[PATCH v6 13/14] aarch64: redefine RETURN_ADDRESS to strip PAC

[Adhemerval Zanella]

On 01/07/2020 11:40, Szabolcs Nagy wrote:
> RETURN_ADDRESS is used at several places in glibc to mean a valid
> code address of the call site, but with pac-ret it may contain a
> pointer authentication code (PAC), so its definition is adjusted.
> 
> This is gcc PR target/94891: __builtin_return_address should not
> expose signed pointers to user code where it can cause ABI issues.
> In glibc RETURN_ADDRESS is only changed if it is built with pac-ret.
> There is no detection for the specific gcc issue because it is
> hard to test and the additional xpac does not cause problems.

LGTM, thanks.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

> ---
>  sysdeps/aarch64/sysdep.h | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/sysdeps/aarch64/sysdep.h b/sysdeps/aarch64/sysdep.h
> index 2879aeaa5c..48fa8e9e90 100644
> --- a/sysdeps/aarch64/sysdep.h
> +++ b/sysdeps/aarch64/sysdep.h
> @@ -44,6 +44,13 @@ strip_pac (void *p)
>    asm ("hint 7 // xpaclri" : "+r"(ra));
>    return ra;
>  }
> +
> +/* This is needed when glibc is built with -mbranch-protection=pac-ret
> +   with a gcc that is affected by PR target/94891.  */
> +# if HAVE_AARCH64_PAC_RET
> +#  undef RETURN_ADDRESS
> +#  define RETURN_ADDRESS(n) strip_pac (__builtin_return_address (n))
> +# endif
>  #endif
>  
>  #ifdef	__ASSEMBLER__
> 

Ok.