Date:   Fri, 24 Jun 2022 05:05:07 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
Cc:     Jason Wang <jasowang@...hat.com>, ben@...adent.org.uk,
        cohuck@...hat.com, pasic@...ux.ibm.com, hca@...ux.ibm.com,
        gor@...ux.ibm.com, borntraeger@...ibm.com, agordeev@...ux.ibm.com,
        linux-s390@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH V3] virtio: disable notification hardening by default

On Fri, Jun 24, 2022 at 04:41:55PM +0800, Xuan Zhuo wrote:
> On Wed, 22 Jun 2022 09:29:40 +0800, Jason Wang <jasowang@...hat.com> 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.
> 
> 
> hi, I have a question.
> 
> What should we do when the queue is reset and CONFIG_VIRTIO_HARDEN_NOTIFICATION
> is off?
> 
> Since disable_irq() cannot be used, we should trust the device not to send irqs
> again. So we don't have to do anything?

yes

> Thanks.
> 
> >
> > Signed-off-by: Jason Wang <jasowang@...hat.com>
> > ---
> > 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
> >
> > _______________________________________________
> > Virtualization mailing list
> > Virtualization@...ts.linux-foundation.org
> > https://lists.linuxfoundation.org/mailman/listinfo/virtualization

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