Medium [CVE-2026-68103] reject mapping a reserved doorbell to a new queue

In the Linux kernel, the following vulnerability has been resolved: drm/amdgpu: reject mapping a reserved doorbell to a new queue When creating an user-queue, the user space provides a doorbell BO handle and an offset within the bo to obtain a doorbell.

However current implementation using xa_store_irq() to store a doorbell, which allows a later queue created with the same BO and offset parameters to overwrite an existing queue and doorbell mapping.

This can cause problems like misrouting fence IRQ processing to a wrong queue, and mislead the cleanup process of one queue erasing the mapping of another queue.

This commit fixes this issue by replacing xa_store_irq with xa_insert_irq, which rejects mapping a reserved doorbell to a newly created queue (cherry picked from commit 6244eae22966350db52faf9c1369d3b2ffc5de4e) A local attacker could exploit a vulnerability where creating a user-queue with specific parameters overwrites an existing doorbell mapping.

This could lead to misrouting of interrupt requests (IRQs) and incorrect cleanup processes, potentially resulting in a denial of service. Userspace client with access to a supported AMDGPU device, on hardware/configuration using the relatively specialized User Mode Queue facility, can create conflicting user queues using the same doorbell mapping.