UBUNTU-CVE-2026-53139: Medium severity ubuntu/linux-hwe-edge vulnerability
In the Linux kernel, the following vulnerability has been resolved: drm/v3d: Skip CSD when it has zeroed workgroups A compute shader dispatch encodes its workgroup counts in the CFG0..CFG2 registers. Kicking off a dispatch with a zero count in any of the three dimensions is invalid. First, the hardware will process 0 as 65536, while the user-space driver exposes a maximum of 65535. Over that, a submission with a zeroed workgroup dimension should be a no-op. These zeroed counts can reach the dispatch path through an indirect CSD job, whose workgroup counts are only known once the indirect buffer is read and may legitimately be zero, but such scenario should only result in a no-op. Overwrite the indirect CSD job workgroup counts with the indirect BO ones, even if they are zeroed, and don't submit the job to the hardware when any of the workgroup counts is zero, so the job completes immediately instead of running the shader.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
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ubuntu/linux-riscvto a version that resolves this vulnerability.Fixed in 7.0.0-31.31.1 - Compensating control
For indirect CSD jobs, overwrite the workgroup counts with the indirect buffer object's counts, including zero values, and do not submit the job to hardware when any of the three workgroup counts is zero; complete the job immediately as a no-op.
Event History
Frequently Asked Questions
Who is realistically exposed to this issue?
Systems using an affected Ubuntu kernel package with the V3D graphics driver are relevant. Exploitation requires a local low-privileged user able to submit compute shader dispatches through the graphics stack.
What condition triggers the unintended shader execution?
A compute shader dispatch must have a zero workgroup count in at least one dimension. This can occur through an indirect CSD job after its workgroup counts are read from the indirect buffer; the hardware interprets a zero count as 65536 rather than treating it as a no-op.
How can I tell whether a workload may be affected?
Review GPU compute workloads using indirect CSD jobs for workgroup-count buffers that can contain zero in any dimension. Affected behavior is indicated when such a job is submitted to V3D hardware instead of completing immediately as a no-op.
What mitigation is available if an updated kernel cannot be deployed immediately?
Prevent untrusted local users or workloads from submitting V3D compute shader jobs, particularly indirect CSD dispatches. Ensure applications do not submit indirect workgroup counts with zero in any dimension.