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Date: Tue, 5 Mar 2024 12:17:55 -0800
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Subject: Re: [RFC PATCH 1/5] bug: Core support for suppressing warning
 backtraces
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To: Kees Cook <keescook@chromium.org>
Cc: linux-kselftest@vger.kernel.org, David Airlie <airlied@gmail.com>,
 Arnd Bergmann <arnd@arndb.de>, =?UTF-8?Q?Ma=C3=ADra_Canal?=
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 <202403051149.547235C794@keescook>
From: Guenter Roeck <linux@roeck-us.net>
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In-Reply-To: <202403051149.547235C794@keescook>
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On 3/5/24 11:54, Kees Cook wrote:
> 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
> 

Sounds like a good idea. It should be straightforward to add a counter
to struct __suppressed_warning. This way the calling code could easily
check if an expected warning backtrace actually happened.

Thanks,
Guenter