Re: [kernel-hardening] [RFC v3 PATCH 01/13] Add architecture independent hardened atomic base

[Colin Vidal <colin@cvidal.org>]

On Tue, 2016-11-01 at 14:55 +0200, Hans Liljestrand wrote:
> On Tue, Nov 01, 2016 at 12:15:25PM +0000, Reshetova, Elena wrote:
> > 
> > > 
> > > Hi (again :-)) Elena, Hans,
> > 
> > > 
> > > diff --git a/include/linux/atomic.h b/include/linux/atomic.h
> > <snip>
> > > 
> > > +#ifndef atomic_cmpxchg_wrap
> > > +#define  atomic_cmpxchg_wrap(...)				\
> > > +	__atomic_op_fence(atomic_cmpxchg_wrap, __VA_ARGS__) #endif
> > >  #endif /* atomic_cmpxchg_relaxed */
> > > 
> > 
> > > 
> > > I have a problem here. With ARMv7 (without any of my patches), I have a
> > > implicit declaration of atomic_cmpxchg_wrap. Perhaps something like
> > 
> > > 
> > >    #ifndef atomic_cmpxchg_wrap_relaxed
> > >    #define atomic_cmpxchg_wrap_relaxed atomic_cmpxchg_wrap
> > 
> > > 
> > > is missing? I didn't follow the recent changes of that part, so I am
> > > not quite sure...
> > 
> > > 
> > > Thanks!
> > 
> > > 
> > > Colin
> > 
> > > 
> > > In file included from ./include/linux/spinlock.h:406:0,
> >                  from ./include/linux/seqlock.h:35,
> >                  from ./include/linux/time.h:5,
> >                  from ./include/linux/stat.h:18,
> >                  from ./include/linux/module.h:10,
> >                  from net/ipv4/route.c:67:
> > > 
> > > net/ipv4/route.c: In function ‘ip_idents_reserve’:
> > > ./include/linux/atomic.h:459:20: error: implicit declaration of function ‘atomic_cmpxchg_wrap_relaxed’ [-Werror=implicit-function-declaration]
> >   __atomic_op_fence(atomic_cmpxchg_wrap, __VA_ARGS__)
> >                     ^
> > > 
> > > ./include/linux/atomic.h:62:9: note: in definition of macro ‘__atomic_op_fence’
> >  > typeof(op##_relaxed(args)) __ret;    \
> >          ^~
> > > 
> > > net/ipv4/route.c:488:11: note: in expansion of macro ‘atomic_cmpxchg_wrap’
> > >  } while (atomic_cmpxchg_wrap(p_id, old, new) != old);
> > 
> > Oh, I think this is because we don't have atomic_cmpxchg_wrap_relaxed defined neither atomic_xchg_wrap_relaxed. Wonder why this doesn't show up on x86, I did many builds without our x86 changes to verify. 
> > Hans could you please handle this change today to unblock Colin? 
> 
> Could have been this was an error that didn't show up on x86, but not sure why
> cmpxchg and xchg wasn't guarded as the other atomic_*_relaxed functions. This
> whole section is a bit iffy, the aim is to be analogous to the non-wrap relaxed
> functions, but without actually having relaxed_wrap functions, so basically
> these probably always just end up defining the _wrap_relaxed as _wrap functions.
> 
> I've committed a possible "fix". But I cannot confirm since I don't see the
> error on my build setups.
> 

Yep, seems good here! Thanks!

FYI, I use generic config files generated by

    make ARCH=arm defconfig #for v7
    make ARCH=arm imx_v6_v7_defconfig #for generic atomic64 (v6)

Colin