CVE-2024-56683

What it actually does

Reading HDMI debug registers from sysfs while the HDMI controller is suspended disables the DVP clock, leaving AXI bus accesses to hang the system.

Why it matters to the business

Local users or automated scripts can trigger an immediate, unrecoverable system freeze on affected Linux kernels, causing denial of service and potential data loss for unsaved work.

How an attack unfolds

An attacker with local access reads /sys/kernel/debug/dri/*/hdmi*_regs while the HDMI output is disconnected and the kernel has suspended the display clocks, causing the AXI transaction to hang indefinitely.

How to fix it

Update the Linux kernel to a version containing commit 3d7cb6b04c3f3115719235cc6866b10326de34cd or later; apply the vendor-supplied package that includes this fix.

How to confirm the fix worked

Verify the running kernel Git commit or package version contains 3d7cb6b04c3f3115719235cc6866b10326de34cd; attempt the debug-register read while suspended and confirm the system no longer hangs.

Typical attack path

1. Obtain local shell or script execution on the target system
2. Ensure or wait for HDMI to be disconnected and the device suspended
3. Read the vc4 HDMI debug register file under /sys/kernel/debug/dri/
4. Trigger fatal AXI hang that freezes the kernel

How to detect it

Review system and kernel logs for sudden AXI or DRM-related hangs coinciding with reads of vc4 HDMI debug files; look for processes accessing /sys/kernel/debug/dri/*/hdmi*_regs while the display is suspended.

What your security team should do

• Prioritize kernel updates on all systems exposing vc4 HDMI debugfs
• Restrict local access to /sys/kernel/debug/dri/ until patched
• Monitor for kernel updates in the distribution security feed