Messages in this thread | | | Date | Sat, 18 Feb 2012 20:35:56 +0400 | From | Vasiliy Kulikov <> | Subject | Re: [kernel-hardening] Re: Add overflow protection to kref |
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On Sat, Feb 18, 2012 at 11:15 -0500, David Windsor wrote: > On Fri, Feb 17, 2012 at 8:44 PM, Roland Dreier <roland@purestorage.com> wrote: > > On Fri, Feb 17, 2012 at 3:39 PM, Djalal Harouni <tixxdz@opendz.org> wrote: > >>> 2) what to do with architectures-loosers? > >> There is lib/atomic64.c but with a static hashed array of raw_spinlocks. > > > > Even leaving aside performance impact of atomic64_t (and probably > > in most cases the performance of kref is not important at all), it is > > unfortunate to bloat the size from 4 bytes to 8 bytes. > > > > It seems much better to have some out-of-line code for overflow > > checking rather than increasing the size of every data structure > > that embeds a kref. > > > > kref is mostly a set of operations (init, get, sub, put) to be > performed on an atomic_t object. > > >From linux/kref.h: > > struct kref { > atomic_t refcount; > }; > > Moving overflow protection into kref amounts to placing some > procedural code into kref_get and kref_sub, adding a rather small > constant factor of time, not space, to users of kref. Introducing > overflow protection doesn't necessitate adding anything to kref for > greater state tracking. > > Did you have something else in mind when you suggested a potential > increase in the size of kref?
4 bytes => 8 bytes of atomic_t => atomic64_t in case we increase the refcounter range to make it impossible to overflow the refcounter
compared to
add checks into kref_get()/atomic_inc*() without changing refcounter ranges.
Thanks,
-- Vasiliy Kulikov http://www.openwall.com - bringing security into open computing environments
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