[PATCH 0/2] Protect against iommu driver disconnect

[PATCH 0/2] Protect against iommu driver disconnect

[Alex Williamson]

Michael Tsirkin pointed out that file operations on /dev/vfio/vfio
dereference iommu_driver and iommu_data without a lock.  If releasing
a group or unsetting the container occurs concurrently, we could race.
We currently use a mutex when setting this association, so we can
convert to a rwsem keeping the existing mutex critical sections as
down_writes and add down_reads where these are used.  Thanks,

Alex

---

Alex Williamson (2):
      vfio: Convert container->group_lock to rwsem
      vfio: Use down_reads to protect iommu disconnects


 drivers/vfio/vfio.c |   83 +++++++++++++++++++++++++++++++++++----------------
 1 file changed, 57 insertions(+), 26 deletions(-)

[PATCH 1/2] vfio: Convert container->group_lock to rwsem

[Alex Williamson]

All current users are writers, maintaining current mutual exclusion.
This lets us add read users next.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
---
 drivers/vfio/vfio.c |   21 +++++++++++----------
 1 file changed, 11 insertions(+), 10 deletions(-)

diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
index 21eddd9..073788e 100644
--- a/drivers/vfio/vfio.c
+++ b/drivers/vfio/vfio.c
@@ -24,6 +24,7 @@
 #include <linux/list.h>
 #include <linux/module.h>
 #include <linux/mutex.h>
+#include <linux/rwsem.h>
 #include <linux/sched.h>
 #include <linux/slab.h>
 #include <linux/string.h>
@@ -57,7 +58,7 @@ struct vfio_iommu_driver {
 struct vfio_container {
 	struct kref			kref;
 	struct list_head		group_list;
-	struct mutex			group_lock;
+	struct rw_semaphore		group_lock;
 	struct vfio_iommu_driver	*iommu_driver;
 	void				*iommu_data;
 };
@@ -738,7 +739,7 @@ static long vfio_ioctl_check_extension(struct vfio_container *container,
 	return ret;
 }
 
-/* hold container->group_lock */
+/* hold write lock on container->group_lock */
 static int __vfio_container_attach_groups(struct vfio_container *container,
 					  struct vfio_iommu_driver *driver,
 					  void *data)
@@ -769,7 +770,7 @@ static long vfio_ioctl_set_iommu(struct vfio_container *container,
 	struct vfio_iommu_driver *driver;
 	long ret = -ENODEV;
 
-	mutex_lock(&container->group_lock);
+	down_write(&container->group_lock);
 
 	/*
 	 * The container is designed to be an unprivileged interface while
@@ -780,7 +781,7 @@ static long vfio_ioctl_set_iommu(struct vfio_container *container,
 	 * the container is deprivileged and returns to an unset state.
 	 */
 	if (list_empty(&container->group_list) || container->iommu_driver) {
-		mutex_unlock(&container->group_lock);
+		up_write(&container->group_lock);
 		return -EINVAL;
 	}
 
@@ -827,7 +828,7 @@ static long vfio_ioctl_set_iommu(struct vfio_container *container,
 
 	mutex_unlock(&vfio.iommu_drivers_lock);
 skip_drivers_unlock:
-	mutex_unlock(&container->group_lock);
+	up_write(&container->group_lock);
 
 	return ret;
 }
@@ -882,7 +883,7 @@ static int vfio_fops_open(struct inode *inode, struct file *filep)
 		return -ENOMEM;
 
 	INIT_LIST_HEAD(&container->group_list);
-	mutex_init(&container->group_lock);
+	init_rwsem(&container->group_lock);
 	kref_init(&container->kref);
 
 	filep->private_data = container;
@@ -961,7 +962,7 @@ static void __vfio_group_unset_container(struct vfio_group *group)
 	struct vfio_container *container = group->container;
 	struct vfio_iommu_driver *driver;
 
-	mutex_lock(&container->group_lock);
+	down_write(&container->group_lock);
 
 	driver = container->iommu_driver;
 	if (driver)
@@ -979,7 +980,7 @@ static void __vfio_group_unset_container(struct vfio_group *group)
 		container->iommu_data = NULL;
 	}
 
-	mutex_unlock(&container->group_lock);
+	up_write(&container->group_lock);
 
 	vfio_container_put(container);
 }
@@ -1039,7 +1040,7 @@ static int vfio_group_set_container(struct vfio_group *group, int container_fd)
 	container = f.file->private_data;
 	WARN_ON(!container); /* fget ensures we don't race vfio_release */
 
-	mutex_lock(&container->group_lock);
+	down_write(&container->group_lock);
 
 	driver = container->iommu_driver;
 	if (driver) {
@@ -1057,7 +1058,7 @@ static int vfio_group_set_container(struct vfio_group *group, int container_fd)
 	atomic_inc(&group->container_users);
 
 unlock_out:
-	mutex_unlock(&container->group_lock);
+	up_write(&container->group_lock);
 	fdput(f);
 	return ret;
 }

