linux-kernel - Re: [PATCH] [RFC] Introduce mmap randomization

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Message-ID: <20160814162226.GA7583@amd>
Date:	Sun, 14 Aug 2016 18:22:26 +0200
From:	Pavel Machek <pavel@....cz>
To:	william.c.roberts@...el.com
Cc:	jason@...edaemon.net, linux-mm@...r.kernel.org,
	linux-kernel@...r.kernel.org, kernel-hardening@...ts.openwall.com,
	akpm@...ux-foundation.org, keescook@...omium.org,
	gregkh@...uxfoundation.org, nnk@...gle.com, jeffv@...gle.com,
	salyzyn@...roid.com, dcashman@...roid.com
Subject: Re: [PATCH] [RFC] Introduce mmap randomization

On Tue 2016-07-26 11:22:26, william.c.roberts@...el.com wrote:
> From: William Roberts <william.c.roberts@...el.com>
> 
> This patch introduces the ability randomize mmap locations where the
> address is not requested, for instance when ld is allocating pages for
> shared libraries. It chooses to randomize based on the current
> personality for ASLR.
> 
> Currently, allocations are done sequentially within unmapped address
> space gaps. This may happen top down or bottom up depending on scheme.
> 
> For instance these mmap calls produce contiguous mappings:
> int size = getpagesize();
> mmap(NULL, size, flags, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x40026000
> mmap(NULL, size, flags, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x40027000
> 
> Note no gap between.
> 
> After patches:
> int size = getpagesize();
> mmap(NULL, size, flags, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x400b4000
> mmap(NULL, size, flags, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x40055000
> 
> Note gap between.

Ok, I guess you can do it... but... what will be the effect on
available address space for a process? By doing this, won't you
fragment it horribly? This might be nasty on 32-bit systems...

Best regards,
								Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html