Re: [PATCH v3 1/2] drm/xe: Limit num_syncs to prevent oversized allocations

[Matthew Brost <matthew.brost@intel.com>]

On Fri, Dec 05, 2025 at 11:47:17PM +0000, Shuicheng Lin wrote:
> The exec and vm_bind ioctl allow userspace to specify an arbitrary
> num_syncs value. Without bounds checking, a very large num_syncs
> can force an excessively large allocation, leading to kernel warnings
> from the page allocator as below.
> 
> Introduce DRM_XE_MAX_SYNCS (set to 1024) and reject any request
> exceeding this limit.
> 
> "
> ------------[ cut here ]------------
> WARNING: CPU: 0 PID: 1217 at mm/page_alloc.c:5124 __alloc_frozen_pages_noprof+0x2f8/0x2180 mm/page_alloc.c:5124
> ...
> Call Trace:
>  <TASK>
>  alloc_pages_mpol+0xe4/0x330 mm/mempolicy.c:2416
>  ___kmalloc_large_node+0xd8/0x110 mm/slub.c:4317
>  __kmalloc_large_node_noprof+0x18/0xe0 mm/slub.c:4348
>  __do_kmalloc_node mm/slub.c:4364 [inline]
>  __kmalloc_noprof+0x3d4/0x4b0 mm/slub.c:4388
>  kmalloc_noprof include/linux/slab.h:909 [inline]
>  kmalloc_array_noprof include/linux/slab.h:948 [inline]
>  xe_exec_ioctl+0xa47/0x1e70 drivers/gpu/drm/xe/xe_exec.c:158
>  drm_ioctl_kernel+0x1f1/0x3e0 drivers/gpu/drm/drm_ioctl.c:797
>  drm_ioctl+0x5e7/0xc50 drivers/gpu/drm/drm_ioctl.c:894
>  xe_drm_ioctl+0x10b/0x170 drivers/gpu/drm/xe/xe_device.c:224
>  vfs_ioctl fs/ioctl.c:51 [inline]
>  __do_sys_ioctl fs/ioctl.c:598 [inline]
>  __se_sys_ioctl fs/ioctl.c:584 [inline]
>  __x64_sys_ioctl+0x18b/0x210 fs/ioctl.c:584
>  do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>  do_syscall_64+0xbb/0x380 arch/x86/entry/syscall_64.c:94
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> ...
> "
> 
> v2: Add "Reported-by" and Cc stable kernels.
> v3: Change XE_MAX_SYNCS from 64 to 1024. (Matt & Ashutosh)
> v4: s/XE_MAX_SYNCS/DRM_XE_MAX_SYNCS/ (Matt)
> v5: Do the check at the top of the exec func. (Matt)
> 
> Fixes: dd08ebf6c352 ("drm/xe: Introduce a new DRM driver for Intel GPUs")
> Reported-by: Koen Koning <koen.koning@intel.com>
> Reported-by: Peter Senna Tschudin <peter.senna@linux.intel.com>
> Closes: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/6450
> Cc: <stable@vger.kernel.org> # v6.12+
> Cc: Matthew Brost <matthew.brost@intel.com>

Reviewed-by: Matthew Brost <matthew.brost@intel.com>

> Cc: Michal Mrozek <michal.mrozek@intel.com>
> Cc: Carl Zhang <carl.zhang@intel.com>
> Cc: José Roberto de Souza <jose.souza@intel.com>
> Cc: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
> Cc: Ivan Briano <ivan.briano@intel.com>
> Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
> Cc: Ashutosh Dixit <ashutosh.dixit@intel.com>
> Signed-off-by: Shuicheng Lin <shuicheng.lin@intel.com>
> ---
>  drivers/gpu/drm/xe/xe_exec.c | 3 ++-
>  drivers/gpu/drm/xe/xe_vm.c   | 3 +++
>  include/uapi/drm/xe_drm.h    | 1 +
>  3 files changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_exec.c b/drivers/gpu/drm/xe/xe_exec.c
> index 4d81210e41f5..fd9480031750 100644
> --- a/drivers/gpu/drm/xe/xe_exec.c
> +++ b/drivers/gpu/drm/xe/xe_exec.c
> @@ -132,7 +132,8 @@ int xe_exec_ioctl(struct drm_device *dev, void *data, struct drm_file *file)
>  
>  	if (XE_IOCTL_DBG(xe, args->extensions) ||
>  	    XE_IOCTL_DBG(xe, args->pad[0] || args->pad[1] || args->pad[2]) ||
> -	    XE_IOCTL_DBG(xe, args->reserved[0] || args->reserved[1]))
> +	    XE_IOCTL_DBG(xe, args->reserved[0] || args->reserved[1]) ||
> +	    XE_IOCTL_DBG(xe, args->num_syncs > DRM_XE_MAX_SYNCS))
>  		return -EINVAL;
>  
>  	q = xe_exec_queue_lookup(xef, args->exec_queue_id);
> diff --git a/drivers/gpu/drm/xe/xe_vm.c b/drivers/gpu/drm/xe/xe_vm.c
> index c2012d20faa6..24eced1d970c 100644
> --- a/drivers/gpu/drm/xe/xe_vm.c
> +++ b/drivers/gpu/drm/xe/xe_vm.c
> @@ -3341,6 +3341,9 @@ static int vm_bind_ioctl_check_args(struct xe_device *xe, struct xe_vm *vm,
>  	if (XE_IOCTL_DBG(xe, args->extensions))
>  		return -EINVAL;
>  
> +	if (XE_IOCTL_DBG(xe, args->num_syncs > DRM_XE_MAX_SYNCS))
> +		return -EINVAL;
> +
>  	if (args->num_binds > 1) {
>  		u64 __user *bind_user =
>  			u64_to_user_ptr(args->vector_of_binds);
> diff --git a/include/uapi/drm/xe_drm.h b/include/uapi/drm/xe_drm.h
> index 876a076fa6c0..f7f3573b8d6f 100644
> --- a/include/uapi/drm/xe_drm.h
> +++ b/include/uapi/drm/xe_drm.h
> @@ -1484,6 +1484,7 @@ struct drm_xe_exec {
>  	/** @exec_queue_id: Exec queue ID for the batch buffer */
>  	__u32 exec_queue_id;
>  
> +#define DRM_XE_MAX_SYNCS 1024
>  	/** @num_syncs: Amount of struct drm_xe_sync in array. */
>  	__u32 num_syncs;
>  
> -- 
> 2.50.1
>