Subject: Re: [PATCH 1/4] [x86] Add command line option to enable/disable
	hyper-threading.
From: Arjan van de Ven <arjan@infradead.org>
To: Ben Collins <ben.collins@ubuntu.com>
Cc: Pavel Machek <pavel@ucw.cz>, linux-kernel@vger.kernel.org,
       torvalds@osdl.org
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	 <1164985757.5257.933.camel@gullible>
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Organization: Intel International BV
Date: Fri, 01 Dec 2006 17:10:36 +0100
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> I'm just basing this on the history of the patch, which preceeds me, so
> if this is incorrect, please don't blame me for misinformation :)
> 
> The original patch claims that hyper-threading opens the user up to some
> sort of security risk involving hardware limitations in protecting
> memory across the threads. I can't recall all the details.
> 
> If this is wrong, I'm more than happy to just drop the whole damn patch.

that is not correct.
I suspect what is meant is the "attack" on older openssl versions where
you could in theory get SOME information about a key in use by snooping
cache patterns in a shared cache situation. By no means is it a "direct"
leak of any kind, and openssl has since then been fixed to not have as
many key-dependent execution streams anymore.

I would suggest you drop the patch; openssl has been long fixed, and it
was only a theoretical attack in the first place...
I'm not saying the attack isn't something that should be addressed.. but
it is, and disabling hyperthreading is not the right fix.


-- 
if you want to mail me at work (you don't), use arjan (at) linux.intel.com
Test the interaction between Linux and your BIOS via http://www.linuxfirmwarekit.org

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