Re: [PATCH] [RFC] Introduce mmap randomization

From	Pavel Machek <pavel@ucw.cz>
Newsgroups	linux.kernel
Subject	Re: [PATCH] [RFC] Introduce mmap randomization
Date	2016-08-14 18:30 +0200
Message-ID	<s66sp-1Uu-17@gated-at.bofh.it> (permalink)
References	<rZfh8-5uR-9@gated-at.bofh.it> <rZfh8-5uR-19@gated-at.bofh.it>
Organization	linux.* mail to news gateway

Show all headers | View raw

On Tue 2016-07-26 11:22:26, william.c.roberts@intel.com wrote:
> From: William Roberts <william.c.roberts@intel.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

Back to linux.kernel | Previous | Next | Find similar | Unroll thread

Thread

Re: [PATCH] [RFC] Introduce mmap randomization Pavel Machek <pavel@ucw.cz> - 2016-08-14 18:30 +0200

csiph-web