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

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Message-ID: <20111228162653.GM17712@google.com>
Date:	Wed, 28 Dec 2011 08:26:53 -0800
From:	Tejun Heo <tj@...nel.org>
To:	Cyrill Gorcunov <gorcunov@...il.com>
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

Hello,

On Wed, Dec 28, 2011 at 08:18:09PM +0400, Cyrill Gorcunov wrote:
> Hi Tejun, thanks for comment! Yes, XOR is useless here in security meaning,
> but it simply breaks impression that these generating numbers "mean" somthing
> (I remained them as Vasily asked).

But that comes at the cost of creating the impression that the XOR
does something, which doesn't seem like a good situation.  e.g. Why do
we need per-domain XOR random keys for then?  That code now doesn't
mean anything.

> I personally fine to simply leave plain pointers here and root-only access
> since that is enough for us (and our tool will require root privileges
> anyway :)
> 
> OTOH, we could add some sha2 here with pointer+cookie as an initial value but I fear
> this will bring more code comlexity and computing sha2 hash is not that
> fast operation, which should be taken into account (note on x86-32 since
> pointers are 32bit values one could compute prehash for all space covered
> and if an attacker will know somehow cookie value the hash will be easily
> broken, not sure if it's really usefull for someone, since if you have root
> access to the machine such IDs will be the last thing attacker should be
> interested in :)

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?

> And it seems noone except us need this interface yet, so maybe sticking with
> "pointer exported under root-only" would be enough?

Maybe, dunno.  But even if it's gonna be raw pointer or XOR'd value
for now, I would suggest exporting it in the form which can be
replaced by proper hash in the future.  ie. Don't let userland assume
it's 32bit or 64bit value.

Thanks.

-- 
tejun
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