drm/xe: Limit num_syncs to prevent oversized allocations

In the Linux kernel, the following vulnerability has been resolved:

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)

(cherry picked from commit b07bac9bd708ec468cd1b8a5fe70ae2ac9b0a11c)