Linux 4.19 Will Have Enhanced IBRS For Better Spectre V2 Protection On Future Intel CPUs

Besides the Linux 4.19 kernel slated to introduce initial SpectreRSB protection, this next kernel version should also introduce support for Enhanced IBRS as a better means of Spectre Variant Two mitigation to be supported by future Intel CPUs.

Last month I wrote about an Intel engineer preparing a Linux kernel patch to handle enhanced IBRS. IBRS as a reminder is the Indirect Branch Restricted Speculation. The enhanced IBRS mode aims to let up on the performance impact of Spectre V2 mitigation compared to current x86 CPUs.

On the yet-to-be-relased Intel CPUs supporting enhanced IBRS, with the kernel patch it will be used rather than the existing Retpolines (return trampolines) approach.

The enhanced IBRS patch is now queued into Thomas Gleixner's x86/pti Git tree -- along with the SpectreRSB patch -- of the new material that should be merged for the upcoming Linux 4.19 kernel cycle.