drm/xe: Wait on external BO kernel fences in exec IOCTL

Overview

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

drm/xe: Wait on external BO kernel fences in exec IOCTL

Before arming a user job, xe_exec_ioctl() only added the VM's dma-resv KERNEL slot as a dependency. That slot covers rebinds and the kernel operations of the VM's private BOs, but not external BOs (bo->vm == NULL), which carry their kernel operations (evictions, moves, ...) in their own dma-resv KERNEL slot.

The DMA_RESV_USAGE_KERNEL slot is the cross-driver contract for memory management operations that must complete before the BO or its backing store may be used: any accessor is required to wait on the KERNEL fences before touching the resv. By skipping the external BOs' KERNEL slots, the exec path violated that contract and could schedule a user job while a kernel operation on an external BO mapped by the VM was still in flight, racing against it and potentially reading or writing memory that was being moved.

Replace the VM-only dependency with an iteration over every object locked by the exec, adding each object's KERNEL slot as a job dependency. This covers the VM resv (rebinds and private BOs) as well as every external BO, mirroring the drm_gpuvm_resv_add_fence() call that later publishes the job fence to the same set of objects. Long-running mode continues to skip this, as before.

(cherry picked from commit a6b842acf3ddd1efc53a56de9260cfa718fb35e7)

Affected

• Linux >= dd08ebf6c3525a7ea2186e636df064ea47281987 < 1738db550334adca0e7fcf0ef684198fb7462779
• Linux >= dd08ebf6c3525a7ea2186e636df064ea47281987 < 21976fe5258494ac38b63d103be81bf1180ae4ae
• Linux >= dd08ebf6c3525a7ea2186e636df064ea47281987 < 5d363d00bc9799b90a0dc89eb1c5dcb909c042ee
• Linux >= dd08ebf6c3525a7ea2186e636df064ea47281987 < af80e2bfde9312c76b60cf9274248dce0410b30d
• Linux 6.8

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.