On Friday, April 12, 2013 06:44:33 AM Josh Bressers wrote:
On Thu, Apr 11, 2013 at 12:54 PM, Reindl Harald
<h.reindl(a)thelounge.net>
wrote:
> which is exactly the goal ASLR is desigend for
It's designed to make certain types of attacks more difficult. It
doesn't make them impossible, just much harder.
Here is an example.
When you write a security exploit, you generally have to do things
like call into system libraries to do useful things. Generally you
have a limited amount of room for your exploit's "payload", so the
idea is to just leverage what the system can already do. Calling
system() would be an example of this. Now long ago, before things like
ASLR, if you had access to the binary you wanted to attack, you could
inspect the binary to see what the address of system() was. It didn't
change between runs of the binary, so I could hard code that address
into my exploit. With ASLR, every time you run the binary the address
of various system calls is now basically random (it's not exactly, but
that's an exercise for the reader to figure out).
I would like to point out that a non-PIE 64 bit application will only get 14
bits of randomization of the heap. In my opinion, this must be fixed since this
is very predictable. Even jemalloc provides 19 bits of heap randomization -
which is not ideal, but is better than our current default.
-Steve