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Subject[PATCH v2 2/2] uacce: Handle parent device removal
Date
From: Jean-Philippe Brucker <jean-philippe@linaro.org>

The uacce driver must deal with a possible removal of the parent device
at any time. Although uacce_remove(), called on device removal and on
driver unbind, prevents future use of the uacce fops by removing the
cdev, fops that were called before that point may still be running.

Serialize uacce_fops_open() and uacce_remove() with uacce->mutex.
Serialize other fops against uacce_remove() with q->mutex.
Since we need to protect uacce_fops_poll() which gets called on the fast
path, replace uacce->queues_lock with q->mutex to improve scalability.
The other fops are only used during setup.

uacce_queue_is_valid(), checked under q->mutex or uacce_mutex, denotes
whether uacce_remove() has disabled all queues. If that is the case,
don't go any further since the parent device is being removed and
uacce->ops should not be called anymore.

Signed-off-by: Zhangfei Gao <zhangfei.gao@linaro.org>
Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
---
drivers/misc/uacce/uacce.c | 133 ++++++++++++++++++++++++-------------
include/linux/uacce.h | 6 +-
2 files changed, 91 insertions(+), 48 deletions(-)

diff --git a/drivers/misc/uacce/uacce.c b/drivers/misc/uacce/uacce.c
index f82f2dd30e76..1a963f96639c 100644
--- a/drivers/misc/uacce/uacce.c
+++ b/drivers/misc/uacce/uacce.c
@@ -9,43 +9,38 @@

static struct class *uacce_class;
static dev_t uacce_devt;
-static DEFINE_MUTEX(uacce_mutex);
static DEFINE_XARRAY_ALLOC(uacce_xa);

-static int uacce_start_queue(struct uacce_queue *q)
+/*
+ * If the parent driver or the device disappears, the queue state is invalid and
+ * ops are not usable anymore.
+ */
+static bool uacce_queue_is_valid(struct uacce_queue *q)
{
- int ret = 0;
+ return q->state == UACCE_Q_INIT || q->state == UACCE_Q_STARTED;
+}

- mutex_lock(&uacce_mutex);
+static int uacce_start_queue(struct uacce_queue *q)
+{
+ int ret;

- if (q->state != UACCE_Q_INIT) {
- ret = -EINVAL;
- goto out_with_lock;
- }
+ if (q->state != UACCE_Q_INIT)
+ return -EINVAL;

if (q->uacce->ops->start_queue) {
ret = q->uacce->ops->start_queue(q);
if (ret < 0)
- goto out_with_lock;
+ return ret;
}

q->state = UACCE_Q_STARTED;
-
-out_with_lock:
- mutex_unlock(&uacce_mutex);
-
- return ret;
+ return 0;
}

static int uacce_put_queue(struct uacce_queue *q)
{
struct uacce_device *uacce = q->uacce;

- mutex_lock(&uacce_mutex);
-
- if (q->state == UACCE_Q_ZOMBIE)
- goto out;
-
if ((q->state == UACCE_Q_STARTED) && uacce->ops->stop_queue)
uacce->ops->stop_queue(q);

@@ -54,8 +49,6 @@ static int uacce_put_queue(struct uacce_queue *q)
uacce->ops->put_queue(q);

q->state = UACCE_Q_ZOMBIE;
-out:
- mutex_unlock(&uacce_mutex);

return 0;
}
@@ -65,20 +58,36 @@ static long uacce_fops_unl_ioctl(struct file *filep,
{
struct uacce_queue *q = filep->private_data;
struct uacce_device *uacce = q->uacce;
+ long ret = -ENXIO;
+
+ /*
+ * uacce->ops->ioctl() may take the mmap_lock when copying arg to/from
+ * user. Avoid a circular lock dependency with uacce_fops_mmap(), which
+ * gets called with mmap_lock held, by taking uacce->mutex instead of
+ * q->mutex. Doing this in uacce_fops_mmap() is not possible because
+ * uacce_fops_open() calls iommu_sva_bind_device(), which takes
+ * mmap_lock, while holding uacce->mutex.
+ */
+ mutex_lock(&uacce->mutex);
+ if (!uacce_queue_is_valid(q))
+ goto out_unlock;

