Re: [patch 0/4] MAP_NOZERO v2 - VM_NOZERO/MAP_NOZERO early summer madness

[Andy Isaacson <adi@hexapodia.org>]

On Sat, Jun 30, 2007 at 08:21:52PM -0400, Kyle Moffett wrote:
> That's why you'd need to call an LSM hook to get a unique identifier,  
> as the LSM would actually need to allocate identifiers for  
> equivalence classes.  Secondly, processes may change labels as they  
> run, so you couldn't just call it once and cache the result, you  
> would need to call it for every freed page (or every re-use of a page).

Davide's patch adds a owner_uid field to mm_struct.  Assuming that turns
into a "mm security equivalence class identifier", the LSM can simply
update it when a label-change-event occurs.  No need to call out to
(potentially heavyweight!) LSM code in page allocation critical paths.

I'm a bit concerned that tracking the equivalence classes will get
expensive.  I think you can end up with quadratic explosion in the worst
case (every user using every permutation of LSM bits).

-andy