The kernel packages contain the Linux kernel, the core of any Linux operating system.
An industry-wide issue was found in the way many modern microprocessor designs have implemented speculative execution of instructions (a commonly used performance optimization). There are three primary variants of the issue which differ in the way the speculative execution can be exploited. Variant CVE-2017-5754 relies on the fact that, on impacted microprocessors, during speculative execution of instruction permission faults, exception generation triggered by a faulting access is suppressed until the retirement of the whole instruction block. In a combination with the fact that memory accesses may populate the cache even when the block is being dropped and never committed (executed), an unprivileged local attacker could use this flaw to read privileged (kernel space) memory by conducting targeted cache side-channel attacks. (CVE-2017-5754, Important, KVM for Power)
Red Hat would like to thank Google Project Zero for reporting this issue.
These updated kernel packages include also numerous bug fixes. Space precludes documenting all of these bug fixes in this advisory. See the bug fix descriptions in the related Knowledge Article: https://access.redhat.com/articles/3413511