Description

In the Linux kernel, the following vulnerability has been resolved: drm/vc4: Supply the overflow slot size in BPOS, not the whole bin BO size vc4_overflow_mem_work() points BPOA at a 512KB slot inside the 16MB binner BO, but writes the size of the whole BO to BPOS. On every binner out-of-memory event the PTB is therefore authorized to write tile lists across all the other slots (which may hold the tile state, tile alloc and overflow memory of in-flight jobs) and, for any slot but the first, past the end of the binner BO into unrelated CMA memory. Since CMA pages are recycled into page cache and user allocations, this is arbitrary memory corruption by GPU DMA. In practice it shows up as GPU hangs with corrupted control list pointers, userspace heap corruption, a GPU that stays permanently wedged after the first hang, and occasional full system crashes, whenever a job overflows the initial binner slot. The bug dates back to the conversion from a dedicated overflow BO (where writing the full BO size was correct) to the slotted binner BO.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "7.8",
  "pubDate": "2026-08-15T13:17:50.003Z",
  "pubdate": "2026-08-15T13:17:50.003Z",
  "executiveSummary": "An out-of-bounds memory corruption vulnerability exists in the Linux kernel's DRM VC4 driver, specifically within the binner buffer management handled by vc4_overflow_mem_work().\nThe vulnerability arises when the driver incorrectly supplies the total buffer object size instead of the specific overflow slot size to the BPOS register during a binner out-of-memory event.\nThis flaw allows the Primitive Thread Block (PTB) GPU DMA to write tile lists across unrelated memory regions, including other in-flight jobs' state allocations and arbitrary Contiguous Memory Allocator (CMA) pages.\nImpact includes arbitrary memory corruption via GPU DMA, leading to GPU hangs, userspace heap corruption, permanent device wedging, and full system crashes.\nThe issue affects systems utilizing the Broadcom VC4 GPU driver in the Linux kernel where slotted binner buffer objects are implemented, stemming from a historical regression during the conversion from dedicated overflow buffer objects.\nNo specific authentication or network exposure is required, as the vulnerability is triggered locally through GPU job submission and handling of binner memory overflows.",
  "technicalDetails": "The vulnerability resides in the Linux kernel's DRM subsystem within the Broadcom VC4 graphics driver, specifically in the function vc4_overflow_mem_work().\nRoot Cause: The driver points BPOA (Binner Packet Overflow Address) to a 512KB overflow slot inside a larger 16MB binner buffer object (BO), but mistakenly writes the size of the entire 16MB BO to BPOS (Binner Packet Overflow Size) instead of restricting it to the designated 512KB slot size.\nVulnerable Component: The VC4 DRM driver binner overflow memory management mechanism, specifically handling binner out-of-memory events.\nAttack Flow and Exploitation: When a rendering job triggers a binner out-of-memory event, the PTB is incorrectly authorized by the oversized BPOS value to write tile lists past the boundaries of the 512KB overflow slot. For the first slot, this permits writing over other active slots that hold tile state, tile alloc, and overflow memory of concurrent in-flight jobs. For subsequent slots, the writes extend past the end of the 16MB binner BO into unrelated CMA memory.\nPayload Behavior: Because CMA pages are dynamically recycled into the page cache and user space allocations, the GPU DMA writes result in arbitrary memory corruption across the system.\nPost-Exploitation Impact: In practical scenarios, this manifests as GPU hangs characterized by corrupted control list pointers, heap corruption within userspace applications, a permanently wedged GPU requiring a system reboot, and complete kernel crashes.\nPrerequisites: Exploitation or triggering of this vulnerability requires local execution privileges capable of submitting rendering jobs to the VC4 DRM driver that induce binner memory overflows."
}