linux-hardening - RE: [PATCH 04/10] linux/bits.h: simplify GENMASK_INPUT_CHECK() by using is_const

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <dff4cdd543104e3792e4856375f310c1@AcuMS.aculab.com>
Date: Wed, 4 Dec 2024 18:52:10 +0000
From: David Laight <David.Laight@...LAB.COM>
To: Vincent Mailhol <mailhol.vincent@...adoo.fr>, Linus Torvalds
	<torvalds@...ux-foundation.org>, Luc Van Oostenryck
	<luc.vanoostenryck@...il.com>, Nathan Chancellor <nathan@...nel.org>, "Nick
 Desaulniers" <ndesaulniers@...gle.com>, Bill Wendling <morbo@...gle.com>,
	Justin Stitt <justinstitt@...gle.com>, Yury Norov <yury.norov@...il.com>,
	Rasmus Villemoes <linux@...musvillemoes.dk>, Kees Cook <kees@...nel.org>,
	"Gustavo A. R. Silva" <gustavoars@...nel.org>, Jani Nikula
	<jani.nikula@...ux.intel.com>, Joonas Lahtinen
	<joonas.lahtinen@...ux.intel.com>, Rodrigo Vivi <rodrigo.vivi@...el.com>,
	Tvrtko Ursulin <tursulin@...ulin.net>, David Airlie <airlied@...il.com>,
	Simona Vetter <simona@...ll.ch>, Suzuki K Poulose <suzuki.poulose@....com>,
	Mike Leach <mike.leach@...aro.org>, James Clark <james.clark@...aro.org>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Rikard Falkeborn
	<rikard.falkeborn@...il.com>, Martin Uecker
	<Martin.Uecker@....uni-goettingen.de>
CC: "linux-sparse@...r.kernel.org" <linux-sparse@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"llvm@...ts.linux.dev" <llvm@...ts.linux.dev>,
	"linux-hardening@...r.kernel.org" <linux-hardening@...r.kernel.org>,
	"intel-gfx@...ts.freedesktop.org" <intel-gfx@...ts.freedesktop.org>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	"coresight@...ts.linaro.org" <coresight@...ts.linaro.org>,
	"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>
Subject: RE: [PATCH 04/10] linux/bits.h: simplify GENMASK_INPUT_CHECK() by
 using is_const_true()

From: Vincent Mailhol
> Sent: 02 December 2024 17:33
> 
>   __builtin_choose_expr(__is_constexpr((l) > (h)), (l) > (h), 0)
> 
> is equivalent to:
> 
>   is_const_true((l) > (h))

Change it to BUILD_BUG_ON_MSG(statically_true((l) < (h)), "error message")

and then fix all the fallout :-)

	David

> 
> Apply is_const_true() to simplify GENMASK_INPUT_CHECK().
> 
> Signed-off-by: Vincent Mailhol <mailhol.vincent@...adoo.fr>
> ---
> This change passes the unit tests from CONFIG_BITS_TEST, including the
> extra negative tests provided under #ifdef TEST_GENMASK_FAILURES [1].
> 
> [1] commit 6d511020e13d ("lib/test_bits.c: add tests of GENMASK")
> Link: https://git.kernel.org/torvalds/c/6d511020e13d
> ---
>  include/linux/bits.h | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/bits.h b/include/linux/bits.h
> index 60044b6088172b3f26aa3f17cdaede9786863dae..ef0119e6179e1ca95345a3d4d3327ba19633028e 100644
> --- a/include/linux/bits.h
> +++ b/include/linux/bits.h
> @@ -20,9 +20,8 @@
>   */
>  #if !defined(__ASSEMBLY__)
>  #include <linux/build_bug.h>
> -#define GENMASK_INPUT_CHECK(h, l) \
> -	(BUILD_BUG_ON_ZERO(__builtin_choose_expr( \
> -		__is_constexpr((l) > (h)), (l) > (h), 0)))
> +#include <linux/compiler.h>
> +#define GENMASK_INPUT_CHECK(h, l) BUILD_BUG_ON_ZERO(is_const_true((l) > (h)))
>  #else
>  /*
>   * BUILD_BUG_ON_ZERO is not available in h files included from asm files,
> 
> --
> 2.45.2
> 

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)