[uClibc] Re: malloc in uclibc

[Peter S. Mazinger]

On Tue, 9 Mar 2004, Peter S. Mazinger wrote:

> Hello!
> 
> The PaX project (pax.grsecurity.net) provides heap randomization, but the 
> malloc implementation of uClibc does not work with it (tested w/ 
> malloc-standard). I copied 2 messages from the pax developer:
> 
> 1.
> ok, after some debugging i think this caused by uclibc and its
> malloc implementation, i haven't checked that code but it seems
> it doesn't use brk(0) to learn the beginning of the brk() region
> but something else, my bet is that it simply takes the _end symbol
> and rounds it up to be 16 byte aligned. it's probably a feature
> but unfortunately it makes brk() randomization pointless as well
> under uclibc - you may want to bring this to the developers'
> attention.
> 
> 2.
> i've quickly grepped through this code and i can't really tell from
> that which malloc() implementation is the best (for randomization),
> in fact, i had the impression that none of them is as they they
> don't seem be to doing a sbrk(0) at all on startup (which is how glibc
> learns the beginning of the randomized heap). you could verify this
> by simply compiling your uclibc with all 3 versions and run paxtest
> on them, i think none of them will show heap randomization. in that
> case you should probably talk to the uclibc developers to consider
> using sbrk(0) instead of _end to derive the beginning of the heap.
> note that this however breaks some unix tradition (at least that's
> what i read on a fedora list last november) and some apps may not
> work properly, like some lisp stuff which apparently assumed that
> _end == sbrk(0) on startup.

I have checked the other 2 malloc options to see where the heap 
randomization works. MALLOC works (although the help says, it does not 
use brk(), only mmap() ), MALLOC_SIMPLE does not work (at least this is 
what paxtest shows).

Peter

-- 
Peter S. Mazinger <ps dot m at gmx dot net>           ID: 0xA5F059F2
Key fingerprint = 92A4 31E1 56BC 3D5A 2D08  BB6E C389 975E A5F0 59F2


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