Date: Thu, 27 Jan 2005 20:11:20 +0100
From: Ingo Molnar <mingo@elte.hu>
To: Pavel Machek <pavel@ucw.cz>
Cc: Arjan van de Ven <arjan@infradead.org>, linux-kernel@vger.kernel.org,
       akpm@osdl.org, torvalds@osdl.org
Subject: Re: Patch 1/6  introduce sysctl
Message-ID: <20050127191120.GA10460@elte.hu>
References: <20050127101117.GA9760@infradead.org> <20050127101201.GB9760@infradead.org> <20050127181525.GA4784@elf.ucw.cz>
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* Pavel Machek <pavel@ucw.cz> wrote:

> Hi!
> 
> > This first patch of the series introduces a sysctl (default off) that
> > enables/disables the randomisation feature globally. Since randomisation may
> > make it harder to debug really tricky situations (reproducability goes
> > down), the sysadmin needs a way to disable it globally.
> 
> Well, for distribution vendors, seeing "these reports from users are
> same error" will becoe harder, too, and sysctl can not help there :-(.

this is true to a limited degree, but it's only part of the picture. 
When we first introduced address-space randomisation in Fedora 1 (almost
2 years ago) we were worried about this effect too, very much in fact. 

What happened is that the _debugging infrastructure_ improved. Fedora
introduced debug-info packages, so that we dont get any raw dumps of
bugs anymore - what we get are nice symbolic backtraces which are easy
to match up against each other.

also, we already have this effect in the mainline kernel - on P4's the
stack is already randomized. Also, prelink (even the non-randomized
variant) already creates a per-machine VM layout of libraries.

so, i'm glad to report, it's a non-issue. Sometimes developers want to
disable randomisation during development (quick'n'easy hacks get quicker
and easier - e.g. if you watch an address within gdb), so having the
capability for unprivileged users to disable randomisation on the fly is
useful and Fedora certainly offers that, but from a support and
bug-reporting POV it's not a problem.

	Ingo
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