(RHSA-2018:0496) Important: kernel security and bug fix update

The kernel packages contain the Linux kernel, the core of any Linux operating system.

Security Fix(es):

• hw: cpu: speculative execution branch target injection (s390-only) (CVE-2017-5715, Important)

• hw: cpu: speculative execution bounds-check bypass (s390 and powerpc) (CVE-2017-5753, Important)

• hw: cpu: speculative execution permission faults handling (powerpc-only) (CVE-2017-5754)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

Bug Fix(es):

• If an NFSv3 client mounted a subdirectory of an exported file system, a directory entry to the mount hosting the export was incorrectly held even after clearing the cache. Consequently, attempts to unmount the subdirectory with the umount command failed with the EBUSY error. With this update, the underlying source code has been fixed, and the unmount operation now succeeds as expected in the described situation. (BZ#1538587)

• The Return Trampoline (Retpoline) mechanism mitigates the branch target injection, also known as the Spectre variant 2 vulnerability. With this update, Retpoline has been implemented into the Red Hat Enterprise Linux kernel. (BZ#1543023)