Date: Fri, 29 Apr 2005 06:20:53 -0700
From: Andrew Morton <akpm@osdl.org>
To: Hubert Tonneau <hubert.tonneau@fullpliant.org>
Cc: linux-kernel@vger.kernel.org, Arjan van de Ven <arjanv@redhat.com>
Subject: Re: 2.6.12-rc3 mmap lack of consistency among runs
Message-Id: <20050429062053.2c9943ce.akpm@osdl.org>
In-Reply-To: <0563I2L12@server5.heliogroup.fr>
References: <0563I2L12@server5.heliogroup.fr>
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Hubert Tonneau <hubert.tonneau@fullpliant.org> 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.

Dunno.

> 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 ?

MAP_FIXED?
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