A flaw was found in the patches used to fix the 'dirtycow' vulnerability (CVE-2016-5195). An attacker, able to run local code, can exploit a race condition in transparent huge pages to modify usually read-only huge pages.
Find out more about CVE-2017-1000405 from the
MITRE CVE dictionary dictionary and
From the initial flaw description released, this issue does not affect the Linux kernel packages as shipped with Red Hat Enterprise Linux 5, 6, 7 and Red Hat Enterprise MRG 2. They do not contain the upstream commit (8310d48b125d19fcd9521d83b8293e63eb1646aa) which allows the race condition.
This issue affects the Linux kernel packages as shipped with Red Hat Enterprise Linux 7 for ARM and Red Hat Enterprise Linux for Power LE kernel-alt packages.
Future Linux kernel updates for the respective releases may address this issue.
For further information please refer to the vulnerability article in the Customer Portal: https://access.redhat.com/security/vulnerabilities/3253921
Disabling the use of zero page:
It is possible to prevent the zero page from being mapped as a huge page, by modifying a configuration tunable in the /sys directory as shown below. This prevents the flaw from being exercised in this method.
# echo 0 > /sys/kernel/mm/transparent_hugepage/use_zero_page
Disabling huge pages:
It is possible to mitigate this flaw by disabling hugepages on a system. Some user applications may require hugepages to be performant, and may suffer a performance penalty when running without hugepages.
Red Hat has existing solutions created instructing how to disable transparent
How to disable transparent hugepages (THP) on Red Hat Enterprise Linux 7
If your application may require transparent huge pages, please consult your software vendor to confirm.