Jason Wang
2022-Jun-20 02:41 UTC
[PATCH V2] virtio: disable notification hardening by default
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 at redhat.com>
---
Changes since V1:
- tweak the Kconfig prompt
- don't hold spinlock for IRQ path in s390
---
drivers/s390/virtio/virtio_ccw.c | 4 ++++
drivers/virtio/Kconfig | 11 +++++++++++
drivers/virtio/virtio.c | 2 ++
drivers/virtio/virtio_ring.c | 12 ++++++++++++
include/linux/virtio_config.h | 2 ++
5 files changed, 31 insertions(+)
diff --git a/drivers/s390/virtio/virtio_ccw.c b/drivers/s390/virtio/virtio_ccw.c
index 97e51c34e6cf..89bbf7ccfdd1 100644
--- a/drivers/s390/virtio/virtio_ccw.c
+++ b/drivers/s390/virtio/virtio_ccw.c
@@ -1136,8 +1136,10 @@ static void virtio_ccw_int_handler(struct ccw_device
*cdev,
vcdev->err = -EIO;
}
virtio_ccw_check_activity(vcdev, activity);
+#ifdef CONFIG_VIRTIO_HARDEN_NOTIFICATION
/* 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 +1148,9 @@ 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..96ec56d44b91 100644
--- a/drivers/virtio/Kconfig
+++ b/drivers/virtio/Kconfig
@@ -35,6 +35,17 @@ menuconfig VIRTIO_MENU
if VIRTIO_MENU
+config VIRTIO_HARDEN_NOTIFICATION
+ bool "Harden virtio notification"
+ help
+ Enable this to harden the device notifications and supress
+ the ones that are illegal.
+
+ Experimental: not all drivers handle this correctly at this
+ point.
+
+ 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
Cornelia Huck
2022-Jun-21 09:16 UTC
[PATCH V2] virtio: disable notification hardening by default
On Mon, Jun 20 2022, Jason Wang <jasowang at redhat.com> 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 at redhat.com> > --- > Changes since V1: > - tweak the Kconfig prompt > - don't hold spinlock for IRQ path in s390 > --- > drivers/s390/virtio/virtio_ccw.c | 4 ++++ > drivers/virtio/Kconfig | 11 +++++++++++ > drivers/virtio/virtio.c | 2 ++ > drivers/virtio/virtio_ring.c | 12 ++++++++++++ > include/linux/virtio_config.h | 2 ++ > 5 files changed, 31 insertions(+) > > diff --git a/drivers/s390/virtio/virtio_ccw.c b/drivers/s390/virtio/virtio_ccw.c > index 97e51c34e6cf..89bbf7ccfdd1 100644 > --- a/drivers/s390/virtio/virtio_ccw.c > +++ b/drivers/s390/virtio/virtio_ccw.c > @@ -1136,8 +1136,10 @@ static void virtio_ccw_int_handler(struct ccw_device *cdev, > vcdev->err = -EIO; > } > virtio_ccw_check_activity(vcdev, activity); > +#ifdef CONFIG_VIRTIO_HARDEN_NOTIFICATION > /* Interrupts are disabled here */ > read_lock(&vcdev->irq_lock);Should we add a comment that this pairs with virtio_ccw_synchronize_cbs()? Just to avoid future headscratching as to why this lock is only needed when notification hardening is enabled.> +#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 +1148,9 @@ 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..96ec56d44b91 100644 > --- a/drivers/virtio/Kconfig > +++ b/drivers/virtio/Kconfig > @@ -35,6 +35,17 @@ menuconfig VIRTIO_MENU > > if VIRTIO_MENU > > +config VIRTIO_HARDEN_NOTIFICATION > + bool "Harden virtio notification" > + help > + Enable this to harden the device notifications and supress > + the ones that are illegal."...and suppress those that happen at a time where notifications are illegal." ?> + > + Experimental: not all drivers handle this correctly at this > + point."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." Or is that too verbose?> + > + If unsure, say N. > + > config VIRTIO_PCI > tristate "PCI driver for virtio devices" > depends on PCIThe ifdeffery looks a big ugly, but I don't have a better idea.