Re: [PATCH v2 2/3] drm/xe: Validate user fence during creation

["Thomas Hellström" <thomas.hellstrom@linux.intel.com>]

On Thu, 2024-02-29 at 19:55 -0800, Matthew Brost wrote:
> Fail invalidate addresses during user fence creation.
> 
> Fixes: dd08ebf6c352 ("drm/xe: Introduce a new DRM driver for Intel
> GPUs")
> Signed-off-by: Matthew Brost <matthew.brost@intel.com>
> Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
> ---
>  drivers/gpu/drm/xe/xe_sync.c | 12 ++++++++----
>  1 file changed, 8 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_sync.c
> b/drivers/gpu/drm/xe/xe_sync.c
> index c836a5f3a1ea..c20e1f9ad267 100644
> --- a/drivers/gpu/drm/xe/xe_sync.c
> +++ b/drivers/gpu/drm/xe/xe_sync.c
> @@ -53,14 +53,18 @@ static struct xe_user_fence
> *user_fence_create(struct xe_device *xe, u64 addr,
>  					       u64 value)
>  {
>  	struct xe_user_fence *ufence;
> +	u64 __user *ptr = u64_to_user_ptr(addr);
> +
> +	if (!access_ok(ptr, sizeof(ptr)))
> +		return ERR_PTR(-EFAULT);

I think we also need to enforce u64 alignment. Otherwise, particularly
on 32-bit user-space the user fence memory could cross a page-border? 

>  
>  	ufence = kmalloc(sizeof(*ufence), GFP_KERNEL);
>  	if (!ufence)
> -		return NULL;
> +		return ERR_PTR(-ENOMEM);
>  
>  	ufence->xe = xe;
>  	kref_init(&ufence->refcount);
> -	ufence->addr = u64_to_user_ptr(addr);
> +	ufence->addr = ptr;
>  	ufence->value = value;
>  	ufence->mm = current->mm;
>  	mmgrab(ufence->mm);
> @@ -183,8 +187,8 @@ int xe_sync_entry_parse(struct xe_device *xe,
> struct xe_file *xef,
>  		} else {
>  			sync->ufence = user_fence_create(xe,
> sync_in.addr,
>  							
> sync_in.timeline_value);
> -			if (XE_IOCTL_DBG(xe, !sync->ufence))
> -				return -ENOMEM;
> +			if (XE_IOCTL_DBG(xe, IS_ERR(sync->ufence)))
> +				return PTR_ERR(sync->ufence);
>  		}
>  
>  		break;