switch (cmd) {
case UACCE_CMD_START_Q:
- return uacce_start_queue(q);
-
+ ret = uacce_start_queue(q);
+ break;
case UACCE_CMD_PUT_Q:
- return uacce_put_queue(q);
-
+ ret = uacce_put_queue(q);
+ break;
default:
- if (!uacce->ops->ioctl)
- return -EINVAL;
-
- return uacce->ops->ioctl(q, cmd, arg);
+ if (uacce->ops->ioctl)
+ ret = uacce->ops->ioctl(q, cmd, arg);
+ else
+ ret = -EINVAL;
}
+out_unlock:
+ mutex_unlock(&uacce->mutex);
+ return ret;
}

#ifdef CONFIG_COMPAT
@@ -136,6 +145,13 @@ static int uacce_fops_open(struct inode *inode, struct file *filep)
if (!q)
return -ENOMEM;

+ mutex_lock(&uacce->mutex);
+
+ if (!uacce->parent) {
+ ret = -EINVAL;
+ goto out_with_mem;
+ }
+
ret = uacce_bind_queue(uacce, q);
if (ret)
goto out_with_mem;
@@ -152,10 +168,9 @@ static int uacce_fops_open(struct inode *inode, struct file *filep)
filep->private_data = q;
uacce->inode = inode;
q->state = UACCE_Q_INIT;
-
- mutex_lock(&uacce->queues_lock);
+ mutex_init(&q->mutex);
list_add(&q->list, &uacce->queues);
- mutex_unlock(&uacce->queues_lock);
+ mutex_unlock(&uacce->mutex);

return 0;

@@ -163,18 +178,20 @@ static int uacce_fops_open(struct inode *inode, struct file *filep)
uacce_unbind_queue(q);
out_with_mem:
kfree(q);
+ mutex_unlock(&uacce->mutex);
return ret;
}

static int uacce_fops_release(struct inode *inode, struct file *filep)
{
struct uacce_queue *q = filep->private_data;
+ struct uacce_device *uacce = q->uacce;

- mutex_lock(&q->uacce->queues_lock);
- list_del(&q->list);
- mutex_unlock(&q->uacce->queues_lock);
+ mutex_lock(&uacce->mutex);
uacce_put_queue(q);
uacce_unbind_queue(q);
+ list_del(&q->list);
+ mutex_unlock(&uacce->mutex);
kfree(q);

return 0;
@@ -217,10 +234,9 @@ static int uacce_fops_mmap(struct file *filep, struct vm_area_struct *vma)
vma->vm_private_data = q;
qfr->type = type;

- mutex_lock(&uacce_mutex);
-
- if (q->state != UACCE_Q_INIT && q->state != UACCE_Q_STARTED) {
- ret = -EINVAL;
+ mutex_lock(&q->mutex);
+ if (!uacce_queue_is_valid(q)) {
+ ret = -ENXIO;
goto out_with_lock;
}

@@ -248,12 +264,12 @@ static int uacce_fops_mmap(struct file *filep, struct vm_area_struct *vma)
}

q->qfrs[type] = qfr;
- mutex_unlock(&uacce_mutex);
+ mutex_unlock(&q->mutex);

return ret;

out_with_lock:
- mutex_unlock(&uacce_mutex);
+ mutex_unlock(&q->mutex);
kfree(qfr);
return ret;
}
@@ -262,12 +278,20 @@ static __poll_t uacce_fops_poll(struct file *file, poll_table *wait)
{
struct uacce_queue *q = file->private_data;
struct uacce_device *uacce = q->uacce;
+ __poll_t ret = 0;
+
+ mutex_lock(&q->mutex);
+ if (!uacce_queue_is_valid(q))
+ goto out_unlock;

poll_wait(file, &q->wait, wait);
+
if (uacce->ops->is_q_updated && uacce->ops->is_q_updated(q))
- return EPOLLIN | EPOLLRDNORM;
+ ret = EPOLLIN | EPOLLRDNORM;

