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From:   Alexander Potapenko <glider@google.com>
Date:   Tue, 11 Dec 2018 23:25:28 +0100
Message-ID: <CAG_fn=U2d799W6GiujK4pedkLZr=LJrFrZhfCQ=Kin35quA76g@mail.gmail.com>
Subject: Re: [PATCH] kasan: fix kasan_check_read/write definitions
To:     Dmitriy Vyukov <dvyukov@google.com>
Cc:     Arnd Bergmann <arnd@arndb.de>,
        Andrew Morton <akpm@linux-foundation.org>,
        Andrey Ryabinin <aryabinin@virtuozzo.com>,
        anders.roxell@linaro.org,
        Ard Biesheuvel <ard.biesheuvel@linaro.org>,
        Will Deacon <will.deacon@arm.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Andrey Konovalov <andreyknvl@google.com>,
        Stephen Rothwell <sfr@canb.auug.org.au>,
        kasan-dev <kasan-dev@googlegroups.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Linux Memory Management List <linux-mm@kvack.org>
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On Tue, Dec 11, 2018 at 2:45 PM Dmitry Vyukov <dvyukov@google.com> wrote:
>
> On Tue, Dec 11, 2018 at 2:35 PM Arnd Bergmann <arnd@arndb.de> wrote:
> >
> > Building little-endian allmodconfig kernels on arm64 started failing
> > with the generated atomic.h implementation, since we now try to call
> > kasan helpers from the EFI stub:
> >
> > aarch64-linux-gnu-ld: drivers/firmware/efi/libstub/arm-stub.stub.o: in =
function `atomic_set':
> > include/generated/atomic-instrumented.h:44: undefined reference to `__e=
fistub_kasan_check_write'
> >
> > I suspect that we get similar problems in other files that explicitly
> > disable KASAN for some reason but call atomic_t based helper functions.
> >
> > We can fix this by checking the predefined __SANITIZE_ADDRESS__ macro
> > that the compiler sets instead of checking CONFIG_KASAN, but this in tu=
rn
> > requires a small hack in mm/kasan/common.c so we do see the extern
> > declaration there instead of the inline function.
>
>
> Alexander, I think you are doing a similar thing for similar reasons
> in KMSAN patch (see KMSAN_CHECK_ATOMIC_PARAMS):
> https://github.com/google/kmsan/commit/17ebbfe19624c84adf79b0e5a74fd258c4=
9ff12b
> Namely, non-KMSAN-instrumented files must not get KMSAN callbacks from
> atomics too.
I'll need to double-check, but it occurs to me that we won't need
additional hooks for atomics in KMSAN - the compiler instrumentation
should suffice.

> Arnd patch does it the other way around: non-instrumented files need
> to opt-in instead of opt-out.
Shouldn't we put __SANITIZE_ADDRESS__ somewhere into mm/kasan/kasan.h then?
> Let's settle on a common way to do this, so that we can use it
> consistently across all tools.
>
>
>
> > Fixes: b1864b828644 ("locking/atomics: build atomic headers as required=
")
> > Reported-by: Anders Roxell <anders.roxell@linaro.org>
> > Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> > ---
> >  include/linux/kasan-checks.h | 2 +-
> >  mm/kasan/common.c            | 2 ++
> >  2 files changed, 3 insertions(+), 1 deletion(-)
> >
> > diff --git a/include/linux/kasan-checks.h b/include/linux/kasan-checks.=
h
> > index d314150658a4..a61dc075e2ce 100644
> > --- a/include/linux/kasan-checks.h
> > +++ b/include/linux/kasan-checks.h
> > @@ -2,7 +2,7 @@
> >  #ifndef _LINUX_KASAN_CHECKS_H
> >  #define _LINUX_KASAN_CHECKS_H
> >
> > -#ifdef CONFIG_KASAN
> > +#if defined(__SANITIZE_ADDRESS__) || defined(__KASAN_INTERNAL)
> >  void kasan_check_read(const volatile void *p, unsigned int size);
> >  void kasan_check_write(const volatile void *p, unsigned int size);
> >  #else
> > diff --git a/mm/kasan/common.c b/mm/kasan/common.c
> > index 03d5d1374ca7..51a7932c33a3 100644
> > --- a/mm/kasan/common.c
> > +++ b/mm/kasan/common.c
> > @@ -14,6 +14,8 @@
> >   *
> >   */
> >
> > +#define __KASAN_INTERNAL
> > +
> >  #include <linux/export.h>
> >  #include <linux/interrupt.h>
> >  #include <linux/init.h>
> > --
> > 2.20.0
> >


--=20
Alexander Potapenko
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