linux-kernel - Re: [PATCH] ubsan: Tighten UBSAN

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Date:   Fri, 3 Mar 2023 12:29:23 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Nathan Chancellor <nathan@...nel.org>
Cc:     Marco Elver <elver@...gle.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nicolas Schier <nicolas@...sle.eu>, Tom Rix <trix@...hat.com>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Miroslav Benes <mbenes@...e.cz>, linux-kbuild@...r.kernel.org,
        llvm@...ts.linux.dev,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] ubsan: Tighten UBSAN_BOUNDS on GCC

On Fri, Mar 03, 2023 at 08:44:33AM -0700, Nathan Chancellor wrote:
> On Thu, Mar 02, 2023 at 02:54:45PM -0800, Kees Cook wrote:
> > [...]
> >  config CC_HAS_UBSAN_ARRAY_BOUNDS
> >  	def_bool $(cc-option,-fsanitize=array-bounds)
> > +	help
> > +	  The -fsanitize=array-bounds option is only available on Clang,
> > +	  and is actually composed of two more specific options,
> > +	  -fsanitize=array-bounds and -fsanitize=local-bounds. However,
> > +	  -fsanitize=local-bounds can only be used when trap mode is
> > +	  enabled. (See also the help for CONFIG_LOCAL_BOUNDS.)
> 
> The first sentence does not read right to me, you have array-bounds
> twice. I think the first one wants to be just bounds?

Oops, yes. I rewrote that a few times and seem to have gotten lost. I
think it is better written as:

	  Under Clang, the -fsanitize=bounds option is actually composed
	  of two more specific options, -fsanitize=array-bounds and
	  -fsanitize=local-bounds. However, -fsanitize=local-bounds can
	  only be used when trap mode is enabled. (See also the help for
	  CONFIG_LOCAL_BOUNDS.) Explicitly check for -fsanitize=array-bounds
	  so that we can build up the options needed for UBSAN_BOUNDS
	  with or without UBSAN_TRAP.


-- 
Kees Cook