On Thu, Apr 16, 2020 at 12:53:46PM +0100, Will Deacon wrote:
> On Thu, Apr 16, 2020 at 10:31:06AM +0100, Mark Rutland wrote:
> > FWIW, for the arm64 unwind code we could add a helper to snapshot the
> > frame record, and mark that as __no_sanitize_address, e.g.
[...]
> > ... we'd need to do likewied in a few bits of unwind code:
[...]
> Indeed. For now, I'm going to keep this simple with the change below, but
> I'll revisit this later on because I have another series removing
> smp_read_barrier_depends() which makes this a lot simpler.
>
> Will
The below looks good to me; thanks for putting that together!
Mark.
>
> --->8
>
> diff --git a/include/linux/compiler.h b/include/linux/compiler.h
> index 00a68063d9d5..c363d8debc43 100644
> --- a/include/linux/compiler.h
> +++ b/include/linux/compiler.h
> @@ -212,18 +212,12 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
> (typeof(x))__x; \
> })
>
> -/*
> - * Use READ_ONCE_NOCHECK() instead of READ_ONCE() if you need
> - * to hide memory access from KASAN.
> - */
> -#define READ_ONCE_NOCHECK(x) \
> +#define READ_ONCE(x) \
> ({ \
> compiletime_assert_rwonce_type(x); \
> __READ_ONCE_SCALAR(x); \
> })
>
> -#define READ_ONCE(x) READ_ONCE_NOCHECK(x)
> -
> #define __WRITE_ONCE(x, val) \
> do { \
> *(volatile typeof(x) *)&(x) = (val); \
> @@ -247,6 +241,24 @@ do { \
> # define __no_kasan_or_inline __always_inline
> #endif
>
> +static __no_kasan_or_inline
> +unsigned long __read_once_word_nocheck(const void *addr)
> +{
> + return __READ_ONCE(*(unsigned long *)addr);
> +}
> +
> +/*
> + * Use READ_ONCE_NOCHECK() instead of READ_ONCE() if you need to load a
> + * word from memory atomically but without telling KASAN. This is usually
> + * used by unwinding code when walking the stack of a running process.
> + */
> +#define READ_ONCE_NOCHECK(x) \
> +({ \
> + unsigned long __x = __read_once_word_nocheck(&(x)); \
> + smp_read_barrier_depends(); \
> + __x; \
> +})
> +
> static __no_kasan_or_inline
> unsigned long read_word_at_a_time(const void *addr)
> {
