[PATCH] virtio: disable notification hardening by default

[Jason Wang]

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>
---
 drivers/virtio/Kconfig        |  6 ++++++
 drivers/virtio/virtio.c       |  2 ++
 drivers/virtio/virtio_ring.c  | 12 ++++++++++++
 include/linux/virtio_config.h |  2 ++
 4 files changed, 22 insertions(+)

diff --git a/drivers/virtio/Kconfig b/drivers/virtio/Kconfig
index b5adf6abd241..b059c39af3d4 100644
--- a/drivers/virtio/Kconfig
+++ b/drivers/virtio/Kconfig
@@ -35,6 +35,12 @@ menuconfig VIRTIO_MENU
 
 if VIRTIO_MENU
 
+config VIRTIO_HARDEN_NOTIFICATION
+        bool "Harden virtio notification"
+        help
+          Enable to this to harden the device notifications and
+          supress the ones that are illegal.
+
 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