linux-kernel - Re: [PATCH v4 10/10] x86-64: Add CONFIG_UNSAFE

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Date:	Tue, 31 May 2011 20:57:27 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Andi Kleen <andi@...stfloor.org>
cc:	Andy Lutomirski <luto@....EDU>, Ingo Molnar <mingo@...e.hu>,
	x86@...nel.org, linux-kernel@...r.kernel.org,
	Jesper Juhl <jj@...osbits.net>, Borislav Petkov <bp@...en8.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Jan Beulich <JBeulich@...ell.com>,
	richard -rw- weinberger <richard.weinberger@...il.com>,
	Mikael Pettersson <mikpe@...uu.se>
Subject: Re: [PATCH v4 10/10] x86-64: Add CONFIG_UNSAFE_VSYSCALLS to
 feature-removal-schedule

On Tue, 31 May 2011, Andi Kleen wrote:
> > +What:	CONFIG_UNSAFE_VSYSCALLS (x86_64)
> > +When:	When glibc 2.14 or newer is ubitquitous.  Perhaps mid-2012.
> > +Why:	Having user-executable code at a fixed address is a security problem.
> > +	Turning off CONFIG_UNSAFE_VSYSCALLS mostly removes the risk but will
> > +	make the time() function slower on glibc versions 2.13 and below.
> 
> I disagree with this description (and the whole idea really)
> 
> First it's time+gettimeofday+vgetcu, not just time.
> 
> A more accurate description is 
> 
> "will make all x86-64 Linux programs written to the original pre
> vDSO syscall ABI significantly slower"
> 
> And the assumption that all world is using glibc is still as bad
> as it was on the first po.st
> 
> And it's still a bad idea. Especially since there's a much better
> alternative anyways for the "security problem" which has none of 
> these drawbacks.

How about posting an alternative patch?

Thanks,

	tglx
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