Subject: CVE-2022-48991: mm/khugepaged: invoke MMU notifiers in shmem/file collapse paths

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

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

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

mm/khugepaged: invoke MMU notifiers in shmem/file collapse paths

Any codepath that zaps page table entries must invoke MMU notifiers to
ensure that secondary MMUs (like KVM) don't keep accessing pages which
aren't mapped anymore.  Secondary MMUs don't hold their own references to
pages that are mirrored over, so failing to notify them can lead to page
use-after-free.

I'm marking this as addressing an issue introduced in commit f3f0e1d2150b
("khugepaged: add support of collapse for tmpfs/shmem pages"), but most of
the security impact of this only came in commit 27e1f8273113 ("khugepaged:
enable collapse pmd for pte-mapped THP"), which actually omitted flushes
for the removal of present PTEs, not just for the removal of empty page
tables.

The Linux kernel CVE team has assigned CVE-2022-48991 to this issue.

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

	Issue introduced in 4.8 with commit f3f0e1d2150b and fixed in 4.9.337 with commit 275c626c131c
	Issue introduced in 4.8 with commit f3f0e1d2150b and fixed in 4.14.303 with commit c23105673228
	Issue introduced in 4.8 with commit f3f0e1d2150b and fixed in 4.19.270 with commit ff2a1a6f8696
	Issue introduced in 4.8 with commit f3f0e1d2150b and fixed in 5.4.227 with commit 5ffc2a75534d
	Issue introduced in 4.8 with commit f3f0e1d2150b and fixed in 5.10.159 with commit 7f445ca2e0e5
	Issue introduced in 4.8 with commit f3f0e1d2150b and fixed in 5.15.83 with commit 1a3f8c6cd29d
	Issue introduced in 4.8 with commit f3f0e1d2150b and fixed in 6.0.13 with commit 5450535901d8
	Issue introduced in 4.8 with commit f3f0e1d2150b and fixed in 6.1 with commit f268f6cf875f

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-2022-48991
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:
	mm/khugepaged.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/275c626c131cfe141beeb6c575e31fa53d32da19
	https://git.kernel.org/stable/c/c23105673228c349739e958fa33955ed8faddcaf
	https://git.kernel.org/stable/c/ff2a1a6f869650aec99e9d070b5ab625bfbc5bc3
	https://git.kernel.org/stable/c/5ffc2a75534d9d74d49760f983f8eb675fa63d69
	https://git.kernel.org/stable/c/7f445ca2e0e59c7971d0b7b853465e50844ab596
	https://git.kernel.org/stable/c/1a3f8c6cd29d9078cc81b29d39d0e9ae1d6a03c3
	https://git.kernel.org/stable/c/5450535901d89a5dcca5fbbc59a24fe89caeb465
	https://git.kernel.org/stable/c/f268f6cf875f3220afc77bdd0bf1bb136eb54db9