linux-kernel - Linux on Intel x86: How to disable Hyperthreading

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Date:   Sat, 23 Jun 2018 12:57:18 +0200
From:   Martin Steigerwald <martin@...htvoll.de>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org
Subject: Linux on Intel x86: How to disable Hyperthreading

Cc´d people for X86 architecture in MAINTAINERS.


Hi!

According to

https://www.kuketz-blog.de/tlbleed-neue-sicherheitsluecken-bei-intel-cpus/

in

https://www.blackhat.com/us-18/briefings/schedule/#tlbleed-when-protecting-your-cpu-caches-is-not-enough-10149

(Firefox and Chromium with current settings and add-ons webbrowsers do 
not display the contents of the page)

one can read:

> Our TLBleed exploit successfully leaks a 256-bit EdDSA key from
> libgcrypt (used in e.g. GPG) with a 98% success rate after just a
> single observation of signing operation on a co-resident hyperthread
> and just 17 seconds of analysis time..


And this probably would explain the disabling of it in OpenBSD.

What is your take on this?


Also how would you disable it in case you would?

I currently test run with the script I found on:

https://serverfault.com/questions/235825/disable-hyperthreading-from-within-linux-no-access-to-bios

Just to see whether I notice a significant performance drop.

Thanks.
-- 
Martin