Commit 01657bc1 authored by Robin Murphy's avatar Robin Murphy Committed by Joerg Roedel
Browse files

iommu: Avoid races around device probe 



We currently have 3 different ways that __iommu_probe_device() may be
called, but no real guarantee that multiple callers can't tread on each
other, especially once asynchronous driver probe gets involved. It would
likely have taken a fair bit of luck to hit this previously, but commit
57365a04 ("iommu: Move bus setup to IOMMU device registration") ups
the odds since now it's not just omap-iommu that may trigger multiple
bus_iommu_probe() calls in parallel if probing asynchronously.

Add a lock to ensure we can't try to double-probe a device, and also
close some possible race windows to make sure we're truly robust against
trying to double-initialise a group via two different member devices.

Reported-by: default avatarBrian Norris <briannorris@chromium.org>
Signed-off-by: default avatarRobin Murphy <robin.murphy@arm.com>
Tested-by: default avatarBrian Norris <briannorris@chromium.org>
Fixes: 57365a04 ("iommu: Move bus setup to IOMMU device registration")
Link: https://lore.kernel.org/r/1946ef9f774851732eed78760a78ec40dbc6d178.1667591503.git.robin.murphy@arm.com


Signed-off-by: default avatarJoerg Roedel <jroedel@suse.de>
parent 69e61ede

drivers/iommu/iommu.c

+22 −6
Original line number Diff line number Diff line
@@ -306,13 +306,23 @@ static int __iommu_probe_device(struct device *dev, struct list_head *group_list 
	const struct iommu_ops *ops = dev->bus->iommu_ops;

	struct iommu_device *iommu_dev;

	struct iommu_group *group;

	static DEFINE_MUTEX(iommu_probe_device_lock);

	int ret;



	if (!ops)

		return -ENODEV;



	if (!dev_iommu_get(dev))

		return -ENOMEM;

	/*

	 * Serialise to avoid races between IOMMU drivers registering in

	 * parallel and/or the "replay" calls from ACPI/OF code via client

	 * driver probe. Once the latter have been cleaned up we should

	 * probably be able to use device_lock() here to minimise the scope,

	 * but for now enforcing a simple global ordering is fine.

	 */

	mutex_lock(&iommu_probe_device_lock);

	if (!dev_iommu_get(dev)) {

		ret = -ENOMEM;

		goto err_unlock;

	}



	if (!try_module_get(ops->owner)) {

		ret = -EINVAL;
@@ -333,11 +343,14 @@ static int __iommu_probe_device(struct device *dev, struct list_head *group_list 
		ret = PTR_ERR(group);

		goto out_release;

	}

	iommu_group_put(group);



	mutex_lock(&group->mutex);

	if (group_list && !group->default_domain && list_empty(&group->entry))

		list_add_tail(&group->entry, group_list);

	mutex_unlock(&group->mutex);

	iommu_group_put(group);



	mutex_unlock(&iommu_probe_device_lock);

	iommu_device_link(iommu_dev, dev);



	return 0;
@@ -352,6 +365,9 @@ static int __iommu_probe_device(struct device *dev, struct list_head *group_list 
err_free:

	dev_iommu_free(dev);



err_unlock:

	mutex_unlock(&iommu_probe_device_lock);



	return ret;

}
@@ -1824,11 +1840,11 @@ int bus_iommu_probe(struct bus_type *bus) 
		return ret;



	list_for_each_entry_safe(group, next, &group_list, entry) {

		mutex_lock(&group->mutex);



		/* Remove item from the list */

		list_del_init(&group->entry);



		mutex_lock(&group->mutex);



		/* Try to allocate default domain */

		probe_alloc_default_domain(bus, group);