linux-kernel - Re: [PATCH 2/9] fortify: Allow KUnit test to build without FORTIFY

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Date:   Thu, 6 Apr 2023 16:09:36 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Daniel Latypov <dlatypov@...gle.com>
Cc:     linux-hardening@...r.kernel.org, Kees Cook <kees@...flux.net>,
        Andy Shevchenko <andy@...nel.org>,
        Cezary Rojewski <cezary.rojewski@...el.com>,
        Puyou Lu <puyou.lu@...il.com>, Mark Brown <broonie@...nel.org>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Brendan Higgins <brendan.higgins@...ux.dev>,
        David Gow <davidgow@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Alexander Potapenko <glider@...gle.com>,
        Zhaoyang Huang <zhaoyang.huang@...soc.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Miguel Ojeda <ojeda@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Liam Howlett <liam.howlett@...cle.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Dan Williams <dan.j.williams@...el.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Yury Norov <yury.norov@...il.com>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        Sander Vanheule <sander@...nheule.net>,
        Eric Biggers <ebiggers@...gle.com>,
        "Masami Hiramatsu (Google)" <mhiramat@...nel.org>,
        Andrey Konovalov <andreyknvl@...il.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        José Expósito <jose.exposito89@...il.com>,
        linux-kernel@...r.kernel.org, kunit-dev@...glegroups.com
Subject: Re: [PATCH 2/9] fortify: Allow KUnit test to build without FORTIFY

On Wed, Apr 05, 2023 at 06:22:25PM -0700, Daniel Latypov wrote:
> On Wed, Apr 5, 2023 at 5:08 PM Kees Cook <keescook@...omium.org> wrote:
> > In order for CI systems to notice all the skipped tests related to
> > CONFIG_FORTIFY_SOURCE, allow the FORTIFY_SOURCE KUnit tests to build
> > with or without CONFIG_FORTIFY_SOURCE.
> 
> Hmm, I wonder if this warrants a deeper discussion.
> It's a lot easier to have tests get disabled by kconfig if their deps
> aren't met.

Yeah, I wasn't sure where to put the "kunit defconfig" settings.
"default.config" didn't seem to actually work as I was expecting. The
real "problem" I'm solving is that FORTIFY_SOURCE isn't in the standard
defconfig.

> If there's pressure to have them compiled and just get marked skipped,
> that sounds like that could be annoying.
> Esp. in the cases where more code needs to be put behind
> 
> #ifdef CONFIG_MY_DEP
> <test helpers, etc>
> #endif
> 
> But I have a suggestion below to simplify this a bit
> 
> >
> > Signed-off-by: Kees Cook <kees@...flux.net>
> > ---
> >  lib/Kconfig.debug   |  2 +-
> >  lib/fortify_kunit.c | 15 +++++++++++++++
> >  2 files changed, 16 insertions(+), 1 deletion(-)
> >
> > diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> > index c8b379e2e9ad..d48a5f4b471e 100644
> > --- a/lib/Kconfig.debug
> > +++ b/lib/Kconfig.debug
> > @@ -2614,7 +2614,7 @@ config STACKINIT_KUNIT_TEST
> >
> >  config FORTIFY_KUNIT_TEST
> >         tristate "Test fortified str*() and mem*() function internals at runtime" if !KUNIT_ALL_TESTS
> > -       depends on KUNIT && FORTIFY_SOURCE
> > +       depends on KUNIT
> >         default KUNIT_ALL_TESTS
> >         help
> >           Builds unit tests for checking internals of FORTIFY_SOURCE as used
> > diff --git a/lib/fortify_kunit.c b/lib/fortify_kunit.c
> > index c8c33cbaae9e..d054fc20a7d5 100644
> > --- a/lib/fortify_kunit.c
> > +++ b/lib/fortify_kunit.c
> > @@ -25,8 +25,21 @@ static const char array_of_10[] = "this is 10";
> >  static const char *ptr_of_11 = "this is 11!";
> >  static char array_unknown[] = "compiler thinks I might change";
> >
> > +/* Handle being built without CONFIG_FORTIFY_SOURCE */
> > +#ifndef __compiletime_strlen
> > +# define __compiletime_strlen __builtin_strlen
> > +#endif
> > +
> > +#define skip_without_fortify() \
> > +do {                           \
> > +       if (!IS_ENABLED(CONFIG_FORTIFY_SOURCE)) \
> > +               kunit_skip(test, "Not built with CONFIG_FORTIFY_SOURCE=y"); \
> > +} while (0)
> 
> Note: you can add an `init` function to the suite and skip the tests there.
> 
> static void fortify_init(struct kunit *test) {
>        if (!IS_ENABLED(CONFIG_FORTIFY_SOURCE))
>                kunit_skip(test, "Not built with CONFIG_FORTIFY_SOURCE=y");
> }
> 
> ...
>   static struct kunit_suite fortify_test_suite = {
>           .name = "fortify",
> +         .init = fortify_init,
>           .test_cases = fortify_test_cases,
>   };
> 
> That way we don't have to add it to each test case.

Ah! Excellent. I didn't realize it would have that effect. I will do
that. :)

-- 
Kees Cook