Bug 2420424 (CVE-2025-40340)

Summary: CVE-2025-40340 kernel: drm/xe: Fix oops in xe_gem_fault when running core_hotunplug test
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
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Version: unspecifiedKeywords: Security
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OS: Linux   
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A NULL pointer dereference flaw was found in the Linux kernel's Intel Xe GPU driver. In xe_gem_fault(), after a device hotplug unbind-rebind cycle, a race condition can occur where a process has memory mapped but the TTM buffer object's resource pointer becomes NULL. When the fault handler attempts to check the memory type via mem_type_is_vram(tbo->resource->mem_type), it dereferences the NULL pointer, causing a kernel panic. A local user could potentially trigger this through GPU hotplug operations.
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Description OSIDB Bzimport 2025-12-09 05:02:27 UTC 
In the Linux kernel, the following vulnerability has been resolved:

drm/xe: Fix oops in xe_gem_fault when running core_hotunplug test.

I saw an oops in xe_gem_fault when running the xe-fast-feedback
testlist against the realtime kernel without debug options enabled.

The panic happens after core_hotunplug unbind-rebind finishes.
Presumably what happens is that a process mmaps, unlocks because
of the FAULT_FLAG_RETRY_NOWAIT logic, has no process memory left,
causing ttm_bo_vm_dummy_page() to return VM_FAULT_NOPAGE, since
there was nothing left to populate, and then oopses in
"mem_type_is_vram(tbo->resource->mem_type)" because tbo->resource
is NULL.

It's convoluted, but fits the data and explains the oops after
the test exits.
Comment 1 Alexander B 2025-12-09 12:41:06 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2025120912-CVE-2025-40340-4d41@gregkh/T