[PATCH v2] uacce: unmap remaining mmapping from user space

[Zhangfei Gao <zhangfei.gao@xxxxxxxxxx>]

When uacce parent device module is removed, user app may
still keep the mmaped area, which can be accessed unsafely.
When rmmod, Parent device driver will call uacce_remove,
which unmap all remaining mapping from user space for safety.
VM_FAULT_SIGBUS is also reported to user space accordingly.

Suggested-by: Dave Jiang <dave.jiang@xxxxxxxxx>
Signed-off-by: Zhangfei Gao <zhangfei.gao@xxxxxxxxxx>
---
 v2: Unmap before put_queue, where memory is freed, commented from Zaibo.

 drivers/misc/uacce/uacce.c | 16 ++++++++++++++++
 include/linux/uacce.h      |  2 ++
 2 files changed, 18 insertions(+)

diff --git a/drivers/misc/uacce/uacce.c b/drivers/misc/uacce/uacce.c
index ffced4d..d39307f 100644
--- a/drivers/misc/uacce/uacce.c
+++ b/drivers/misc/uacce/uacce.c
@@ -224,6 +224,7 @@ static int uacce_fops_open(struct inode *inode, struct file *filep)
 
 	init_waitqueue_head(&q->wait);
 	filep->private_data = q;
+	uacce->inode = inode;
 	q->state = UACCE_Q_INIT;
 
 	return 0;
@@ -253,6 +254,14 @@ static int uacce_fops_release(struct inode *inode, struct file *filep)
 	return 0;
 }
 
+static vm_fault_t uacce_vma_fault(struct vm_fault *vmf)
+{
+	if (vmf->flags & (FAULT_FLAG_MKWRITE | FAULT_FLAG_WRITE))
+		return VM_FAULT_SIGBUS;
+
+	return 0;
+}
+
 static void uacce_vma_close(struct vm_area_struct *vma)
 {
 	struct uacce_queue *q = vma->vm_private_data;
@@ -265,6 +274,7 @@ static void uacce_vma_close(struct vm_area_struct *vma)
 }
 
 static const struct vm_operations_struct uacce_vm_ops = {
+	.fault = uacce_vma_fault,
 	.close = uacce_vma_close,
 };
 
@@ -556,6 +566,12 @@ void uacce_remove(struct uacce_device *uacce)
 
 	if (!uacce)
 		return;
+	/*
+	 * unmap remaining mapping from user space, preventing user still
+	 * access the mmaped area while parent device is already removed
+	 */
+	if (uacce->inode)
+		unmap_mapping_range(uacce->inode->i_mapping, 0, 0, 1);
 
 	/* ensure no open queue remains */
 	mutex_lock(&uacce->mm_lock);
diff --git a/include/linux/uacce.h b/include/linux/uacce.h
index 904a461..0e215e6 100644
--- a/include/linux/uacce.h
+++ b/include/linux/uacce.h
@@ -98,6 +98,7 @@ struct uacce_queue {
  * @priv: private pointer of the uacce
  * @mm_list: list head of uacce_mm->list
  * @mm_lock: lock for mm_list
+ * @inode: core vfs
  */
 struct uacce_device {
 	const char *algs;
@@ -113,6 +114,7 @@ struct uacce_device {
 	void *priv;
 	struct list_head mm_list;
 	struct mutex mm_lock;
+	struct inode *inode;
 };
 
 /**
-- 
2.7.4