Subject: CVE-2021-47567: powerpc/32: Fix hardlockup on vmap stack overflow

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

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

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

powerpc/32: Fix hardlockup on vmap stack overflow

Since the commit c118c7303ad5 ("powerpc/32: Fix vmap stack - Do not
activate MMU before reading task struct") a vmap stack overflow
results in a hard lockup. This is because emergency_ctx is still
addressed with its virtual address allthough data MMU is not active
anymore at that time.

Fix it by using a physical address instead.

The Linux kernel CVE team has assigned CVE-2021-47567 to this issue.

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

	Issue introduced in 5.10 with commit c118c7303ad5 and fixed in 5.10.83 with commit dfe906da9a1a
	Issue introduced in 5.10 with commit c118c7303ad5 and fixed in 5.15.6 with commit c4e3ff8b8b1d
	Issue introduced in 5.10 with commit c118c7303ad5 and fixed in 5.16 with commit 5bb60ea611db
	Issue introduced in 5.9.5 with commit 3b234b4a6651

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-2021-47567
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:
	arch/powerpc/kernel/head_32.h

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/dfe906da9a1abebdebe8b15bb3e66a2578f6c4c7
	https://git.kernel.org/stable/c/c4e3ff8b8b1d54f0c755670174c453b06e17114b
	https://git.kernel.org/stable/c/5bb60ea611db1e04814426ed4bd1c95d1487678e