Retpoline Backported To Linux 4.9, Linux 4.14 Kernels
Written by Michael Larabel in Linux Kernel on 15 January 2018 at 08:38 AM EST. 16 Comments
LINUX KERNEL --
Retpoline support for mitigating the Spectre vulnerabilities will soon be present in the Linux 4.9 and 4.14 stable kernels.

Greg Kroah-Hartman has sent out the latest patches for the Linux 4.9 and 4.14 point releases, which now include the Retpoline support.

This X86_FEATURE_RETPOLINE is enabled for all AMD/Intel CPUs. For full support you also need to be building the kernel with a newer GCC compiler containing -mindirect-branch=thunk-extern support. The GCC changes landed in GCC 8.0 yesterday and is in the process of potentially being back-ported to GCC 7.3.

Those wanting to disable the Retpoline support can boot the patched kernels with noretpoline.

This Retpoline support will be found in the soon-to-be-released Linux 4.9.77 and 4.14.14 kernels.

Greg did send out new patches today for the Linux 4.4 and 3.18 stable series today, but they do not contain Retpoline support. But at least does include the sysfs additions for noting if the CPU is vulnerable to Spectre.

Linux 4.15 has Retpoline support as of a few days ago.

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Michael Larabel is the principal author of Phoronix.com and founded the site in 2004 with a focus on enriching the Linux hardware experience. Michael has written more than 10,000 articles covering the state of Linux hardware support, Linux performance, graphics drivers, and other topics. Michael is also the lead developer of the Phoronix Test Suite, Phoromatic, and OpenBenchmarking.org automated benchmarking software. He can be followed via Twitter or contacted via MichaelLarabel.com.

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