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

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Date:	Wed, 28 Dec 2011 20:53:36 +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 08:45:22AM -0800, Tejun Heo wrote:
> Hello,
> 
> On Wed, Dec 28, 2011 at 08:40:55PM +0400, Cyrill Gorcunov wrote:
> > > We have the whole crypto subsystem dealing with this.  It sure would
> > > be more complex than ^ operator but it's not like you have to open
> > > code the whole thing.  Is it really that complex to use?
> > 
> > No, Tejun, the use of crypto engine is not hard but it means more memory
> > consumption (one need to carry resulting hashes and print them out into
> > /proc) and more cpu consuption while we really need some fast and cheap
> > solution. Unlike other usage of crypto engine (such as encoding for net
> > layer, iirc ipsec uses it) I'm not really convinced we should use that
> > heavy artillery here ;)
> 
> But the cost would be attributed to the user requesting that specific
> data and given the amount of data to be hashed, I don't think the
> computational or memory overhead should be the deciding design factor
> here.  There are far more grave issues here.  Userland visible API and
> security.
>

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, 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.

> > I see, I could use some other form of output, it's not a problem. The main
> > problem which interface community prefer, should I really switch to crypto
> > usage or we can leave with root-only+plain-pointer approach?
> 
> I don't know either but if proper hashing (crypto or not) is simple
> enough, this really isn't a tradeoff we need to make, no?
> 

Hell knows, I would prefer to escape strong-crypto usage, but if there is
no other way, of course I'll change the approach ;)

	Cyrill
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