Re: [kernel-hardening] atomic64_wrap_t generic implementation

[AKASHI Takahiro <takahiro.akashi@linaro.org>]

On Wed, Oct 12, 2016 at 09:42:12PM +0200, Colin Vidal wrote:
> Hi Elena,
> 
> diff --git a/include/asm-generic/atomic64.h b/include/asm-generic/atomic64.h
> index dad68bf..4987419 100644
> --- a/include/asm-generic/atomic64.h
> +++ b/include/asm-generic/atomic64.h
> @@ -16,6 +16,8 @@ typedef struct {
>         long long counter;
>  } atomic64_t;
>  
> +typedef atomic64_t atomic64_wrap_t;
> +
>  #define ATOMIC64_INIT(i)       { (i) }
>  
>  extern long long atomic64_read(const atomic64_t *v);
> @@ -62,4 +64,15 @@ extern int    atomic64_add_unless(atomic64_t *v, long long a, long long u);
>  #define atomic64_dec_and_test(v)       (atomic64_dec_return((v)) == 0)
>  #define atomic64_inc_not_zero(v)       atomic64_add_unless((v), 1LL, 0LL)
>  
> +#define atomic64_read_wrap(v) atomic64_read(v)
> +#define atomic64_set_wrap(v, i) atomic64_set((v), (i))
> +#define atomic64_add_wrap(a, v) atomic64_add((a), (v))
> +#define atomic64_add_return_wrap(a, v) atomic64_add_return((a), (v))
> +#define atomic64_sub_wrap(a, v) atomic64_sub((a), (v))
> +#define atomic64_inc_wrap(v) atomic64_inc(v)
> +#define atomic64_inc_return_wrap(v) atomic64_inc_return(v)
> +#define atomic64_dec_wrap(v) atomic64_dec(v)
> +#define atomic64_cmpxchg_wrap(v, o, n) atomic64_cmpxchg((v), (o), (n))
> +#define atomic64_xchg_wrap(v, n) atomic64_xchg((v), (n))
> 
> Isen't there a type error ? For instance:
> 
> atomic64_wrap_t atom_wrap;
> 
> atomic64_read_wrap(atom_wrap) will be expanded into
> atomic64_read(atom_wrap), which would lead to a type error (atomic64_t
> expected).
> 
> Perhaps the more simple thing to do would be
> 
> -typedef atomic64_t atomic64_wrap_t;

As atomic64_wrap_t is always defined in include/linux/types.h
(under CONFIG_64BIT), this definition should not be here.

> +#define atomic64_wrap_t atomic64_t

and it would be better off to always define atomic(64)_wrap_t as a struct
in order to detect potential misusages like:
    atomic64_t atom_var;
    atomic64_read_wrap(&atom_var);
?

Thanks,
-Takahiro AKASHI

> since the implementations are the same here.
> 
> Or I missed something obvious?
> 
> Thanks,
> 
> Colin