Own an Skylake or Kaby Lake processor with Hyper-Threading? It may be a good time to update your system UEFI/BIOS and CPU microcode. A critical flaw in Intel’s implementation of Hyper-Threading was recently revealed by the Debian Linux mailing list.

The critical flaw, which exists on all Intel 6th Generation “Skylake” and 7th Generation “Kaby Lake” processors with Hyper-Threading may cause “unpredictable system behavior” under a specific set of circumstances.

According to the Intel’s official documentation:

Errata: SKZ7/SKW144/SKL150/SKX150/SKZ7/KBL095/KBW095
Short Loops Which Use AH/BH/CH/DH Registers May Cause
Unpredictable System Behavior.

Problem: Under complex micro-architectural conditions, short loops
of less than 64 instructions that use AH, BH, CH or DH
registers as well as their corresponding wider register
(e.g. RAX, EAX or AX for AH) may cause unpredictable
system behavior. This can only happen when both logical
processors on the same physical processor are active.

Implication: Due to this erratum, the system may experience
unpredictable system behavior.

Technology publication HotHardware recently reached out to Intel, which told the site that the issue has been identified and addressed as of April 2017; however, it’s up to the end user to run the appropriate BIOS/UEFI updates with the updated microcode.


Source: Debian Mailing List via HotHardware