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Message-ID: <20161102065505.GA381@linaro.org>
Date: Wed, 2 Nov 2016 15:55:08 +0900
From: AKASHI Takahiro <takahiro.akashi@...aro.org>
To: kernel-hardening@...ts.openwall.com
Cc: Colin Vidal <colin@...dal.org>,
"keescook@...omium.org" <keescook@...omium.org>,
"arnd@...db.de" <arnd@...db.de>,
"tglx@...utronix.de" <tglx@...utronix.de>,
"mingo@...hat.com" <mingo@...hat.com>,
"Anvin, H Peter" <h.peter.anvin@...el.com>,
Hans Liljestrand <ishkamiel@...il.com>,
David Windsor <dwindsor@...il.com>
Subject: Re: [RFC v3 PATCH 01/13] Add architecture
independent hardened atomic base
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?
>
> Actually this brings us to the fact that we tried to stay away from various relaxed/acquire/release functions (in providing default wrap implementations), but it seems that they are also needed...
This is just a reminder.
There is a potential inconsistency in naming:
atomic_xx_wrap_relaxed vs. atomic_xx_relaxed_wrap
See:
http://www.openwall.com/lists/kernel-hardening/2016/10/25/7
-Takahiro AKASHI
> Sigh.. This grows bigger and bigger every day. I hope atomic doesn't plan to come with more functions in the nearest future :)
>
> Kees, what is your opinion on relaxed/acquire/release coverage?
>
> Best Regards,
> Elena.
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