Re: [PATCH v3 05/12] arm64: csum: Disable KASAN for do_csum()

[Mark Rutland <mark.rutland@arm.com>]

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)
>  {