
> > > virtio_device_ready() incorrectly.
> > >
> > > So let's having a Kconfig option and disable it by default. It gives
> > > us a breath to fix the drivers and then we can consider to enable it
> > > by default.
> > >
> > > Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
> >
> >
> > Do you want to drop irq_lock lock/unlock in ccw too?
> 
> Not a must I think. But if you insist, I can remove them.
> 
> Thanks


With the ifdef. Seems safer ...

> >
> > > ---
> > >  drivers/virtio/Kconfig        |  6 ++++++
> > >  drivers/virtio/virtio.c       |  2 ++
> > >  drivers/virtio/virtio_ring.c  | 12 ++++++++++++
> > >  include/linux/virtio_config.h |  2 ++
> > >  4 files changed, 22 insertions(+)
> > >
> > > diff --git a/drivers/virtio/Kconfig b/drivers/virtio/Kconfig
> > > index b5adf6abd241..b059c39af3d4 100644
> > > --- a/drivers/virtio/Kconfig
> > > +++ b/drivers/virtio/Kconfig
> > > @@ -35,6 +35,12 @@ menuconfig VIRTIO_MENU
> > >
> > >  if VIRTIO_MENU
> > >
> > > +config VIRTIO_HARDEN_NOTIFICATION
> > > +        bool "Harden virtio notification"
> > > +        help
> > > +          Enable to this to harden the device notifications and
> > > +          supress the ones that are illegal.
> > > +
> > >  config VIRTIO_PCI
> > >       tristate "PCI driver for virtio devices"
> > >       depends on PCI
> > > diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
> > > index ef04a96942bf..21dc08d2f32d 100644
> > > --- a/drivers/virtio/virtio.c
> > > +++ b/drivers/virtio/virtio.c
> > > @@ -220,6 +220,7 @@ static int virtio_features_ok(struct virtio_device *dev)
> > >   * */
> > >  void virtio_reset_device(struct virtio_device *dev)
> > >  {
> > > +#ifdef CONFIG_VIRTIO_HARDEN_NOTIFICATION
> > >       /*
> > >        * The below virtio_synchronize_cbs() guarantees that any
> > >        * interrupt for this line arriving after
> > > @@ -228,6 +229,7 @@ void virtio_reset_device(struct virtio_device *dev)
> > >        */
> > >       virtio_break_device(dev);
> > >       virtio_synchronize_cbs(dev);
> > > +#endif
> > >
> > >       dev->config->reset(dev);
> > >  }
> > > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> > > index 13a7348cedff..d9d3b6e201fb 100644
> > > --- a/drivers/virtio/virtio_ring.c
> > > +++ b/drivers/virtio/virtio_ring.c
> > > @@ -1688,7 +1688,11 @@ static struct virtqueue *vring_create_virtqueue_packed(
> > >       vq->we_own_ring = true;
> > >       vq->notify = notify;
> > >       vq->weak_barriers = weak_barriers;
> > > +#ifdef CONFIG_VIRTIO_HARDEN_NOTIFICATION
> > >       vq->broken = true;
> > > +#else
> > > +     vq->broken = false;
> > > +#endif
> > >       vq->last_used_idx = 0;
> > >       vq->event_triggered = false;
> > >       vq->num_added = 0;
> > > @@ -2135,9 +2139,13 @@ irqreturn_t vring_interrupt(int irq, void *_vq)
> > >       }
> > >
> > >       if (unlikely(vq->broken)) {
> > > +#ifdef CONFIG_VIRTIO_HARDEN_NOTIFICATION
> > >               dev_warn_once(&vq->vq.vdev->dev,
> > >                             "virtio vring IRQ raised before DRIVER_OK");
> > >               return IRQ_NONE;
> > > +#else
> > > +             return IRQ_HANDLED;
> > > +#endif
> > >       }
> > >
> > >       /* Just a hint for performance: so it's ok that this can be racy! */
> > > @@ -2180,7 +2188,11 @@ struct virtqueue *__vring_new_virtqueue(unsigned int index,
> > >       vq->we_own_ring = false;
> > >       vq->notify = notify;
> > >       vq->weak_barriers = weak_barriers;
> > > +#ifdef CONFIG_VIRTIO_HARDEN_NOTIFICATION
> > >       vq->broken = true;
> > > +#else
> > > +     vq->broken = false;
> > > +#endif
> > >       vq->last_used_idx = 0;
> > >       vq->event_triggered = false;
> > >       vq->num_added = 0;
> > > diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h
> > > index 9a36051ceb76..d15c3cdda2d2 100644
> > > --- a/include/linux/virtio_config.h
> > > +++ b/include/linux/virtio_config.h
> > > @@ -257,6 +257,7 @@ void virtio_device_ready(struct virtio_device *dev)
> > >
> > >       WARN_ON(status & VIRTIO_CONFIG_S_DRIVER_OK);
> > >
> > > +#ifdef CONFIG_VIRTIO_HARDEN_NOTIFICATION
> > >       /*
> > >        * The virtio_synchronize_cbs() makes sure vring_interrupt()
> > >        * will see the driver specific setup if it sees vq->broken
> > > @@ -264,6 +265,7 @@ void virtio_device_ready(struct virtio_device *dev)
> > >        */
> > >       virtio_synchronize_cbs(dev);
> > >       __virtio_unbreak_device(dev);
> > > +#endif
> > >       /*
> > >        * The transport should ensure the visibility of vq->broken
> > >        * before setting DRIVER_OK. See the comments for the transport
> > > --
> > > 2.25.1
> >