RHSA-2018:1639: Important: kernel security update

The kernel packages contain the Linux kernel, the core of any Linux operating system.Security Fix(es): An industry-wide issue was found in the way many modern microprocessor designs have implemented speculative execution of Load & Store instructions (a commonly used performance optimization). It relies on the presence of a precisely-defined instruction sequence in the privileged code as well as the fact that memory read from address to which a recent memory write has occurred may see an older value and subsequently cause an update into the microprocessor's data cache even for speculatively executed instructions that never actually commit (retire). As a result, an unprivileged attacker could use this flaw to read privileged memory by conducting targeted cache side-channel attacks. (CVE-2018-3639) Note: This issue is present in hardware and cannot be fully fixed via software update. The updated kernel packages provide software side of the mitigation for this hardware issue. To be fully functional, up-to-date CPU microcode applied on the system is required. Please refer to References section for further information about this issue, CPU microcode requirements and the potential performance impact.Red Hat would like to thank Ken Johnson (Microsoft Security Response Center) and Jann Horn (Google Project Zero) for reporting this issue.