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Serious Intel Skylake and Kaby Lake microcode bug unearthed

by Mark Tyson on 26 June 2017, 10:11

Tags: Intel (NASDAQ:INTC)

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Over the weekend an Intel processor microcode bug was highlighted with a warning advisory via the Debian.org mailing lists. Henrique de Moraes Holschuh warned that systems equipped with Intel Skylake and Kaby Lake processors could "in some situations, dangerously misbehave when hyper-threading is enabled." The errant behaviour could include "application and system misbehavior, data corruption, and data loss," all of which are serious for practical computer use.

The Debian advisory says there's a simple fix to prevent any dangerous misbehaviour by your Skylake or Kaby Lake processor - disable Hyperthreading. Processors affected include Core processors for desktops and laptops, and Intel Xeon processors. Basically if it is from one of those families and it has Hyperthreading capabilities then it is affected.

Intel updated its processors documentation with a new errata (PDF) note a couple of months ago and that was due to these bugs being discovered. One official explanation of the issue is as follows:

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 (eg RAX, EAX or AX for AH) may cause unpredictable system behaviour. This can only happen when both logical processors on the same physical processor are active.

The Debian Mailing list post says that the microcode bug has been noted as affecting some of its OS users. It notes that other OS users are likely to be impacted too, not just Linux based OS users.

So what if you own one of Intel's 6th to 7th generation processors with Hyperthreeading? Debian recommends you disable Hyperthreading for now until a UEFI/BIOS update is issued by your motherboard vendor. Some Skylake users will be able to update the intel-hyperthreading package themselves. Instructions are available about half way down the Debian mailing list post.

HEXUS Forums :: 20 Comments

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Ooops that's a pretty spectacular bug there…
I'll stick with my Haswell-E for the time being.
If this bug affects Skylake and is so serious, why did it take so long to find? Hm.
Ooops that's a pretty spectacular bug there…

It's certainly spectacular but it can't be very obvious or prevalent as it seems to have gone unnoticed for ages.
It's certainly spectacular but it can't be very obvious or prevalent as it seems to have gone unnoticed for ages.

Alternatively it's been crashing for ages but it's taken this long to rule out the OS, drivers, programmes running, data errors, viruses, malware etc and pinpoint the Unicode as a problem.

If you had a crash every time you tried to use a pivot table in Excel (as an example I know that isn't the fault described here,) on a Windows 10 machine how many guesses at the cause would it take before you got to the CPU microcode?