Re: [PATCH 1/3] kcov: remove #ifdef CONFIG_RANDOMIZE_BASE

Mark Rutland
2017-09-19T13:32:23Z

Hi,

On Tue, Sep 19, 2017 at 03:46:46PM +0300, Andrey Ryabinin wrote:
> There is no need to surround kaslr_offset() with CONFIG_RANDOMIZE_BASE ifdef.
> kaslr_offset() will just return 0 if CONFIG_RANDOMIZE_BASE isn't set.
>
> Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
> ---
> kernel/kcov.c | 2 --
> 1 file changed, 2 deletions(-)
>
> diff --git a/kernel/kcov.c b/kernel/kcov.c
> index 3f693a0f6f3e..2f0e7a7c7afc 100644
> --- a/kernel/kcov.c
> +++ b/kernel/kcov.c
> @@ -69,9 +69,7 @@ void notrace __sanitizer_cov_trace_pc(void)
> unsigned long pos;
> unsigned long ip = _RET_IP_;
>
> -#ifdef CONFIG_RANDOMIZE_BASE
> ip -= kaslr_offset();
> -#endif

I think this is sound, but as Dmitry points out it'll mean we do some
pointless work. For example on arm64 we have:

static inline unsigned long kaslr_offset(void)
{
return kimage_vaddr - KIMAGE_VADDR;
}

... where kimage_vaddr is a global variable, and KIMAGE_VADDR is a
constant (and should be identical for !CONFIG_RANDOMIZE_BASE kernels).

I think it would be reasonable to make that:

static inline unsigned long kaslr_offset(void)
{
if (!IS_ENABLED(CONFIG_RANDOMIZE_BASE))
return 0;

return kimage_vaddr - KIMAGE_VADDR;
}

... and simplify callers as above.

Thanks,
Mark.