CVE-2024-46683

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

drm/xe: prevent UAF around preempt fence

The fence lock is part of the queue, therefore in the current design

anything locking the fence should then also hold a ref to the queue to

prevent the queue from being freed.

However, currently it looks like we signal the fence and then drop the

queue ref, but if something is waiting on the fence, the waiter is

kicked to wake up at some later point, where upon waking up it first

grabs the lock before checking the fence state. But if we have already

dropped the queue ref, then the lock might already be freed as part of

the queue, leading to uaf.

To prevent this, move the fence lock into the fence itself so we don't

run into lifetime issues. Alternative might be to have device level

lock, or only release the queue in the fence release callback, however

that might require pushing to another worker to avoid locking issues.

References: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/2454

References: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/2342

References: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/2020

(cherry picked from commit 7116c35aacedc38be6d15bd21b2fc936eed0008b)