linux-kernel - Re: [RFC PATCH 1/5] bug: Core support for suppressing warning backtraces

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Message-ID: <202403051149.547235C794@keescook>
Date: Tue, 5 Mar 2024 11:54:06 -0800
From: Kees Cook <keescook@...omium.org>
To: Guenter Roeck <linux@...ck-us.net>
Cc: linux-kselftest@...r.kernel.org, David Airlie <airlied@...il.com>,
	Arnd Bergmann <arnd@...db.de>,
	Maíra Canal <mcanal@...lia.com>,
	Dan Carpenter <dan.carpenter@...aro.org>,
	Daniel Diaz <daniel.diaz@...aro.org>,
	David Gow <davidgow@...gle.com>,
	Arthur Grillo <arthurgrillo@...eup.net>,
	Brendan Higgins <brendan.higgins@...ux.dev>,
	Naresh Kamboju <naresh.kamboju@...aro.org>,
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Maxime Ripard <mripard@...nel.org>,
	Ville Syrjälä <ville.syrjala@...ux.intel.com>,
	Daniel Vetter <daniel@...ll.ch>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
	loongarch@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org,
	kunit-dev@...glegroups.com, linux-arch@...r.kernel.org
Subject: Re: [RFC PATCH 1/5] bug: Core support for suppressing warning
 backtraces

On Tue, Mar 05, 2024 at 10:40:29AM -0800, Guenter Roeck wrote:
> [...]
>  	warning = (bug->flags & BUGFLAG_WARNING) != 0;
>  	once = (bug->flags & BUGFLAG_ONCE) != 0;
>  	done = (bug->flags & BUGFLAG_DONE) != 0;
>  
> +	if (warning && IS_SUPPRESSED_WARNING(function))
> +		return BUG_TRAP_TYPE_WARN;
> +

I had to re-read __report_bug() more carefully, but yes, this works --
it's basically leaving early, like "once" does.

This looks like a reasonable approach!

Something very similar to this is checking that a warning happens. i.e.
you talk about drm selftests checking function return values, but I've
got a bunch of tests (LKDTM) that live outside of KUnit because I haven't
had a clean way to check for specific warnings/bugs. I feel like future
changes built on top of this series could add counters or something that
KUnit could examine. E.g. I did this manually for some fortify tests:

https://git.kernel.org/pub/scm/linux/kernel/git/kees/linux.git/commit/?h=for-next/hardening&id=4ce615e798a752d4431fcc52960478906dec2f0e

-Kees

-- 
Kees Cook