CVE-2021-47018: powerpc/64: Fix the definition of the fixmap area

CVE-2021-47018: powerpc/64: Fix the definition of the fixmap area

[Greg Kroah-Hartman]

From: gregkh@kernel.org

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

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

powerpc/64: Fix the definition of the fixmap area

At the time being, the fixmap area is defined at the top of
the address space or just below KASAN.

This definition is not valid for PPC64.

For PPC64, use the top of the I/O space.

Because of circular dependencies, it is not possible to include
asm/fixmap.h in asm/book3s/64/pgtable.h , so define a fixed size
AREA at the top of the I/O space for fixmap and ensure during
build that the size is big enough.

The Linux kernel CVE team has assigned CVE-2021-47018 to this issue.


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

	Issue introduced in 5.5 with commit 265c3491c4bc and fixed in 5.10.37 with commit 4b9fb2c9039a
	Issue introduced in 5.5 with commit 265c3491c4bc and fixed in 5.11.21 with commit abb07dc5e8b6
	Issue introduced in 5.5 with commit 265c3491c4bc and fixed in 5.12.4 with commit a84df7c80bda
	Issue introduced in 5.5 with commit 265c3491c4bc and fixed in 5.13 with commit 9ccba66d4d2a

Please see https://www.kernel.org or 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-2021-47018
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/include/asm/book3s/64/pgtable.h
	arch/powerpc/include/asm/fixmap.h
	arch/powerpc/include/asm/nohash/64/pgtable.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/4b9fb2c9039a206d37f215936a4d5bee7b1bf9cd
	https://git.kernel.org/stable/c/abb07dc5e8b61ab7b1dde20dd73aa01a3aeb183f
	https://git.kernel.org/stable/c/a84df7c80bdac598d6ac9268ae578da6928883e8
	https://git.kernel.org/stable/c/9ccba66d4d2aff9a3909aa77d57ea8b7cc166f3c