A critical flaw has been discovered in Intel Corp.’s Skylake and Kaby Lake chips that could result in application and data issues, according to a newly published report.

The issue is said to be the result of a microcode bug in Intel’s hyperthreading process and affects Skylake and Kaby Lake Intel Core central processing unit chips for desktop, embedded and mobile devices, Xeon v5 and v6 server processors and some Pentium models. Reported by Linux operating system maker Debian but applicable to any operating system using the processors, the defect can cause unpredictable system behavior, including spurious errors such as application and system misbehavior, data corruption and data loss.

Intel is aware of the issue, describing it in its Errata documentation as follows:

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.”

A solution to the issue is said to be forthcoming, with the Debian advisory noting that a fix is available for Kaby Lake but is currently only available to system vendors, meaning that affected users should either contact vendors or see if the vendor may have already issued a patch. There is an “intel hyper-threading” patch for Skylake CPUs that fixes the issue but only models 78 and 94 and involves a fair level of technical knowledge to install.

In the meantime, Debian advises all users of Kaby Lake and Skylake CPUs to disable hyperthreading immediately via either BIOS or UEFI settings.

Image: ultramendoza/Flickr