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

Michael S. Tsirkin
2022-06-22T07:03:09Z

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.

> ---
> 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