CVE-2022-48991

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.