linux-hardening - Re: [PATCH v2] overflow: Introduce overflows_type() and castable_to

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Date:   Mon, 26 Sep 2022 13:17:18 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Gwan-gyeong Mun <gwan-gyeong.mun@...el.com>,
        Luc Van Oostenryck <luc.vanoostenryck@...il.com>,
        Nathan Chancellor <nathan@...nel.org>,
        Tom Rix <trix@...hat.com>,
        Daniel Latypov <dlatypov@...gle.com>,
        Vitor Massaru Iha <vitor@...saru.org>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        linux-hardening@...r.kernel.org, llvm@...ts.linux.dev,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>, linux-kernel@...r.kernel.org,
        intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-sparse@...r.kernel.org, Arnd Bergmann <arnd@...nel.org>
Subject: Re: [PATCH v2] overflow: Introduce overflows_type() and castable_to_type()

+ Arnd

On Mon, Sep 26, 2022 at 12:11 PM Kees Cook <keescook@...omium.org> wrote:
> ---
> v2:
>  - fix comment typo
>  - wrap clang pragma to avoid GCC warnings
>  - style nit cleanups
>  - rename __castable_to_type() to castable_to_type()
>  - remove prior overflows_type() definition
> v1: https://lore.kernel.org/lkml/20220926003743.409911-1-keescook@chromium.org
> diff --git a/lib/overflow_kunit.c b/lib/overflow_kunit.c
> index f385ca652b74..fffc3f86181d 100644
> --- a/lib/overflow_kunit.c
> +++ b/lib/overflow_kunit.c
> @@ -16,6 +16,11 @@
>  #include <linux/types.h>
>  #include <linux/vmalloc.h>
>
> +/* We're expecting to do a lot of "always true" or "always false" tests. */
> +#ifdef CONFIG_CC_IS_CLANG
> +#pragma clang diagnostic ignored "-Wtautological-constant-out-of-range-compare"
> +#endif

Any chance we can reuse parts of __diag_ignore or __diag_clang from
include/linux/compiler_types.h or include/linux/compiler-clang.h
respectively?

Those are needed for pragmas within preprocessor macros, which we
don't have here, but I suspect they may be more concise to use here.

> +#define TEST_SAME_TYPE(t1, t2, same)                   do {    \
> +       typeof(t1) __t1h = type_max(t1);                        \
> +       typeof(t1) __t1l = type_min(t1);                        \
> +       typeof(t2) __t2h = type_max(t2);                        \
> +       typeof(t2) __t2l = type_min(t2);                        \

Can we use __auto_type here rather than typeof(macro expansion)?
-- 
Thanks,
~Nick Desaulniers