Re: [PATCH V3] virtio: disable notification hardening by default

Michael S. Tsirkin
2022-06-24T06:32:00Z

On Wed, Jun 22, 2022 at 03:09:31PM +0800, Jason Wang wrote:
> On Wed, Jun 22, 2022 at 3:03 PM Michael S. Tsirkin <mst@redhat.com> wrote:
> >
> > On Wed, Jun 22, 2022 at 09:29:40AM +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@redhat.com>
> >
> >
> > OK I will queue, but I think the problem is fundamental.
>
> If I understand correctly, you want some core IRQ work?

Yes.

> As discussed
> before, it doesn't solve all the problems, we still need to do per
> driver audit.
>
> Thanks

Maybe, but we don't need to tie things to device_ready then.
We can do

- disable irqs
- device ready
- setup everything
- enable irqs

and this works for most things, the only issue is
this deadlocks if "setup everything" waits for interrupts.

With the current approach there's really no good time:
1.- setup everything
- device ready

can cause kicks before device is ready

2.- device ready
- setup everything

can cause callbacks before setup.

So I prefer the 1. and fix the hardening in the core.

> >
> >
> > > ---
> > > Changes since V2:
> > > - Tweak the Kconfig help
> > > - Add comment for the read_lock() pairing in virtio_ccw
> > > ---
> > > drivers/s390/virtio/virtio_ccw.c | 9 ++++++++-
> > > drivers/virtio/Kconfig | 13 +++++++++++++
> > > drivers/virtio/virtio.c | 2 ++
> > > drivers/virtio/virtio_ring.c | 12 ++++++++++++
> > > include/linux/virtio_config.h | 2 ++
> > > 5 files changed, 37 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/s390/virtio/virtio_ccw.c b/drivers/s390/virtio/virtio_ccw.c
> > > index 97e51c34e6cf..1f6a358f65f0 100644
> > > --- a/drivers/s390/virtio/virtio_ccw.c
> > > +++ b/drivers/s390/virtio/virtio_ccw.c
> > > @@ -1136,8 +1136,13 @@ static void virtio_ccw_int_handler(struct ccw_device *cdev,
> > > vcdev->err = -EIO;
> > > }
> > > virtio_ccw_check_activity(vcdev, activity);
> > > - /* Interrupts are disabled here */
> > > +#ifdef CONFIG_VIRTIO_HARDEN_NOTIFICATION
> > > + /*
> > > + * Paried with virtio_ccw_synchronize_cbs() and interrupts are
> > > + * disabled here.
> > > + */
> > > read_lock(&vcdev->irq_lock);
> > > +#endif
> > > for_each_set_bit(i, indicators(vcdev),
> > > sizeof(*indicators(vcdev)) * BITS_PER_BYTE) {
> > > /* The bit clear must happen before the vring kick. */
> > > @@ -1146,7 +1151,9 @@ static void virtio_ccw_int_handler(struct ccw_device *cdev,
> > > vq = virtio_ccw_vq_by_ind(vcdev, i);
> > > vring_interrupt(0, vq);
> > > }
> > > +#ifdef CONFIG_VIRTIO_HARDEN_NOTIFICATION
> > > read_unlock(&vcdev->irq_lock);
> > > +#endif
> > > if (test_bit(0, indicators2(vcdev))) {
> > > virtio_config_changed(&vcdev->vdev);
> > > clear_bit(0, indicators2(vcdev));
> > > diff --git a/drivers/virtio/Kconfig b/drivers/virtio/Kconfig
> > > index b5adf6abd241..c04f370a1e5c 100644
> > > --- a/drivers/virtio/Kconfig
> > > +++ b/drivers/virtio/Kconfig
> > > @@ -35,6 +35,19 @@ menuconfig VIRTIO_MENU
> > >
> > > if VIRTIO_MENU
> > >
> > > +config VIRTIO_HARDEN_NOTIFICATION
> > > + bool "Harden virtio notification"
> > > + help
> > > + Enable this to harden the device notifications and suppress
> > > + those that happen at a time where notifications are illegal.
> > > +
> > > + Experimental: Note that several drivers still have bugs that
> > > + may cause crashes or hangs when correct handling of
> > > + notifications is enforced; depending on the subset of
> > > + drivers and devices you use, this may or may not work.
> > > +
> > > + If unsure, say N.
> > > +
> > > 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
> >