(RHSA-2018:2161) Important: kernel security and bug fix 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, x86 AMD)

Red Hat would like to thank Ken Johnson (Microsoft Security Response Center) and Jann Horn (Google Project Zero) for reporting this issue.

Bug Fix(es):

• When a Nonvolatile Memory Express (NVMe) namespace was created, changed, or deleted, an occasional deadlock occurred. With this update, namespace scanning and removal does not hold a mutual exclusion (mutex) program object. As a result, a deadlock no longer occurs in the described scenario. (BZ#1566886)

• Previously, a live migration of a virtual machine from one host with updated firmware to another host without updated firmware resulted in incorrect kernel settings for Meltdown mitigations, which could leave the kernel vulnerable to Meltdown. With this fix, the firmware on the new physical host is re-scanned for updates after a live migration. As a result, the kernel uses the correct mitigation in the described scenario. (BZ#1570507)

• Previously, microcode updates on 32 and 64-bit AMD and Intel architectures were not synchronized. As a consequence, it was not possible to apply the microcode updates. This fix adds the synchronization to the microcode updates so that processors of the stated architectures receive updates at the same time. As a result, microcode updates are now synchronized. (BZ#1578044)

• When switching from the indirect branch speculation (IBRS) feature to the retpolines feature, the IBRS state of some CPUs was sometimes not handled correctly. Consequently, some CPUs were left with the IBRS Model-Specific Register (MSR) bit set to 1, which could lead to performance issues. With this update, the underlying source code has been fixed to clear the IBRS MSR bits correctly, thus fixing the bug. (BZ#1586146)

Users of kernel are advised to upgrade to these updated packages, which fix these bugs.

The system must be rebooted for this update to take effect.