Re: [patch 1/4] Add routine for generating an ID for kernel pointer
From: Randy Dunlap
Date: Tue Dec 27 2011 - 18:48:54 EST
On 12/27/2011 03:33 PM, Andrew Morton wrote:
> On Fri, 23 Dec 2011 16:47:42 +0400
> Cyrill Gorcunov <gorcunov@xxxxxxxxxx> 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.
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