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Date: Thu, 11 Aug 2011 10:54:58 -0400
From: Rich Felker <>
Subject: Re: malloc and linux memory layout

On Thu, Aug 11, 2011 at 11:43:05AM +0400, Vasiliy Kulikov wrote:
> > The mmap zone (where mmaps are put by
> > default) starts just below the stack limit and continues downward as
> > more mappings are made.
> Not only this zone.  mmap() can return address before main program text if
> there is enough space there.


> Other minor (Linux-specific) things:
> Low unmappable pages region might be absent if the task has CAP_SYS_RAWIO
> capability.  But pages before mmap_min_addr will be mmap'ed only by
> explicit mmap(addr, ..., MAP_FIXED, ...), no libs will be there.

This is mostly irrelevant since it requires root or equivalent.
(CAP_SYS_RAWIO might as well be root since it lets you exploit
kernelspace null pointer dereference bugs to get root).

> "Reserved for kernelspace use" region might be absent too for 32-bit
> tasks running on 286-64 system.



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