Commit c346dae4 authored by Jason Wang's avatar Jason Wang Committed by Michael S. Tsirkin
Browse files

virtio: disable notification hardening by default 



We try to harden virtio device notifications in 8b4ec69d ("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 add a Kconfig option and disable it by default. It gives
us time to fix the drivers and then we can consider re-enabling it.

Signed-off-by: default avatarJason Wang <jasowang@redhat.com>
Message-Id: <20220622012940.21441-1-jasowang@redhat.com>
Signed-off-by: default avatarMichael S. Tsirkin <mst@redhat.com>
Reviewed-by: default avatarCornelia Huck <cohuck@redhat.com>
parent 03d95717

drivers/s390/virtio/virtio_ccw.c

+8 −1
Original line number Diff line number Diff line
@@ -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

	/*

	 * Paired 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));

drivers/virtio/Kconfig

+13 −0
Original line number Diff line number Diff line
@@ -29,6 +29,19 @@ 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

drivers/virtio/virtio.c

+2 −0
Original line number Diff line number Diff line
@@ -219,6 +219,7 @@ 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
@@ -227,6 +228,7 @@ void virtio_reset_device(struct virtio_device *dev) 
	 */

	virtio_break_device(dev);

	virtio_synchronize_cbs(dev);

#endif



	dev->config->reset(dev);

}

drivers/virtio/virtio_ring.c

+12 −0
Original line number Diff line number Diff line
@@ -1708,7 +1708,11 @@ 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 | (1 << VRING_PACKED_EVENT_F_WRAP_CTR);

	vq->event_triggered = false;

	vq->num_added = 0;
@@ -2154,9 +2158,13 @@ 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! */
@@ -2199,7 +2207,11 @@ 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;

include/linux/virtio_config.h

+2 −0
Original line number Diff line number Diff line
@@ -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