Follow @Openwall on Twitter for new release announcements and other news
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date: Tue, 09 Dec 2014 22:09:02 -0500
From: Steve Grubb <>
Cc: Daniel Micay <>
Subject: Re: Offset2lib: bypassing full ASLR on 64bit Linux

On Tuesday, December 09, 2014 08:03:10 PM Daniel Micay wrote:
> On 09/12/14 11:18 AM, Steve Grubb wrote:
> > 4) Then I started wondering about the heap when you use other memory
> > manager libraries such as jemalloc. This turned out to be interesting.
> > You get about 19 bits of randomness using it. Its not as bad as non-PIE
> > glibc but not as good as PIE glibc. You also got the same amount of
> > randomness whether the app was PIE or not. This is an area ripe for more
> > experimenting, exploiting, and patching. Supposedly some of these heap
> > managers use mmap as the underlying allocator. So, why aren't they
> > getting 29 bits, too? :-)
> Your measurement of the difference is quite accurate.

There's other allocators, too.

$ ./all-bits 
heap       14 bits
pie-heap   29 bits

$ ./all-bits 
heap       25 bits
pie-heap   25 bits

Different allocators, different strategies, different randomness. While people 
are thinking about this, it might be a good time to check everything that's 
popular. that I think about it, I haven't looked for address bias 
in the last samples....  :-)


> The page multiple constraint zaps 12 potential bits of entropy, but
> jemalloc's 4M chunk alignment increases that to 22 bits. I'm not sure
> what can be done about it because there's a very strong performance case
> for the design.
> I sent in a fix for the MALLOC_CONF part of this at least, so an
> attacker won't be able to reduce it further:

Download attachment "signature.asc" of type "application/pgp-signature" (182 bytes)

Powered by blists - more mailing lists

Please check out the Open Source Software Security Wiki, which is counterpart to this mailing list.

Confused about mailing lists and their use? Read about mailing lists on Wikipedia and check out these guidelines on proper formatting of your messages.