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From: Pavel Machek <pavel@ucw.cz>
To: Jakub Jelinek <jakub@redhat.com>
Cc: Ingo Molnar <mingo@elte.hu>, Jiri Kosina <jkosina@suse.cz>,
	Andrew Morton <akpm@osdl.org>, "Rafael J. Wysocki" <rjw@sisk.pl>,
	kernel list <linux-kernel@vger.kernel.org>,
	Abel Bernabeu <abel.bernabeu@gmail.com>,
	Hugh Dickins <hugh@veritas.com>,
	Arjan van de Ven <arjan@infradead.org>
Subject: Re: [regression] Re: brk randomization breaks columns
Date: Tue, 5 Feb 2008 17:18:10 +0100	[thread overview]
Message-ID: <20080205161810.GF24331@elf.ucw.cz> (raw)
In-Reply-To: <20080205130546.GF30691@devserv.devel.redhat.com>

On Tue 2008-02-05 08:05:46, Jakub Jelinek wrote:
> On Tue, Feb 05, 2008 at 01:54:26PM +0100, Ingo Molnar wrote:
> > * Jiri Kosina <jkosina@suse.cz> wrote:
> > 
> > > On Tue, 5 Feb 2008, Pavel Machek wrote:
> > > 
> > > > > Actually, this clearly shows that either prehistoric libc.so.5 or the 
> > > > > program itself are broken.
> > > > I believe it shows clear regression in latest 2.6.25 kernel.
> > > 
> > > I am still not completely sure. It might be a regression, but it also 
> > > might just trigger the bug in ancient version in libc.so.5 which might 
> > > be fixed in some later version [...]
> > 
> > which too is a regression ...
> > 
> > really, lets add a sysctl for this, and a .config option that either 
> > disables or enables it. Then we will default to disabled. (but users can 
> > enable it - and distros can build their kernels with this .config option 
> > enabled)
> 
> I don't think kernel should care about programs which are buggy and make invalid
> assumptions, and that's the case here.  I remember we have been

Those "invalid assumptions" crept into documentation. Everybody knew
heap starts at the end of bss in 1995.

> 5 years ago when brk randomization has been added to Red Hat kernels.  There was
> one or two broken programs which made assumptions on what brk(0) is supposed
> to return at program startup, everything else was ok.

That's not the problem. Problem is that programs assume
brk(0x12345678) allocates space between end of bss and 0x12345678;
which is no longer the case.

And actually even
http://opengroup.org/onlinepubs/007908775/xsh/brk.html only talks
about "ammount of space"... implying begging of that space is well
known.

								Pavel
PS: It would be nice to fix linux man pages to say that it brk() moves
end of the heap, only, and that any usage of brk() is invalid w/o
doing brk(0) before.

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

  reply	other threads:[~2008-02-05 16:18 UTC|newest]

Thread overview: 39+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-02-04 12:28 Pavel Machek
2008-02-04 13:01 ` Ingo Molnar
2008-02-04 13:28   ` Pavel Machek
2008-02-04 14:55     ` Jiri Kosina
2008-02-04 20:25       ` Pavel Machek
2008-02-04 14:33   ` Jiri Kosina
2008-02-04 16:12     ` Jiri Kosina
     [not found]       ` <15577be70802041016m97cddbfk43b9073408bcbce9@mail.gmail.com>
     [not found]         ` <15577be70802041029o2975ba6do34589bbdc81d1652@mail.gmail.com>
2008-02-04 19:52           ` Fwd: " Pavel Machek
2008-02-04 21:54             ` Abel Bernabeu
2008-02-04 22:48               ` Jiri Kosina
2008-02-04 23:13                 ` Abel Bernabeu
2008-02-04 23:39                   ` Pavel Machek
2008-02-04 20:31       ` Pavel Machek
2008-02-05  1:57 ` Jiri Kosina
2008-02-05 11:06   ` [regression] " Pavel Machek
2008-02-05 12:50     ` Jiri Kosina
2008-02-05 12:54       ` Ingo Molnar
2008-02-05 13:05         ` Jakub Jelinek
2008-02-05 16:18           ` Pavel Machek [this message]
2008-02-05 16:37             ` Ingo Molnar
2008-02-05 16:12       ` Pavel Machek
2008-02-05 13:08   ` Hugh Dickins
2008-02-05 15:00     ` Arjan van de Ven
2008-02-05 15:46       ` Pavel Machek
2008-02-05 15:49         ` Jiri Kosina
2008-02-05 15:55           ` Pavel Machek
2008-02-05 15:49         ` Ingo Molnar
2008-02-05 15:59           ` Pavel Machek
2008-02-05 16:06             ` Ingo Molnar
2008-02-05 22:03               ` Pavel Machek
2008-02-05 16:58         ` Arjan van de Ven
2008-02-05 17:33           ` Pavel Machek
2008-02-05 22:35           ` Jiri Kosina
2008-02-06  3:24             ` Randy Dunlap
2008-02-05 16:02   ` Pavel Machek
2008-02-05 16:09     ` Ingo Molnar
2008-02-05 22:04       ` Pavel Machek
2008-02-05 18:05   ` Pavel Machek
2008-02-05 20:42     ` Jiri Kosina

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