USN-3522-2 fixed a vulnerability in the Linux Hardware Enablement kernel for Ubuntu 14.04 LTS to address Meltdown (CVE-2017-5754). Unfortunately, that update introduced a regression where a few systems failed to boot successfully. This update fixes the problem.
We apologize for the inconvenience.
Original advisory details:
Jann Horn discovered that microprocessors utilizing speculative execution and indirect branch prediction may allow unauthorized memory reads via sidechannel attacks. This flaw is known as Meltdown. A local attacker could use this to expose sensitive information, including kernel memory.