CVE-2026-68437 Overview
CVE-2026-68437 is a Linux kernel vulnerability in the drm/imagination (PowerVR) GPU driver. The flaw affects how the DRM scheduler handles paired geometry and fragment jobs when checking Circular Command Control Buffer (CCCB) space. The pvr_queue_prepare_job() function fails to account for the mismatched fragment job and geometry queue, causing space checks to be performed against the wrong CCCB.
When the scheduler wrongly assumes sufficient space exists, run_job() returns early without writing the full command sequence. This produces kernel warnings in pvr_cccb_write_command_with_header and can lead to job timeouts depending on waiters for the missing commands.
Critical Impact
Local GPU workloads on affected PowerVR hardware can trigger kernel warnings and job timeouts, resulting in denial of service conditions on the graphics subsystem.
Affected Products
- Linux kernel with the drm/imagination (PowerVR) driver enabled
- Systems using Imagination Technologies PowerVR GPUs (for example, Texas Instruments AM625 SK platforms)
- Kernel builds prior to the fixes referenced in commits 15a9863, 4baf9e7, 4ddf82c, and e2c29d5
Discovery Timeline
- 2026-08-12 - CVE-2026-68437 published to NVD
- 2026-08-12 - Last updated in NVD database
Technical Details for CVE-2026-68437
Vulnerability Analysis
The vulnerability resides in the PowerVR DRM driver's job submission path. For geometry jobs paired with a fragment job, the DRM scheduler's prepare_job() callback executes a three-step process. It checks internal driver dependencies for the geometry job, calls pvr_queue_get_paired_frag_job_dep() for the fragment job's external dependencies, and then invokes prepare_job() again for the fragment job's internal dependencies.
The nested invocation passes the fragment job's drm_sched_job together with the geometry job's drm_sched_entity and pvr_queue. This queue mismatch causes pvr_queue_prepare_job() to check available CCCB space against the geometry queue rather than the fragment queue.
When the geometry CCCB has space but the fragment CCCB does not, run_job() proceeds and returns early without writing the complete command sequence. The resulting incomplete state produces kernel warnings from pvr_cccb_write_command_with_header+0x2c4/0x330 and may block downstream waiters, causing GPU job timeouts.
Root Cause
The root cause is an incorrect queue context during the nested prepare_job() callback for paired fragment jobs. The function inspects the wrong CCCB when validating space availability, an instance of state confusion between two related but distinct submission queues.
Attack Vector
The vulnerability is triggered by legitimate GPU workloads submitting paired geometry and fragment jobs through the DRM interface. No privileged access beyond normal GPU device access is required, but exploitation is limited to denial of service on the graphics subsystem. There is no verified path to code execution or privilege escalation.
The fix moves the initialisation of the paired fragment job's done fence and CCCB fence into pvr_queue_get_paired_frag_job_dep(), where the correct queue is inferred directly from the fragment job. See the kernel patch commit e2c29d5 for the full remediation.
Detection Methods for CVE-2026-68437
Indicators of Compromise
- Kernel warnings referencing pvr_cccb_write_command_with_header+0x2c4/0x330 [powervr] in dmesg or system logs
- Call traces including pvr_queue_submit_job_to_cccb and pvr_queue_run_job from the powervr-sched workqueue
- GPU job timeouts on systems using Imagination PowerVR hardware
Detection Strategies
- Monitor kernel logs for WARNING entries originating from drivers/gpu/drm/imagination/pvr_cccb.c:178
- Track kernel taint flags transitioning to W (warning) state on PowerVR-equipped devices
- Correlate GPU workload failures with matching timestamps in kernel warning traces
Monitoring Recommendations
- Ingest dmesg and journalctl -k output into a centralized log platform for warning-level analysis
- Alert on repeated powervr module warnings, which may indicate a triggering workload pattern
- Track kernel version inventory to identify systems still running vulnerable builds
How to Mitigate CVE-2026-68437
Immediate Actions Required
- Identify Linux systems running the powervr DRM driver and enumerate their kernel versions
- Apply the upstream stable kernel updates containing the four referenced fix commits
- Reboot affected systems after patching to ensure the corrected driver is loaded
Patch Information
The fix is available in the mainline and stable kernel trees through the following commits: Kernel Git Commit 15a9863, Kernel Git Commit 4baf9e7, Kernel Git Commit 4ddf82c, and Kernel Git Commit e2c29d5. Distribution vendors should backport these commits into their supported stable branches.
Workarounds
- Where GPU acceleration is not required, unload the powervr module to avoid triggering the code path
- Restrict local user access to the DRM device nodes to reduce exposure to untrusted workloads
- Where feasible, avoid workloads that submit paired geometry and fragment jobs until the patched kernel is deployed
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
