Subject: Re: [PATCH 1/4] [x86] Add command line option to enable/disable
	hyper-threading.
From: Ben Collins <ben.collins@ubuntu.com>
To: Arjan van de Ven <arjan@infradead.org>
Cc: Pavel Machek <pavel@ucw.cz>, linux-kernel@vger.kernel.org,
       torvalds@osdl.org
In-Reply-To: <1164989436.3233.85.camel@laptopd505.fenrus.org>
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Date: Fri, 01 Dec 2006 11:14:02 -0500
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On Fri, 2006-12-01 at 17:10 +0100, Arjan van de Ven wrote:
> > 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.

Thanks for clearing that up. Patch withdrawn.
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