linux-kernel - Re: + syscalls-x86-add-__nr_kcmp-syscall-v8.patch added to -mm tree

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Message-ID: <20120410234206.GA19251@redhat.com>
Date:	Wed, 11 Apr 2012 01:42:06 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Cyrill Gorcunov <gorcunov@...nvz.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Pavel Emelyanov <xemul@...allels.com>,
	Andrey Vagin <avagin@...nvz.org>,
	KOSAKI Motohiro <kosaki.motohiro@...il.com>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Glauber Costa <glommer@...allels.com>,
	Andi Kleen <andi@...stfloor.org>, Tejun Heo <tj@...nel.org>,
	Matt Helsley <matthltc@...ibm.com>,
	Pekka Enberg <penberg@...nel.org>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Vasiliy Kulikov <segoon@...nwall.com>,
	Alexey Dobriyan <adobriyan@...il.com>, Valdis.Kletnieks@...edu,
	Michal Marek <mmarek@...e.cz>,
	Frederic Weisbecker <fweisbec@...il.com>,
	linux-kernel@...r.kernel.org, Jonathan Corbet <corbet@....net>
Subject: Re: + syscalls-x86-add-__nr_kcmp-syscall-v8.patch added to -mm tree

On 04/10, H. Peter Anvin wrote:
>
> On 04/10/2012 04:08 PM, Oleg Nesterov wrote:
> >
> > OK, since this is discussed again...
> >
> > Can this comment can also explain why do we obfuscate the pointers
> > by type? I mean, I don't really understand why the one-dimensional
> > cookies[2] is "not enough" from security pov.
>
> Because it's cheap.  "Just enough" is not what you want to shoot for,
> ever, you want to get past the "just enough" point and then consider
> "what can I get for cheap at this point"?

OK, I am not arguing. Just I thought that the small note like
"we are doing this per-type to obfuscate even more" can help.
I wouldn't have asked, but Cyrill rewrites this comment anyway.

Perhaps this is just me, but my first (and wrong) impression was
that somehow this is needed for correctness.

Oleg.

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