linux-kernel - Re: [PATCH] x86: Enable full randomization on i386 and X86

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Message-ID: <20160311085108.GA29750@gmail.com>
Date:	Fri, 11 Mar 2016 09:51:08 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Hector Marco-Gisbert <hecmargi@....es>
Cc:	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,
	kees Cook <keescook@...omium.org>,
	Ismael Ripoll Ripoll <iripoll@....es>
Subject: Re: [PATCH] x86: Enable full randomization on i386 and X86_32.


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

> Currently on i386 and on X86_64 when emulating X86_32 in legacy mode, only
> the stack and the executable are randomized but not other mmapped files
> (libraries, vDSO, etc.). This patch enables randomization for the
> libraries, vDSO and mmap requests on i386 and in X86_32 in legacy mode. 
> 
> By default on i386 there are 8 bits for the randomization of the libraries,
> vDSO and mmaps which only uses 1MB of VA.
> 
> This patch preserves the original randomness, using 1MB of VA out of 3GB or
> 4GB. We think that 1MB out of 3GB is not a big cost for having the ASLR.
> 
> The first obvious security benefit is that all objects are randomized (not
> only the stack and the executable) in legacy mode which highly increases
> the ASLR effectiveness, otherwise the attackers may use these
> non-randomized areas. But also sensitive setuid/setgid applications are
> more secure because currently, attackers can disable the randomization of
> these applications by setting the ulimit stack to "unlimited". This is a
> very old and widely known trick to disable the ASLR in i386 which has been
> allowed for too long.
> 
> Another trick used to disable the ASLR was to set the ADDR_NO_RANDOMIZE
> personality flag, but fortunately this doesn't work on setuid/setgid
> applications because there is security checks which clear Security-relevant
> flags. 
> 
> This patch always randomizes the mmap_legacy_base address, removing the
> possibility to disable the ASLR by setting the stack to "unlimited".
> 
> 
> Signed-off-by: Hector Marco-Gisbert <hecmargi@....es>
> Signed-off-by: Ismael Ripoll Ripoll <iripoll@....es>

This signoff line is not valid (primary author is first SOB line, patch submitted 
is last SOB line), I've changed the second Signed-off-by to an Acked-by.

Thanks,

	Ingo