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

[Xu Zaibo]

Hi Zhangfei,


On 2020/2/24 15:06, Zhangfei Gao wrote:
> When uacce parent device module is removed, user app may
> still keep the mmaped area, which can be accessed unsafely.
> When rmmod, Parent device drvier 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>
> ---
>   drivers/misc/uacce/uacce.c | 17 +++++++++++++++++
>   include/linux/uacce.h      |  2 ++
>   2 files changed, 19 insertions(+)
>
> diff --git a/drivers/misc/uacce/uacce.c b/drivers/misc/uacce/uacce.c
> index ffced4d..1bcc5e6 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,
>   };
>   
> @@ -585,6 +595,13 @@ void uacce_remove(struct uacce_device *uacce)
>   		cdev_device_del(uacce->cdev, &uacce->dev);
>   	xa_erase(&uacce_xa, uacce->dev_id);
>   	put_device(&uacce->dev);
> +
> +	/*
> +	 * unmap remainning 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);
Should we unmap them at the first of 'uacce_remove',  and before 
'uacce_put_queue'?

Thanks,
Zaibo

.
>   }
>   EXPORT_SYMBOL_GPL(uacce_remove);
>   
> 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;
>   };
>   
>   /**