linux-hardening - RE: [PATCH 06/10] fortify: replace __is_constexpr() by is

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Message-ID: <ad4482cc835543578862051431f5174f@AcuMS.aculab.com>
Date: Wed, 4 Dec 2024 18:58:35 +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 06/10] fortify: replace __is_constexpr() by is_const() in
 strlen()

From: Vincent Mailhol
> Sent: 02 December 2024 17:33
> 
> From: Vincent Mailhol <mailhol.vincent@...adoo.fr>
> 
> is_const() is a one to one replacement of __is_constexpr(). Do the
> replacement so that __is_constexpr() can be removed.
> 
> Signed-off-by: Vincent Mailhol <mailhol.vincent@...adoo.fr>
> ---
>  include/linux/fortify-string.h | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/fortify-string.h b/include/linux/fortify-string.h
> index 0d99bf11d260a3482bbe46e35c7553c0ccfb8b94..e3f2f772c5439ef71eb4a904b4ce27956bc69743 100644
> --- a/include/linux/fortify-string.h
> +++ b/include/linux/fortify-string.h
> @@ -254,8 +254,8 @@ __FORTIFY_INLINE __kernel_size_t strnlen(const char * const POS p, __kernel_size
>   * Returns number of characters in @p (NOT including the final NUL).
>   *
>   */
> -#define strlen(p)							\
> -	__builtin_choose_expr(__is_constexpr(__builtin_strlen(p)),	\
> +#define strlen(p)						\
> +	__builtin_choose_expr(is_const(__builtin_strlen(p)),	\
>  		__builtin_strlen(p), __fortify_strlen(p))

I'm sure Linus suggested a way of doing that without replicating
the __builtin_strlen().

Indeed it may be valid to do:
	len = __builtin_strlen(p);
	__builtin_constant_p(len) ? len : __fortify_strlen(p);

	David

>  __FORTIFY_INLINE __diagnose_as(__builtin_strlen, 1)
>  __kernel_size_t __fortify_strlen(const char * const POS p)
> 
> --
> 2.45.2
> 
> 

-
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