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

[Michael S. Tsirkin]

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@xxxxxxxxxx>


OK I will queue, but I think the problem is fundamental.


> ---
> 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