On Wed, 28 Jun 2017, Dmitry Vyukov wrote:
> On Wed, Jun 28, 2017 at 12:02 PM, Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> 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)); \
})
/*
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