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Date: Mon, 25 Jun 2018 13:38:03 +0200
From: Andrea Parri <andrea.parri@...rulasolutions.com>
To: Mark Rutland <mark.rutland@....com>
Cc: linux-kernel@...r.kernel.org, will.deacon@....com,
peterz@...radead.org, boqun.feng@...il.com,
Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [PATCHv2 03/11] atomics: simplify cmpxchg() instrumentation
On Mon, Jun 25, 2018 at 11:59:44AM +0100, Mark Rutland wrote:
> Currently we define some fairly verbose wrappers for the cmpxchg()
> family so that we can pass a pointer and size into kasan_check_write().
>
> The wrapper duplicate the size-switching logic necessary in arch code,
> and only work for scalar types. On some architectures, (cmp)xchg are
> used on non-scalar types, and thus the instrumented wrappers need to be
> able to handle this.
>
> We could take the type-punning logic form {READ,WRITE}_ONCE(), but this
> makes the wrappers even more verbose, and requires several local
> variables in the macros.
>
> Instead, let's simplify the wrappers into simple macros which:
>
> * snapshot the pointer into a single local variable, called __ai_ptr to
> avoid conflicts with variables in the scope of the caller.
>
> * call kasan_check_read() on __ai_ptr.
Maybe I'm misreading the diff: aren't you calling kasan_check_write()?
(not sure if it makes a difference in this case/for KTSan, but CMPXCHG
does not necessarily perform a write...)
Andrea
>
> * invoke the arch_ function, passing the original arguments, bar
> __ai_ptr being substituted for ptr.
>
> There should be no functional change as a result of this patch.
>
> Signed-off-by: Mark Rutland <mark.rutland@....com>
> Cc: Boqun Feng <boqun.feng@...il.com>
> Cc: Dmitry Vyukov <dvyukov@...gle.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Will Deacon <will.deacon@....com>
> ---
> include/asm-generic/atomic-instrumented.h | 100 +++++-------------------------
> 1 file changed, 15 insertions(+), 85 deletions(-)
>
> diff --git a/include/asm-generic/atomic-instrumented.h b/include/asm-generic/atomic-instrumented.h
> index 3c64e95d5ed0..c7c3e4cdd942 100644
> --- a/include/asm-generic/atomic-instrumented.h
> +++ b/include/asm-generic/atomic-instrumented.h
> @@ -408,109 +408,39 @@ static __always_inline bool atomic64_add_negative(s64 i, atomic64_t *v)
> }
> #endif
>
> -static __always_inline unsigned long
> -cmpxchg_size(volatile void *ptr, unsigned long old, unsigned long new, int size)
> -{
> - kasan_check_write(ptr, size);
> - switch (size) {
> - case 1:
> - return arch_cmpxchg((u8 *)ptr, (u8)old, (u8)new);
> - case 2:
> - return arch_cmpxchg((u16 *)ptr, (u16)old, (u16)new);
> - case 4:
> - return arch_cmpxchg((u32 *)ptr, (u32)old, (u32)new);
> - case 8:
> - BUILD_BUG_ON(sizeof(unsigned long) != 8);
> - return arch_cmpxchg((u64 *)ptr, (u64)old, (u64)new);
> - }
> - BUILD_BUG();
> - return 0;
> -}
> -
> #define cmpxchg(ptr, old, new) \
> ({ \
> - ((__typeof__(*(ptr)))cmpxchg_size((ptr), (unsigned long)(old), \