- return 0;
+out_unlock:
+ mutex_unlock(&q->mutex);
+ return ret;
}

static const struct file_operations uacce_fops = {
@@ -450,7 +474,7 @@ struct uacce_device *uacce_alloc(struct device *parent,
goto err_with_uacce;

INIT_LIST_HEAD(&uacce->queues);
- mutex_init(&uacce->queues_lock);
+ mutex_init(&uacce->mutex);
device_initialize(&uacce->dev);
uacce->dev.devt = MKDEV(MAJOR(uacce_devt), uacce->dev_id);
uacce->dev.class = uacce_class;
@@ -507,13 +531,23 @@ void uacce_remove(struct uacce_device *uacce)
if (uacce->inode)
unmap_mapping_range(uacce->inode->i_mapping, 0, 0, 1);

+ /*
+ * uacce_fops_open() may be running concurrently, even after we remove
+ * the cdev. Holding uacce->mutex ensures that open() does not obtain a
+ * removed uacce device.
+ */
+ mutex_lock(&uacce->mutex);
/* ensure no open queue remains */
- mutex_lock(&uacce->queues_lock);
list_for_each_entry_safe(q, next_q, &uacce->queues, list) {
+ /*
+ * Taking q->mutex ensures that fops do not use the defunct
+ * uacce->ops after the queue is disabled.
+ */
+ mutex_lock(&q->mutex);
uacce_put_queue(q);
+ mutex_unlock(&q->mutex);
uacce_unbind_queue(q);
}
- mutex_unlock(&uacce->queues_lock);

/* disable sva now since no opened queues */
uacce_disable_sva(uacce);
@@ -521,6 +555,13 @@ void uacce_remove(struct uacce_device *uacce)
if (uacce->cdev)
cdev_device_del(uacce->cdev, &uacce->dev);
xa_erase(&uacce_xa, uacce->dev_id);
+ /*
+ * uacce exists as long as there are open fds, but ops will be freed
+ * now. Ensure that bugs cause NULL deref rather than use-after-free.
+ */
+ uacce->ops = NULL;
+ uacce->parent = NULL;
+ mutex_unlock(&uacce->mutex);
put_device(&uacce->dev);
}
EXPORT_SYMBOL_GPL(uacce_remove);
diff --git a/include/linux/uacce.h b/include/linux/uacce.h
index 48e319f40275..9ce88c28b0a8 100644
--- a/include/linux/uacce.h
+++ b/include/linux/uacce.h
@@ -70,6 +70,7 @@ enum uacce_q_state {
* @wait: wait queue head
* @list: index into uacce queues list
* @qfrs: pointer of qfr regions
+ * @mutex: protects queue state
* @state: queue state machine
* @pasid: pasid associated to the mm
* @handle: iommu_sva handle returned by iommu_sva_bind_device()
@@ -80,6 +81,7 @@ struct uacce_queue {
wait_queue_head_t wait;
struct list_head list;
struct uacce_qfile_region *qfrs[UACCE_MAX_REGION];
+ struct mutex mutex;
enum uacce_q_state state;
u32 pasid;
struct iommu_sva *handle;
@@ -97,9 +99,9 @@ struct uacce_queue {
* @dev_id: id of the uacce device
* @cdev: cdev of the uacce
* @dev: dev of the uacce
+ * @mutex: protects uacce operation
* @priv: private pointer of the uacce
* @queues: list of queues
- * @queues_lock: lock for queues list
* @inode: core vfs
*/
struct uacce_device {
@@ -113,9 +115,9 @@ struct uacce_device {
u32 dev_id;
struct cdev *cdev;
struct device dev;
+ struct mutex mutex;
void *priv;
struct list_head queues;
- struct mutex queues_lock;
struct inode *inode;
};

--
2.36.1
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