linux-kernel - Re: [PATCH 0/4] Checkpoint/Restore: Show in proc IDs of objects that can be shared between tasks

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Date:	Wed, 16 Nov 2011 10:19:23 +0400
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Matt Helsley <matthltc@...ibm.com>
Cc:	Pavel Emelyanov <xemul@...allels.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Glauber Costa <glommer@...allels.com>,
	Andi Kleen <andi@...stfloor.org>, Tejun Heo <tj@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 0/4] Checkpoint/Restore: Show in proc IDs of objects that
 can be shared between tasks

On Tue, Nov 15, 2011 at 09:44:27PM -0800, Matt Helsley wrote:
...
> > 
> > The object address is XOR-ed with a "random" value of the same size and then
> > shown in proc. Providing this poison is not leaked into the userspace then
> > ID seem to be safe.
> 
> Really? There's no way to quickly derive the random number from known
> allocation patterns and thereby break the obfuscation scheme?
> To start we can note that the low N bits are directly exposed in the ID
> of anything that requires 2^N-byte alignment.
> 
> I think it's really a question of whether the high order bits can be derived.
> 

Good point. I suppose we might use 2 random numbers here, one for xor and
second to shuffle bits.

> And of course the random number only needs to be derived once per boot
> before it reveals the address of everything with an ID.

	Cyrill
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