CVE-2026-89814 in Linux
Summary
by MITRE • 09/16/2026
In the Linux kernel, the following vulnerability has been resolved:
drm/amdgpu: clamp the isolation index for rings outside a partition
adev->isolation[] has one slot per partition, but a ring that is not
assigned to one keeps AMDGPU_XCP_NO_PARTITION, which is ~0, so indexing the array with it is out of bounds. SDMA submissions hit this on both the isolation enforcement and the VM flush path and trip UBSAN.
Fall back to the first slot the way the cleaner shader path already does, and stop taking the address before the ring type check that makes it relevant.
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Analysis
by VulDB Data Team • 09/16/2026
The Linux kernel driver for AMD GPU hardware contains a critical out-of-bounds array access vulnerability within the amdgpu subsystem, specifically affecting the handling of graphics rings in systems utilizing XCP partitioning features. The root cause lies in how the driver manages isolation indices for ring buffers that are not assigned to a specific compute partition. In this architecture, each partition has a corresponding slot in the adev->isolation array, which is used to enforce hardware-level isolation between different virtualized contexts or partitions. However, when a ring buffer exists outside of any defined partition, it retains the value AMDGPU_XCP_NO_PARTITION for its isolation index. This constant resolves to approximately zero but with all bits set (bitwise NOT of zero), resulting in an extremely large unsigned integer value that far exceeds the valid bounds of the isolation array.
This technical flaw manifests during SDMA submission operations and virtual memory flush paths, where the driver attempts to access the isolation array using this invalid index. Because the index is effectively a massive positive number due to its representation as an unsigned type with all bits set, it triggers undefined behavior sanitizer checks within the kernel. The out-of-bounds read can lead to unpredictable system states, including potential information disclosure if sensitive memory adjacent to the array is accessed, or more commonly, immediate kernel panic and system instability. This issue highlights a failure in input validation where the driver assumes that all ring buffers will have valid partition assignments without adequately handling edge cases for unassigned resources.
From a security perspective, this vulnerability aligns with CWE-125, Out-of-bounds Read, as it involves accessing memory beyond the intended buffer boundary. It also relates to CWE-787, Out-of-bounds Write, if subsequent logic were to attempt writing based on such an index, although the primary reported impact is a read violation triggering UBSAN. In terms of attack vectors and defensive mapping, this flaw corresponds to MITRE ATT&CK technique T1059, Command and Scripting Interpreter, specifically in how kernel-level scripting or driver execution can be abused if memory corruption leads to code execution paths, though the immediate impact is stability rather than direct exploitation for privilege escalation. The vulnerability underscores the importance of robust boundary checks in low-level hardware drivers that interact directly with system resources.
The resolution involves modifying the amdgpu driver logic to clamp the isolation index when it falls outside valid partition ranges. Specifically, the code now defaults unassigned rings to use the first slot in the isolation array, mirroring the behavior already implemented for cleaner shader paths. This ensures that all ring buffers reference a valid memory location within the expected bounds of the isolation structure. Additionally, the fix removes an erroneous address calculation that occurred before the ring type check, further preventing potential invalid memory accesses. These changes restore stability and prevent undefined behavior during SDMA submissions and VM flushes.
To mitigate this vulnerability in environments running affected kernel versions, administrators should apply the latest available security patches for their Linux distribution immediately. Since this is a kernel-level driver issue affecting system stability, delaying patching increases the risk of unexpected crashes or denial-of-service conditions under heavy GPU load. Organizations relying on AMD hardware for compute-intensive tasks must ensure that their kernel updates include fixes from the amdgpu subsystem to maintain operational integrity and prevent potential exploitation vectors related to memory safety violations in privileged code paths.