linux-kernel - Re: [PATCH v5] overflow: Introduce overflows_type() and castable_to

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] [day] [month] [year] [list]

Message-ID: <202211021233.02BF0D38@keescook>
Date:   Wed, 2 Nov 2022 12:33:33 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Rasmus Villemoes <rasmus.villemoes@...vas.dk>
Cc:     Gwan-gyeong Mun <gwan-gyeong.mun@...el.com>,
        luc.vanoostenryck@...il.com, nathan@...nel.org,
        ndesaulniers@...gle.com, trix@...hat.com, dlatypov@...gle.com,
        vitor@...saru.org, gustavoars@...nel.org,
        linux-hardening@...r.kernel.org, llvm@...ts.linux.dev,
        jani.nikula@...ux.intel.com, joonas.lahtinen@...ux.intel.com,
        rodrigo.vivi@...el.com, tvrtko.ursulin@...ux.intel.com,
        airlied@...ux.ie, daniel@...ll.ch, linux-kernel@...r.kernel.org,
        intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-sparse@...r.kernel.org, arnd@...nel.org, mchehab@...nel.org,
        mauro.chehab@...ux.intel.com
Subject: Re: [PATCH v5] overflow: Introduce overflows_type() and
 castable_to_type()

On Wed, Nov 02, 2022 at 12:52:32PM +0100, Rasmus Villemoes wrote:
> On 24/10/2022 22.11, Gwan-gyeong Mun wrote:
> > From: Kees Cook <keescook@...omium.org>
> > 
> > Implement a robust overflows_type() macro to test if a variable or
> > constant value would overflow another variable or type. This can be
> > used as a constant expression for static_assert() (which requires a
> > constant expression[1][2]) when used on constant values. This must be
> > constructed manually, since __builtin_add_overflow() does not produce
> > a constant expression[3].
> > 
> > Additionally adds castable_to_type(), similar to __same_type(), but for
> > checking if a constant value would overflow if cast to a given type.
> > 
> 
> > +#define __overflows_type_constexpr(x, T) (			\
> > +	is_unsigned_type(typeof(x)) ?				\
> > +		(x) > type_max(typeof(T)) ? 1 : 0		\
> > +	: is_unsigned_type(typeof(T)) ?				\
> > +		(x) < 0 || (x) > type_max(typeof(T)) ? 1 : 0	\
> > +		: (x) < type_min(typeof(T)) ||			\
> > +		  (x) > type_max(typeof(T)) ? 1 : 0)
> > +
> 
> Can't all these instances of "foo ? 1 : 0" be simplified to "foo"? That
> would improve the readability of this thing somewhat IMO.

Oh, good point. :P I'll fix these.

-- 
Kees Cook