[PATCH 0/1][SRU][B] CVE-2018-18281 - stale TLB entries via mremap()

[Tyler Hicks]

https://people.canonical.com/~ubuntu-security/cve/2018/CVE-2018-18281.html

 Since Linux kernel version 3.2, the mremap() syscall performs TLB flushes
 after dropping pagetable locks. If a syscall such as ftruncate() removes
 entries from the pagetables of a task that is in the middle of mremap(), a
 stale TLB entry can remain for a short time that permits access to a
 physical page after it has been released back to the page allocator and
 reused. This is fixed in the following kernel versions: 4.9.135, 4.14.78,
 4.18.16, 4.19.

Clean cherry pick to Bionic. I tested this change using the --mremap
stressor of stress-ng.

Tyler