linux-kernel - Re: [PATCH] mm/x86: AMD Bulldozer ASLR fix

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Message-ID: <20150327123537.GB18912@pd.tnic>
Date:	Fri, 27 Mar 2015 13:35:38 +0100
From:	Borislav Petkov <bp@...en8.de>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Hector Marco-Gisbert <hecmargi@....es>,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Jan-Simon <dl9pf@....de>, linux-fsdevel@...r.kernel.org,
	kees Cook <keescook@...omium.org>,
	Ismael Ripoll <iripoll@...ca.upv.es>
Subject: Re: [PATCH] mm/x86: AMD Bulldozer ASLR fix

On Fri, Mar 27, 2015 at 01:14:48PM +0100, Ingo Molnar wrote:
> It's not a bug, it's a feature: to work around a Bulldozer cache
> aliasing performance problem we have to keep bits 12,13,14 equal for
> all mappings in the system.
>
> Your patch improves upon that fix: by per-boot randomizing the
> constant portion of the randomized range.

I have this one on the TODO list for today, I'll take care of those
formulations when applying.

> Btw., does anyone know how relevant the performance fix is these days?
> A simpler improvement would be to remove the workaround altogether and
> recover proper randomization of bits 12,13,14.

Nothing has changed with that respect in F15h, i.e. Bulldozer uarch. I
think we still need this workaround in place.

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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