CVE-2024-35942

What it actually does

Missing fdcc clock enable in the hdmimix power domain allows the clock to remain disabled before HDMI/LCDIF probe, preventing LCDIF from obtaining the pixel clock from the HDMI PHY and triggering vblank timeouts plus drm_atomic_helper warnings.

Why it matters to the business

Display initialization failures on affected embedded systems can disrupt multimedia, signage, or industrial interfaces until the kernel is updated, increasing downtime on i.MX8MP hardware.

How an attack unfolds

An attacker or misconfigured environment disables the fdcc clock prior to driver probe sequences; the missing clock then blocks pixel clock delivery during HDMI TX or LCDIF initialization, producing kernel warnings and potential denial of service in the display stack.

How to fix it

Update the Linux kernel to the fixed commit 9d3f959b426635c4da50dfc7b1306afd84d23e7c or later; ensure fdcc clock is added to both LCDIF and HDMI TX power domains in imx8mp-blk-ctrl.

How to confirm the fix worked

After patching, confirm fdcc clock is referenced in hdmimix domain power-domain definitions and verify absence of 'vblank wait timed out' messages during HDMI/LCDIF initialization on i.MX8MP hardware.

Typical attack path

1. Boot or reset system with fdcc clock disabled for hdmimix domain
2. Allow HDMI and LCDIF drivers to probe before clock is enabled
3. Trigger vblank wait operations that time out due to absent pixel clock
4. Observe kernel warnings and potential display subsystem failure

How to detect it

Search kernel logs for 'vblank wait timed out' together with WARNING entries referencing drivers/gpu/drm/drm_atomic_helper.c during early boot or HDMI probe; correlate with imx8mp-blk-ctrl clock configuration changes.

• vblank wait timed out
• drm_atomic_helper_wait_for_vblanks.part.0
• WARNING: CPU:.* at drivers/gpu/drm/drm_atomic_helper.c:1634

What your security team should do

• Prioritize kernel update on all i.MX8MP-based devices within maintenance windows
• Add kernel log monitoring for drm_atomic_helper vblank warnings as a temporary detection control
• Test display functionality post-update on representative hardware configurations