Patch Tuesday CODE REVIEW: New Intel microcode and a new mitigation

Patch Tuesday CODE REVIEW: New Intel microcode and a new mitigation

[Dan McDonald]

Hello!

Intel has announced today both a microcode update for some CPUs, and the reason why they are updating it.

First, the microcode update:

	https://github.com/intel/Intel-Linux-Processor-Microcode-Data-Files/releases/tag/microcode-20240312

	https://code.illumos.org/c/illumos-gate/+/3371

This update enables detection of a vulnerability:  Register File Data Sampling (RFDS)

	https://www.intel.com/content/www/us/en/developer/articles/technical/software-security-guidance/advisory-guidance/register-file-data-sampling.html

The microcode update is NECESSARY, but NOT SUFFICIENT for mitigation.

The illumos mitigation (which re-enables an older VERW-use mitigation on the few Atom-class processors affected by RFDS) is here:

	https://code.illumos.org/c/illumos-gate/+/3372

I was HOPING to have this tested on afflicted hardware, but the machine I bought was so-Windows-locked I had to return it.

If anyone has "Alder Lake N" hardware (e.g Intel Processor N100) running illumos, PLEASE contact me ASAP so we can arrange before-and-after testing (there are some ways to detect the right thing happening using mdb).

These both are NOPs on non-modern-Atom-class hardware.

Thanks,
Dan