drm/xe: Limit num_syncs to prevent oversized allocations

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: dd08ebf ("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>
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>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Link: https://patch.msgid.link/20251205234715.2476561-5-shuicheng.lin@intel.com
(cherry picked from commit b07bac9)
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>

Author: ShuichengLin

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);

drivers/gpu/drm/xe/xe_vm.c

@@ -3324,6 +3324,9 @@ 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);

include/uapi/drm/xe_drm.h

@@ -1463,6 +1463,7 @@ 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;