From: Thomas Gleixner <tglx@linutronix.de>
To: Dmitry Vyukov <dvyukov@google.com>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
Ingo Molnar <mingo@redhat.com>,
Mark Rutland <mark.rutland@arm.com>,
Peter Zijlstra <peterz@infradead.org>,
Will Deacon <will.deacon@arm.com>,
"H. Peter Anvin" <hpa@zytor.com>,
Andrey Ryabinin <aryabinin@virtuozzo.com>,
kasan-dev <kasan-dev@googlegroups.com>,
"x86@kernel.org" <x86@kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH] locking/atomics: don't alias ____ptr
Date: Wed, 28 Jun 2017 13:10:14 +0200 (CEST) [thread overview]
Message-ID: <alpine.DEB.2.20.1706281306120.1970@nanos> (raw)
In-Reply-To: <CACT4Y+Yhy-jucOC37um5xZewEj0sdw8Hjte7oOYxDdxkzOTYoA@mail.gmail.com>
On Wed, 28 Jun 2017, Dmitry Vyukov wrote:
> On Wed, Jun 28, 2017 at 12:02 PM, Sebastian Andrzej Siewior <bigeasy@linutronix.de> wrote:
> > @@ -359,16 +359,16 @@ static __always_inline bool atomic64_add_negative(s64 i, atomic64_t *v)
> >
> > #define cmpxchg64(ptr, old, new) \
> > ({ \
> > - __typeof__(ptr) ____ptr = (ptr); \
> > - kasan_check_write(____ptr, sizeof(*____ptr)); \
> > - arch_cmpxchg64(____ptr, (old), (new)); \
> > + __typeof__(ptr) ____ptr64 = (ptr); \
> > + kasan_check_write(____ptr64, sizeof(*____ptr64));\
> > + arch_cmpxchg64(____ptr64, (old), (new)); \
> > })
> >
> > #define cmpxchg64_local(ptr, old, new) \
> > ({ \
> > - __typeof__(ptr) ____ptr = (ptr); \
> > - kasan_check_write(____ptr, sizeof(*____ptr)); \
> > - arch_cmpxchg64_local(____ptr, (old), (new)); \
> > + __typeof__(ptr) ____ptr64 = (ptr); \
> > + kasan_check_write(____ptr64, sizeof(*____ptr64));\
> > + arch_cmpxchg64_local(____ptr64, (old), (new)); \
> > })
> >
> > #define cmpxchg_double(p1, p2, o1, o2, n1, n2) \
>
>
> Doh! Thanks for fixing this. I think I've a similar crash in a
> different place when I developed the patch.
> The problem is that when we do:
>
> __typeof__(ptr) ____ptr = (ptr); \
> arch_cmpxchg64_local(____ptr, (old), (new)); \
>
> We don't necessary pass value of our just declared ____ptr to
> arch_cmpxchg64_local(). We just pass a symbolic identifier. So if
> arch_cmpxchg64_local() declares own ____ptr and then tries to use what
> we passed ("____ptr") it will actually refer to own variable declared
> rather than to what we wanted to pass in.
>
> In my case I ended up with something like:
>
> __typeof__(foo) __ptr = __ptr;
>
> which compiler decided to turn into 0.
>
> Thank you, macros.
>
> We can add more underscores, but the problem can happen again. Should
> we prefix current function/macro name to all local vars?..
Actually we can void that ___ptr dance completely.
