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

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Message-ID: <CAMZ6RqLsiOF=5FZ=U2MtZ01iBYKZHtfZ5Zi4t3m=L5Oc4EPHGg@mail.gmail.com>
Date: Fri, 6 Dec 2024 00:49:43 +0900
From: Vincent Mailhol <mailhol.vincent@...adoo.fr>
To: David Laight <David.Laight@...lab.com>
Cc: 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>, 
	"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()

On Thu. 5 Dec 2024 at 03:52, David Laight <David.Laight@...lab.com> wrote:
> 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 :-)

BUILD_BUG_ON_MSG() is not suitable for GENMASK_INPUT_CHECK. We need
one of the variants that returns zero here.

But I agree that it is good to have a more meaningful error message
here. I will use __BUILD_BUG_ON_ZERO_MSG() in v2.


Yours sincerely,
Vincent Mailhol