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

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Message-ID: <20150327121448.GB15631@gmail.com>
Date:	Fri, 27 Mar 2015 13:14:48 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Hector Marco-Gisbert <hecmargi@....es>
Cc:	Borislav Petkov <bp@...en8.de>, 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


* Hector Marco-Gisbert <hecmargi@....es> wrote:

> A bug in Linux ASLR implementation which affects some AMD processors 
> has been found. The issue affects to all Linux process even if they 
> are not using shared libraries (statically compiled).

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.

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.

Thanks,

	Ingo
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