[PATCH 2/2] vfio: Use down_reads to protect iommu disconnects

[Alex Williamson]

If a group or device is released or a container is unset from a group
it can race against file ops on the container.  Protect these with
down_reads to allow concurrent users.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Reported-by: Michael S. Tsirkin <mst@redhat.com>
---
 drivers/vfio/vfio.c |   62 ++++++++++++++++++++++++++++++++++++++-------------
 1 file changed, 46 insertions(+), 16 deletions(-)

diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
index 073788e..ac7423b 100644
--- a/drivers/vfio/vfio.c
+++ b/drivers/vfio/vfio.c
@@ -704,9 +704,13 @@ EXPORT_SYMBOL_GPL(vfio_del_group_dev);
 static long vfio_ioctl_check_extension(struct vfio_container *container,
 				       unsigned long arg)
 {
-	struct vfio_iommu_driver *driver = container->iommu_driver;
+	struct vfio_iommu_driver *driver;
 	long ret = 0;
 
+	down_read(&container->group_lock);
+
+	driver = container->iommu_driver;
+
 	switch (arg) {
 		/* No base extensions yet */
 	default:
@@ -736,6 +740,8 @@ static long vfio_ioctl_check_extension(struct vfio_container *container,
 						 VFIO_CHECK_EXTENSION, arg);
 	}
 
+	up_read(&container->group_lock);
+
 	return ret;
 }
 
@@ -844,9 +850,6 @@ static long vfio_fops_unl_ioctl(struct file *filep,
 	if (!container)
 		return ret;
 
-	driver = container->iommu_driver;
-	data = container->iommu_data;
-
 	switch (cmd) {
 	case VFIO_GET_API_VERSION:
 		ret = VFIO_API_VERSION;
@@ -858,8 +861,15 @@ static long vfio_fops_unl_ioctl(struct file *filep,
 		ret = vfio_ioctl_set_iommu(container, arg);
 		break;
 	default:
+		down_read(&container->group_lock);
+
+		driver = container->iommu_driver;
+		data = container->iommu_data;
+
 		if (driver) /* passthrough all unrecognized ioctls */
 			ret = driver->ops->ioctl(data, cmd, arg);
+
+		up_read(&container->group_lock);
 	}
 
 	return ret;
@@ -910,35 +920,55 @@ static ssize_t vfio_fops_read(struct file *filep, char __user *buf,
 			      size_t count, loff_t *ppos)
 {
 	struct vfio_container *container = filep->private_data;
-	struct vfio_iommu_driver *driver = container->iommu_driver;
+	struct vfio_iommu_driver *driver;
+	ssize_t ret = -EINVAL;
 
-	if (unlikely(!driver || !driver->ops->read))
-		return -EINVAL;
+	down_read(&container->group_lock);
+
+	driver = container->iommu_driver;
+	if (likely(driver && driver->ops->read))
+		ret = driver->ops->read(container->iommu_data,
+					buf, count, ppos);
 
-	return driver->ops->read(container->iommu_data, buf, count, ppos);
+	up_read(&container->group_lock);
+
+	return ret;
 }
 
 static ssize_t vfio_fops_write(struct file *filep, const char __user *buf,
 			       size_t count, loff_t *ppos)
 {
 	struct vfio_container *container = filep->private_data;
-	struct vfio_iommu_driver *driver = container->iommu_driver;
+	struct vfio_iommu_driver *driver;
+	ssize_t ret = -EINVAL;
 
-	if (unlikely(!driver || !driver->ops->write))
-		return -EINVAL;
+	down_read(&container->group_lock);
+
+	driver = container->iommu_driver;
+	if (likely(driver && driver->ops->write))
+		ret = driver->ops->write(container->iommu_data,
+					 buf, count, ppos);
+
+	up_read(&container->group_lock);
 
-	return driver->ops->write(container->iommu_data, buf, count, ppos);
+	return ret;
 }
 
 static int vfio_fops_mmap(struct file *filep, struct vm_area_struct *vma)
 {
 	struct vfio_container *container = filep->private_data;
-	struct vfio_iommu_driver *driver = container->iommu_driver;
+	struct vfio_iommu_driver *driver;
+	int ret = -EINVAL;
 
-	if (unlikely(!driver || !driver->ops->mmap))
-		return -EINVAL;
+	down_read(&container->group_lock);
 
-	return driver->ops->mmap(container->iommu_data, vma);
+	driver = container->iommu_driver;
+	if (likely(driver && driver->ops->mmap))
+		ret = driver->ops->mmap(container->iommu_data, vma);
+
+	up_read(&container->group_lock);
+
+	return ret;
 }
 
 static const struct file_operations vfio_fops = {