drm/xe: Make dma-fences compliant with the safe access rules

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: drm/xe: Make dma-fences compliant with the safe access rules Xe can free some of the data pointed to by the dma-fences it exports. Most notably the timeline name can get freed if userspace closes the associated submit queue. At the same time the fence could have been exported to a third party (for example a sync_fence fd) which will then cause an use- after-free on subsequent access. To make this safe we need to make the driver compliant with the newly documented dma-fence rules. Driver has to ensure a RCU grace period between signalling a fence and freeing any data pointed to by said fence. For the timeline name we simply make the queue be freed via kfree_rcu and for the shared lock associated with multiple queues we add a RCU grace period before freeing the per GT structure holding the lock.

References

• https://git.kernel.org/stable/c/b17fcce70733c211cb5dabf54f4f9491920b1d92
• https://git.kernel.org/stable/c/ba37807d08bae67de6139346a85650cab5f6145a
• https://git.kernel.org/stable/c/683b0e397dad9f26a42dcacf6f7f545a77ce6c06
• https://git.kernel.org/stable/c/6bd90e700b4285e6a7541e00f969cab0d696adde