> - (unsigned long)(new), sizeof(*(ptr)))); \
> + typeof(ptr) __ai_ptr = (ptr); \
> + kasan_check_write(__ai_ptr, sizeof(*__ai_ptr)); \
> + arch_cmpxchg(__ai_ptr, (old), (new)); \
> })
>
> -static __always_inline unsigned long
> -sync_cmpxchg_size(volatile void *ptr, unsigned long old, unsigned long new,
> - int size)
> -{
> - kasan_check_write(ptr, size);
> - switch (size) {
> - case 1:
> - return arch_sync_cmpxchg((u8 *)ptr, (u8)old, (u8)new);
> - case 2:
> - return arch_sync_cmpxchg((u16 *)ptr, (u16)old, (u16)new);
> - case 4:
> - return arch_sync_cmpxchg((u32 *)ptr, (u32)old, (u32)new);
> - case 8:
> - BUILD_BUG_ON(sizeof(unsigned long) != 8);
> - return arch_sync_cmpxchg((u64 *)ptr, (u64)old, (u64)new);
> - }
> - BUILD_BUG();
> - return 0;
> -}
> -
> #define sync_cmpxchg(ptr, old, new) \
> ({ \
> - ((__typeof__(*(ptr)))sync_cmpxchg_size((ptr), \
> - (unsigned long)(old), (unsigned long)(new), \
> - sizeof(*(ptr)))); \
> + typeof(ptr) __ai_ptr = (ptr); \
> + kasan_check_write(__ai_ptr, sizeof(*__ai_ptr)); \
> + arch_sync_cmpxchg(__ai_ptr, (old), (new)); \
> })
>
> -static __always_inline unsigned long
> -cmpxchg_local_size(volatile void *ptr, unsigned long old, unsigned long new,
> - int size)
> -{
> - kasan_check_write(ptr, size);
> - switch (size) {
> - case 1:
> - return arch_cmpxchg_local((u8 *)ptr, (u8)old, (u8)new);
> - case 2:
> - return arch_cmpxchg_local((u16 *)ptr, (u16)old, (u16)new);
> - case 4:
> - return arch_cmpxchg_local((u32 *)ptr, (u32)old, (u32)new);
> - case 8:
> - BUILD_BUG_ON(sizeof(unsigned long) != 8);
> - return arch_cmpxchg_local((u64 *)ptr, (u64)old, (u64)new);
> - }
> - BUILD_BUG();
> - return 0;
> -}
> -
> #define cmpxchg_local(ptr, old, new) \
> ({ \
> - ((__typeof__(*(ptr)))cmpxchg_local_size((ptr), \
> - (unsigned long)(old), (unsigned long)(new), \
> - sizeof(*(ptr)))); \
> + typeof(ptr) __ai_ptr = (ptr); \
> + kasan_check_write(__ai_ptr, sizeof(*__ai_ptr)); \
> + arch_cmpxchg_local(__ai_ptr, (old), (new)); \
> })
>
> -static __always_inline u64
> -cmpxchg64_size(volatile u64 *ptr, u64 old, u64 new)
> -{
> - kasan_check_write(ptr, sizeof(*ptr));
> - return arch_cmpxchg64(ptr, old, new);
> -}
> -
> #define cmpxchg64(ptr, old, new) \
> ({ \
> - ((__typeof__(*(ptr)))cmpxchg64_size((ptr), (u64)(old), \
> - (u64)(new))); \
> + typeof(ptr) __ai_ptr = (ptr); \
> + kasan_check_write(__ai_ptr, sizeof(*__ai_ptr)); \
> + arch_cmpxchg64(__ai_ptr, (old), (new)); \
> })
>
> -static __always_inline u64
> -cmpxchg64_local_size(volatile u64 *ptr, u64 old, u64 new)
> -{
> - kasan_check_write(ptr, sizeof(*ptr));
> - return arch_cmpxchg64_local(ptr, old, new);
> -}
> -
> #define cmpxchg64_local(ptr, old, new) \
> ({ \
> - ((__typeof__(*(ptr)))cmpxchg64_local_size((ptr), (u64)(old), \
> - (u64)(new))); \
> + typeof(ptr) __ai_ptr = (ptr); \
> + kasan_check_write(__ai_ptr, sizeof(*__ai_ptr)); \
> + arch_cmpxchg64_local(__ai_ptr, (old), (new)); \
> })
>
> /*
> --
> 2.11.0
>
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