(RHSA-2018:2006) Important: libvirt security and bug fix update

The libvirt library contains a C API for managing and interacting with the virtualization capabilities of Linux and other operating systems. In addition, libvirt provides tools for remote management of virtualized systems.

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 is the libvirt side of the CVE-2018-3639 mitigation that includes support for guests running on hosts with AMD CPUs.

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):

• The “virsh capabilities” command previously displayed an inaccurate number of 4 KiB memory pages on systems with very large amounts of memory. This update optimizes the memory diagnostic mechanism to ensure memory page numbers are displayed correctly on such systems. (BZ#1582416)

• After starting a large amount of guest virtual machines in a single session, the libvirtd service in some cases became unable to start any other guests until it was restarted. This update ensures that libvirtd properly frees memory used for D-Bus replies, which prevents the described problem from occurring. (BZ#1588390)