CVE-2020-36787: Undefined Security Weakness

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

media: aspeed: fix clock handling logic

Video engine uses eclk and vclk for its clock sources and its reset control is coupled with eclk so the current clock enabling sequence works like below.

Enable eclk De-assert Video Engine reset 10ms delay Enable vclk

It introduces improper reset on the Video Engine hardware and eventually the hardware generates unexpected DMA memory transfers that can corrupt memory region in random and sporadic patterns. This issue is observed very rarely on some specific AST2500 SoCs but it causes a critical kernel panic with making a various shape of signature so it's extremely hard to debug. Moreover, the issue is observed even when the video engine is not actively used because udevd turns on the video engine hardware for a short time to make a query in every boot.

To fix this issue, this commit changes the clock handling logic to make the reset de-assertion triggered after enabling both eclk and vclk. Also, it adds clk_unprepare call for a case when probe fails.

clk: ast2600: fix reset settings for eclk and vclk Video engine reset setting should be coupled with eclk to match it with the setting for previous Aspeed SoCs which is defined in clk-aspeed.c since all Aspeed SoCs are sharing a single video engine driver. Also, reset bit 6 is defined as 'Video Engine' reset in datasheet so it should be de-asserted when eclk is enabled. This commit fixes the setting.