Thanks,
tglx
8<--------------------
--- a/include/asm-generic/atomic-instrumented.h
+++ b/include/asm-generic/atomic-instrumented.h
@@ -359,37 +359,32 @@ static __always_inline bool atomic64_add
#define cmpxchg(ptr, old, new) \
({ \
- __typeof__(ptr) ___ptr = (ptr); \
- kasan_check_write(___ptr, sizeof(*___ptr)); \
+ kasan_check_write((ptr), sizeof(*(ptr))); \
arch_cmpxchg((ptr), (old), (new)); \
})
#define sync_cmpxchg(ptr, old, new) \
({ \
- __typeof__(ptr) ___ptr = (ptr); \
- kasan_check_write(___ptr, sizeof(*___ptr)); \
- arch_sync_cmpxchg(___ptr, (old), (new)); \
+ kasan_check_write((ptr), sizeof(*(ptr))); \
+ arch_sync_cmpxchg((ptr), (old), (new)); \
})
#define cmpxchg_local(ptr, old, new) \
({ \
- __typeof__(ptr) ____ptr = (ptr); \
- kasan_check_write(____ptr, sizeof(*____ptr)); \
- arch_cmpxchg_local(____ptr, (old), (new)); \
+ kasan_check_write((ptr), sizeof(*(ptr))); \
+ arch_cmpxchg_local((ptr), (old), (new)); \
})
#define cmpxchg64(ptr, old, new) \
({ \
- __typeof__(ptr) ____ptr = (ptr); \
- kasan_check_write(____ptr, sizeof(*____ptr)); \
- arch_cmpxchg64(____ptr, (old), (new)); \
+ kasan_check_write((ptr), sizeof(*(ptr))); \
+ arch_cmpxchg64((ptr), (old), (new)); \
})
#define cmpxchg64_local(ptr, old, new) \
({ \
- __typeof__(ptr) ____ptr = (ptr); \
- kasan_check_write(____ptr, sizeof(*____ptr)); \
- arch_cmpxchg64_local(____ptr, (old), (new)); \
+ kasan_check_write((ptr), sizeof(*(ptr))); \
+ arch_cmpxchg64_local((ptr), (old), (new)); \
})
/*
next prev parent reply other threads:[~2017-06-28 11:10 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-06-22 14:14 [PATCH v5 0/4] x86, kasan: add KASAN checks to atomic operations Dmitry Vyukov
[not found] ` <cover.1498140838.git.dvyukov@google.com>
2017-06-22 14:14 ` [PATCH v5 1/4] x86: switch atomic.h to use atomic-instrumented.h Dmitry Vyukov
2017-06-22 21:14 ` Andrew Morton
2017-06-23 8:23 ` Dmitry Vyukov
2017-06-23 8:54 ` Ingo Molnar
2017-06-23 19:00 ` Andrew Morton
2017-06-23 13:59 ` [tip:locking/core] locking/atomic/x86: Switch " tip-bot for Dmitry Vyukov
2017-06-22 14:14 ` [PATCH v5 2/4] kasan: allow kasan_check_read/write() to accept pointers to volatiles Dmitry Vyukov
2017-06-23 14:00 ` [tip:locking/core] kasan: Allow " tip-bot for Dmitry Vyukov
2017-07-26 12:10 ` tip-bot for Dmitry Vyukov
2017-06-22 14:14 ` [PATCH v5 3/4] asm-generic: add KASAN instrumentation to atomic operations Dmitry Vyukov
2017-06-23 14:01 ` [tip:locking/core] locking/atomics, asm-generic: Add " tip-bot for Dmitry Vyukov
2017-06-28 10:02 ` [PATCH] locking/atomics: don't alias ____ptr Sebastian Andrzej Siewior
2017-06-28 10:16 ` Dmitry Vyukov
2017-06-28 11:10 ` Thomas Gleixner [this message]
2017-06-28 11:12 ` Dmitry Vyukov
2017-06-28 11:21 ` Thomas Gleixner
2017-06-28 12:45 ` Mark Rutland
2017-06-28 12:24 ` Thomas Gleixner
2017-06-28 12:27 ` Dmitry Vyukov
2017-06-28 13:33 ` Thomas Gleixner
2017-06-28 11:15 ` Andrey Ryabinin
2017-06-28 12:12 ` Sebastian Andrzej Siewior
2017-06-28 13:20 ` Thomas Gleixner
2017-06-28 13:54 ` Thomas Gleixner
2017-06-28 14:14 ` Mark Rutland
2017-06-28 15:24 ` Thomas Gleixner
2017-06-28 15:54 ` Mark Rutland
2017-06-28 16:56 ` Ingo Molnar
2017-06-28 18:21 ` Thomas Gleixner
2017-06-29 6:47 ` Thomas Gleixner
2017-06-28 14:00 ` Andrey Ryabinin
2017-06-22 14:14 ` [PATCH v5 4/4] asm-generic, x86: add comments for atomic instrumentation Dmitry Vyukov
2017-06-23 14:01 ` [tip:locking/core] locking/atomic/x86, asm-generic: Add " tip-bot for Dmitry Vyukov
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