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From:   Arnd Bergmann <arnd@arndb.de>
Date:   Wed, 15 Jan 2020 20:54:59 +0100
Message-ID: <CAK8P3a3WywSsahH2vtZ_EOYTWE44YdN+Pj6G8nt_zrL3sckdwQ@mail.gmail.com>
Subject: Re: [PATCH -rcu] asm-generic, kcsan: Add KCSAN instrumentation for bitops
To:     Marco Elver <elver@google.com>
Cc:     "Paul E. McKenney" <paulmck@kernel.org>,
        Andrey Konovalov <andreyknvl@google.com>,
        Alexander Potapenko <glider@google.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        kasan-dev <kasan-dev@googlegroups.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        christophe leroy <christophe.leroy@c-s.fr>,
        Daniel Axtens <dja@axtens.net>,
        linux-arch <linux-arch@vger.kernel.org>
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On Wed, Jan 15, 2020 at 8:51 PM Marco Elver <elver@google.com> wrote:
>
> On Wed, 15 Jan 2020 at 20:27, Arnd Bergmann <arnd@arndb.de> wrote:
> >
> > On Wed, Jan 15, 2020 at 5:58 PM Marco Elver <elver@google.com> wrote:
> > >   * set_bit - Atomically set a bit in memory
> > > @@ -26,6 +27,7 @@
> > >  static inline void set_bit(long nr, volatile unsigned long *addr)
> > >  {
> > >         kasan_check_write(addr + BIT_WORD(nr), sizeof(long));
> > > +       kcsan_check_atomic_write(addr + BIT_WORD(nr), sizeof(long));
> > >         arch_set_bit(nr, addr);
> > >  }
> >
> > It looks like you add a kcsan_check_atomic_write or kcsan_check_write directly
> > next to almost any instance of kasan_check_write().
> >
> > Are there any cases where we actually just need one of the two but not the
> > other? If not, maybe it's better to rename the macro and have it do both things
> > as needed?
>
> Do you mean adding an inline helper at the top of each bitops header
> here, similar to what we did for atomic-instrumented?  Happy to do
> that if it improves readability.

I was thinking of treewide wrappers, given that there are only a couple of files
calling kasan_check_write():

$ git grep -wl kasan_check_write
arch/arm64/include/asm/barrier.h
arch/arm64/include/asm/uaccess.h
arch/x86/include/asm/uaccess_64.h
include/asm-generic/atomic-instrumented.h
include/asm-generic/bitops/instrumented-atomic.h
include/asm-generic/bitops/instrumented-lock.h
include/asm-generic/bitops/instrumented-non-atomic.h
include/linux/kasan-checks.h
include/linux/uaccess.h
lib/iov_iter.c
lib/strncpy_from_user.c
lib/usercopy.c
scripts/atomic/gen-atomic-instrumented.sh

Are there any that really just want kasan_check_write() but not one
of the kcsan checks?

      Arnd