Re: 2.6.12-rc3 mmap lack of consistency among runs

From: Andrew Morton
Date: Fri Apr 29 2005 - 08:30:18 EST

Hubert Tonneau <hubert.tonneau@xxxxxxxxxxxxxx> wrote:
> Andrew Morton wrote:
> >
> > Maybe you're being bitten by the address space randomisation.
> >
> > Try
> > echo 0 > /proc/sys/kernel/randomize_va_space
> Ok, it solves my issue, but:
> . desabling it through 'echo 0 > /proc/sys/kernel/randomize_va_space' is not
> a solution because only the application knows that it wants it to be desabled,
> and the application is not root so cannot write to /proc; morever the
> application can only speak for itself so desabling should be on a per process
> bias.

You can disable randomization on a per-executable basis by setting an ELF
personality. I forget the magic incantation. Arjan?

> I can hardly imagine to publish a warning in the README such as:
> This software only works if your Linux kernel is configured so that
> /proc/sys/kernel/randomize_va_space = 0
> . second, my process restart succeeding roughly in 50% cases means that the
> randomisation performed is just a toy. A virus assuming fixed memory layout
> will still succeed 50% of times to install.


> All in all, I'm not concerned about Linux kernel to randomise or not,
> but I need to have a reliable way to request a memory region and be granted
> that I can request the same one in a futur run.
> What is the proper way to get such a memory area ?

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