Date:   Fri, 24 Jun 2022 02:31:46 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     Cornelia Huck <cohuck@...hat.com>,
        Halil Pasic <pasic@...ux.ibm.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        linux-s390@...r.kernel.org,
        virtualization <virtualization@...ts.linux-foundation.org>,
        kvm <kvm@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Ben Hutchings <ben@...adent.org.uk>,
        David Hildenbrand <david@...hat.com>
Subject: Re: [PATCH V3] virtio: disable notification hardening by default

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@...hat.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@...hat.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
> >

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