[PATCH V3] virtio: disable notification hardening by default

Jason Wang
2022-06-22T01:29:56Z

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>
---
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