Re: x86: randomize brk() and RLIMIT_DATA

[Arjan van de Ven <arjan@infradead.org>]

On Thu, 25 Oct 2007 16:41:24 +0300
Sami Farin <safari-kernel@safari.iki.fi> wrote:

> Would be neat if randomized brk and setrlimit(RLIMIT_DATA, ...)
> worked in a predictable way:

this isn't a valid case afaics; even on "traditional x86" (before we
changed the address space layout, or even today if you have an
unlimited stack rlimit) this isn't going to work. applications really
shouldn't use (s)brk() but malloc(); you have to be able to fall back
to mmap regardless of what you do.

> 
> $ gcc brk.c -fPIC -pie -m64;./a.out;./a.out;./a.out
> sbrk=0x7f721b815000 main=0x7f721af04860
> sbrk succeeded (brk=0x7f721b909240)
> sbrk=0x7fc3d77e2000 main=0x7fc3d66fa860
> sbrk failed: Cannot allocate memory (brk=0x7fc3d77e2000)
> sbrk=0x7f05b0615000 main=0x7f05af76b860
> sbrk failed: Cannot allocate memory (brk=0x7f05b0615000)
> 


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