Subject: CVE-2020-36787: media: aspeed: fix clock handling logic

From: Greg Kroah-Hartman <[email-masked]>

Description
===========

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.

The Linux kernel CVE team has assigned CVE-2020-36787 to this issue.

Affected and fixed versions
===========================

	Issue introduced in 5.0 with commit d2b4387f3bdf and fixed in 5.4.119 with commit 1dc1d30ac101
	Issue introduced in 5.0 with commit d2b4387f3bdf and fixed in 5.10.37 with commit a59d01384c80
	Issue introduced in 5.0 with commit d2b4387f3bdf and fixed in 5.11.21 with commit 2964c37563e8
	Issue introduced in 5.0 with commit d2b4387f3bdf and fixed in 5.12.4 with commit 75321dc8aebe
	Issue introduced in 5.0 with commit d2b4387f3bdf and fixed in 5.13 with commit 3536169f8531

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2020-36787
will be updated if fixes are backported, please check that for the most
up to date information about this issue.

Affected files
==============

The file(s) affected by this issue are:
	drivers/clk/clk-ast2600.c
	drivers/media/platform/aspeed-video.c

Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/1dc1d30ac101bb8335d9852de2107af60c2580e7
	https://git.kernel.org/stable/c/a59d01384c80a8a4392665802df57c3df20055f5
	https://git.kernel.org/stable/c/2964c37563e86cfdc439f217eb3c5a69adfdba6a
	https://git.kernel.org/stable/c/75321dc8aebe3f30eff226028fe6da340fe0bf02
	https://git.kernel.org/stable/c/3536169f8531c2c5b153921dc7d1ac9fd570cda7