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

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Message-ID: <4EFA6751.3060502@xenotime.net>
Date:	Tue, 27 Dec 2011 16:48:17 -0800
From:	Randy Dunlap <rdunlap@...otime.net>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	Cyrill Gorcunov <gorcunov@...nvz.org>,
	linux-kernel@...r.kernel.org,
	Pavel Emelyanov <xemul@...allels.com>,
	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>
Subject: Re: [patch 1/4] Add routine for generating an ID for kernel pointer

On 12/27/2011 03:33 PM, Andrew Morton wrote:
> On Fri, 23 Dec 2011 16:47:42 +0400
> Cyrill Gorcunov <gorcunov@...nvz.org> wrote:
> 
>> The routine XORs the given pointer with a random value
>> producing an ID (32 or 64 bit, depending on the arch).
>>
>> Since it's a valuable information -- only CAP_SYS_ADMIN
>> is allowed to obtain it.
>>
>>  - Tejun worried about the single poison value was a weak side -
>>    leaking one makes all the IDs vulnerable. To address this
>>    several poison values - one per object type - are introduced.
>>    They are stored in a plain array.
>>  - Pekka proposed to initialized poison values in the late_initcall callback
>>  - ... and move the code to mm/util.c
>>
>> ...
>>
> 
> The code in general looks simple and reasonable to me.  I'm too much of
> a security weenie to pass judgement on the security aspects.
> 
>>
>> ...
>>
>> --- linux-2.6.git.orig/mm/Kconfig
>> +++ linux-2.6.git/mm/Kconfig
>> @@ -373,3 +373,19 @@ config CLEANCACHE
>>  	  in a negligible performance hit.
>>  
>>  	  If unsure, say Y to enable cleancache
>> +
>> +config GENERIC_OBJECT_ID
>> +	bool "Enable generic object ID infrastructure"
>> +	depends on CHECKPOINT_RESTORE
> 
> Is c/r useless without GENERIC_OBJECT_ID?  If so, perhaps a `select'
> would be good here.

Is GENERIC_OBJECT_ID useful elsewhere?  If so, then it shouldn't depend
on CHECKPOINT_RESTORE -- it should just live in lib/ instead of in mm/
and CHECKPOINT_RESTORE should select it.

>> +	default n
>> +	help
>> +	  Turn on the functionality that can generate IDs for kernel
>> +	  objects, which are exported to userspace via /proc filesystem.
>> +
>> +	  It is useful if you need to examinate kernel objects and test
>> +	  if they are shared between several tasks. These IDs should never
>> +	  be used for anything but the "sameness" test. Besides, the IDs are
>> +	  dynamic and valid only while object is alive, once it get freed or
>> +	  kernel is rebooted -- the IDs will be changed.
>> +
>> +	  If unsure, say N here.


-- 
~Randy
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