linux-kernel - Re: [patch 1/4] Add routine for generating an ID for kernel pointer

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Date:	Wed, 28 Dec 2011 21:14:19 +0400
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	linux-kernel@...r.kernel.org,
	Pavel Emelyanov <xemul@...allels.com>,
	Glauber Costa <glommer@...allels.com>,
	Andi Kleen <andi@...stfloor.org>,
	Matt Helsley <matthltc@...ibm.com>,
	Pekka Enberg <penberg@...nel.org>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Vasiliy Kulikov <segoon@...nwall.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Alexey Dobriyan <adobriyan@...il.com>
Subject: Re: [patch 1/4] Add routine for generating an ID for kernel pointer

On Wed, Dec 28, 2011 at 09:01:16AM -0800, Tejun Heo wrote:
> Hello,
> 
> On Wed, Dec 28, 2011 at 08:53:36PM +0400, Cyrill Gorcunov wrote:
> > Well, it is not deciding but it should be taken into account. One could
> > be reading this IDs again and again and again affecting performance of
> > the whole system,
> 
> I can't see how it would affect performance of the whole system.
> Calculating hash doesn't involve any further locking or use of scarce
> global resource.  It would add small amount memory and processing
> overhead for the task reading the hash.  It sure is something to be
> considered but I really don't think this should be a major factor
> here.
> 

Yeah, indeed.

> > which means I really would prefer to limit access to such
> > features (ie root-only). If (as I said) for other cases there is simply no way to
> > _not_ use crypto, our case might be the one where using crypto is redundant.
> 
> Limiting it to root and just exporting printer (or maybe XOR with a
> randomish value) may be good enough.  I don't know.  However, we no
> longer consider exporting pointers to unpriviliedged userland safe and
> this can be useful in many circumstances, so if it's not too
> difficult, I think trying to use proper hash would be nide.

OK, Tejun, I'll try, but no promises :) Thanks!

	Cyrill
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