USN-3541-2: Linux kernel (HWE) vulnerabilities

USN-3541-1 addressed vulnerabilities in the Linux kernel for Ubuntu 17.10. This update provides the corresponding updates for the Linux Hardware Enablement (HWE) kernel from Ubuntu 17.10 for Ubuntu 16.04 LTS. Jann Horn discovered that microprocessors utilizing speculative execution and branch prediction may allow unauthorized memory reads via sidechannel attacks. This flaw is known as Spectre. A local attacker could use this to expose sensitive information, including kernel memory. This update provides mitigations for the i386 (CVE-2017-5753 only), amd64, ppc64el, and s390x architectures. (CVE-2017-5715, CVE-2017-5753) USN-3523-2 mitigated CVE-2017-5754 (Meltdown) for the amd64 architecture in the Linux Hardware Enablement (HWE) kernel from Ubuntu 17.10 for Ubuntu 16.04 LTS. This update provides the corresponding mitigations for the ppc64el architecture. 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. (CVE-2017-5754)