virtio: acknowledge all features before access
commit 4fa59ede95195f267101a1b8916992cf3f245cdb upstream.
The feature negotiation was designed in a way that
makes it possible for devices to know which config
fields will be accessed by drivers.
This is broken since commit 404123c2db79 ("virtio: allow drivers to
validate features") with fallout in at least block and net. We have a
partial work-around in commit 2f9a174f918e ("virtio: write back
F_VERSION_1 before validate") which at least lets devices find out which
format should config space have, but this is a partial fix: guests
should not access config space without acknowledging features since
otherwise we'll never be able to change the config space format.
To fix, split finalize_features from virtio_finalize_features and
call finalize_features with all feature bits before validation,
and then - if validation changed any bits - once again after.
Since virtio_finalize_features no longer writes out features
rename it to virtio_features_ok - since that is what it does:
checks that features are ok with the device.
As a side effect, this also reduces the amount of hypervisor accesses -
we now only acknowledge features once unless we are clearing any
features when validating (which is uncommon).
IRC I think that this was more or less always the intent in the spec but
unfortunately the way the spec is worded does not say this explicitly, I
plan to address this at the spec level, too.
Acked-by: Jason Wang <jasowang@redhat.com>
Cc: stable@vger.kernel.org
Fixes: 404123c2db79 ("virtio: allow drivers to validate features")
Fixes: 2f9a174f918e ("virtio: write back F_VERSION_1 before validate")
Cc: "Halil Pasic" <pasic@linux.ibm.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
index ae092fc..441bc05 100644
--- a/drivers/virtio/virtio.c
+++ b/drivers/virtio/virtio.c
@@ -167,14 +167,13 @@
}
EXPORT_SYMBOL_GPL(virtio_add_status);
-static int virtio_finalize_features(struct virtio_device *dev)
+/* Do some validation, then set FEATURES_OK */
+static int virtio_features_ok(struct virtio_device *dev)
{
- int ret = dev->config->finalize_features(dev);
unsigned status;
+ int ret;
might_sleep();
- if (ret)
- return ret;
ret = arch_has_restricted_virtio_memory_access();
if (ret) {
@@ -239,17 +238,6 @@
driver_features_legacy = driver_features;
}
- /*
- * Some devices detect legacy solely via F_VERSION_1. Write
- * F_VERSION_1 to force LE config space accesses before FEATURES_OK for
- * these when needed.
- */
- if (drv->validate && !virtio_legacy_is_little_endian()
- && device_features & BIT_ULL(VIRTIO_F_VERSION_1)) {
- dev->features = BIT_ULL(VIRTIO_F_VERSION_1);
- dev->config->finalize_features(dev);
- }
-
if (device_features & (1ULL << VIRTIO_F_VERSION_1))
dev->features = driver_features & device_features;
else
@@ -260,13 +248,26 @@
if (device_features & (1ULL << i))
__virtio_set_bit(dev, i);
+ err = dev->config->finalize_features(dev);
+ if (err)
+ goto err;
+
if (drv->validate) {
+ u64 features = dev->features;
+
err = drv->validate(dev);
if (err)
goto err;
+
+ /* Did validation change any features? Then write them again. */
+ if (features != dev->features) {
+ err = dev->config->finalize_features(dev);
+ if (err)
+ goto err;
+ }
}
- err = virtio_finalize_features(dev);
+ err = virtio_features_ok(dev);
if (err)
goto err;
@@ -437,7 +438,11 @@
/* We have a driver! */
virtio_add_status(dev, VIRTIO_CONFIG_S_DRIVER);
- ret = virtio_finalize_features(dev);
+ ret = dev->config->finalize_features(dev);
+ if (ret)
+ goto err;
+
+ ret = virtio_features_ok(dev);
if (ret)
goto err;
diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h
index 8519b3a..b341dd6 100644
--- a/include/linux/virtio_config.h
+++ b/include/linux/virtio_config.h
@@ -62,8 +62,9 @@
* Returns the first 64 feature bits (all we currently need).
* @finalize_features: confirm what device features we'll be using.
* vdev: the virtio_device
- * This gives the final feature bits for the device: it can change
+ * This sends the driver feature bits to the device: it can change
* the dev->feature bits if it wants.
+ * Note: despite the name this can be called any number of times.
* Returns 0 on success or error status
* @bus_name: return the bus name associated with the device (optional)
* vdev: the virtio_device
