CVE-2024-40916: drm/exynos: hdmi: report safe 640x480 mode as a fallback when no EDID found

In the Linux kernel, the following vulnerability has been resolved:

drm/exynos: hdmi: report safe 640x480 mode as a fallback when no EDID found

When reading EDID fails and driver reports no modes available, the DRM core adds an artificial 1024x786 mode to the connector. Unfortunately some variants of the Exynos HDMI (like the one in Exynos4 SoCs) are not able to drive such mode, so report a safe 640x480 mode instead of nothing in case of the EDID reading failure.

This fixes the following issue observed on Trats2 board since commit 13d5b040363c ("drm/exynos: do not return negative values from .getmodes()"):

[drm] Exynos DRM: using 11c00000.fimd device for DMA mapping operations exynos-drm exynos-drm: bound 11c00000.fimd (ops fimdcomponentops) exynos-drm exynos-drm: bound 12c10000.mixer (ops mixercomponentops) exynos-dsi 11c80000.dsi: [drm:samsungdsimhostattach] Attached s6e8aa0 device (lanes:4 bpp:24 mode-flags:0x10b) exynos-drm exynos-drm: bound 11c80000.dsi (ops exynosdsicomponentops) exynos-drm exynos-drm: bound 12d00000.hdmi (ops hdmicomponentops) [drm] Initialized exynos 1.1.0 20180330 for exynos-drm on minor 1 exynos-hdmi 12d00000.hdmi: [drm:hdmiphyenable.part.0] ERROR PLL could not reach steady state panel-samsung-s6e8aa0 11c80000.dsi.0: ID: 0xa2, 0x20, 0x8c exynos-mixer 12c10000.mixer: timeout waiting for VSYNC ------------[ cut here ]------------ WARNING: CPU: 1 PID: 11 at drivers/gpu/drm/drmatomichelper.c:1682 drmatomichelperwaitforvblanks.part.0+0x2b0/0x2b8 [CRTC:70:crtc-1] vblank wait timed out Modules linked in: CPU: 1 PID: 11 Comm: kworker/u16:0 Not tainted 6.9.0-rc5-next-20240424 #14913 Hardware name: Samsung Exynos (Flattened Device Tree) Workqueue: eventsunbound deferredprobeworkfunc Call trace: unwindbacktrace from showstack+0x10/0x14 showstack from dumpstacklvl+0x68/0x88 dumpstacklvl from warn+0x7c/0x1c4 warn from warnslowpathfmt+0x11c/0x1a8 warnslowpathfmt from drmatomichelperwaitforvblanks.part.0+0x2b0/0x2b8 drmatomichelperwaitforvblanks.part.0 from drmatomichelpercommittailrpm+0x7c/0x8c drmatomichelpercommittailrpm from committail+0x9c/0x184 committail from drmatomichelpercommit+0x168/0x190 drmatomichelpercommit from drmatomiccommit+0xb4/0xe0 drmatomiccommit from drmclientmodesetcommitatomic+0x23c/0x27c drmclientmodesetcommitatomic from drmclientmodesetcommitlocked+0x60/0x1cc drmclientmodesetcommitlocked from drmclientmodesetcommit+0x24/0x40 drmclientmodesetcommit from drmfbhelperrestorefbdevmodeunlocked+0x9c/0xc4 drmfbhelperrestorefbdevmodeunlocked from drmfbhelpersetpar+0x2c/0x3c drmfbhelpersetpar from fbconinit+0x3d8/0x550 fbconinit from visualinit+0xc0/0x108 visualinit from dobindcondriver+0x1b8/0x3a4 dobindcondriver from dotakeoverconsole+0x140/0x1ec dotakeoverconsole from dofbcontakeover+0x70/0xd0 dofbcontakeover from fbconfbregistered+0x19c/0x1ac fbconfbregistered from registerframebuffer+0x190/0x21c registerframebuffer from drmfbhelperinitialconfigandunlock+0x350/0x574 drmfbhelperinitialconfigandunlock from exynosdrmfbdevclienthotplug+0x6c/0xb0 exynosdrmfbdevclienthotplug from drmclientregister+0x58/0x94 drmclientregister from exynosdrmbind+0x160/0x190 exynosdrmbind from trytobringupaggregatedevice+0x200/0x2d8 trytobringupaggregatedevice from componentadd+0xb0/0x170 componentadd from mixerprobe+0x74/0xcc mixerprobe from platformprobe+0x5c/0xb8 platformprobe from reallyprobe+0xe0/0x3d8 reallyprobe from driverprobedevice+0x9c/0x1e4 driverprobedevice from driverprobedevice+0x30/0xc0 driverprobedevice from deviceattachdriver+0xa8/0x120 deviceattachdriver from busforeachdrv+0x80/0xcc busforeachdrv from deviceattach+0xac/0x1fc deviceattach from busprobedevice+0x8c/0x90 busprobedevice from deferredprobeworkfunc+0 ---truncated---