Re: [PATCH] x86: Enable full randomization on i386 and X86_32.

From: Ingo Molnar
Date: Fri Mar 11 2016 - 03:51:29 EST

* Hector Marco-Gisbert <hecmargi@xxxxxx> 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@xxxxxx>
> Signed-off-by: Ismael Ripoll Ripoll <iripoll@xxxxxx>

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.