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Subject: Re: [PATCH] Introduce the pkill_on_warn boot parameter
To:     Jann Horn <jannh@google.com>
Cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        Petr Mladek <pmladek@suse.com>,
        "Paul E. McKenney" <paulmck@kernel.org>,
        Alexander Popov <alex.popov@linux.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Andrew Morton <akpm@linux-foundation.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Peter Zijlstra <peterz@infradead.org>,
        Joerg Roedel <jroedel@suse.de>,
        Maciej Rozycki <macro@orcam.me.uk>,
        Muchun Song <songmuchun@bytedance.com>,
        Viresh Kumar <viresh.kumar@linaro.org>,
        Robin Murphy <robin.murphy@arm.com>,
        Randy Dunlap <rdunlap@infradead.org>,
        Lu Baolu <baolu.lu@linux.intel.com>,
        Kees Cook <keescook@chromium.org>,
        Luis Chamberlain <mcgrof@kernel.org>, Wei Liu <wl@xen.org>,
        John Ogness <john.ogness@linutronix.de>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Alexey Kardashevskiy <aik@ozlabs.ru>,
        Christophe Leroy <christophe.leroy@csgroup.eu>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Andy Lutomirski <luto@kernel.org>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Thomas Garnier <thgarnie@google.com>,
        Will Deacon <will.deacon@arm.com>,
        Ard Biesheuvel <ard.biesheuvel@linaro.org>,
        Laura Abbott <labbott@redhat.com>,
        David S Miller <davem@davemloft.net>,
        Borislav Petkov <bp@alien8.de>,
        Kernel Hardening <kernel-hardening@lists.openwall.com>,
        linux-hardening@vger.kernel.org,
        "open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        notify@kernel.org
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From:   Alexey Khoroshilov <khoroshilov@ispras.ru>
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Message-ID: <1fa12030-ba88-e6e8-6aca-4aedac790cc1@ispras.ru>
Date:   Wed, 27 Jul 2022 19:43:01 +0300
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On 27.07.2022 19:30, Jann Horn wrote:
> On Wed, Jul 27, 2022 at 6:17 PM Alexey Khoroshilov
> <khoroshilov@ispras.ru> wrote:
>> On 01.10.2021 22:59, Linus Torvalds wrote:
>> Coming back to the discussion of WARN_ON()/pr_warn("WARNING:") semantics.
>>
>> We see a number of cases where WARNING is used to inform userspace that
>> it is doing something wrong, e.g.
>> https://elixir.bootlin.com/linux/v5.19-rc8/source/net/can/j1939/socket.c#L181
>> https://elixir.bootlin.com/linux/v5.19-rc8/source/drivers/video/fbdev/core/fbmem.c#L1023
>>
>> It is definitely useful, but it does not make sense in case of fuzzing
>> when the userspace should do wrong things and check if kernel behaves
>> correctly.
>>
>> As a result we have warnings with two different intentions:
>> - warn that something wrong happens in kernel, but we are able to continue;
>> - warn userspace that it is doing something wrong.
>>
>> During fuzzing we would like to report the former and to ignore the
>> latter. Are any ideas how these intentions can be recognized automatically?
> 
> https://elixir.bootlin.com/linux/v5.19-rc8/source/include/asm-generic/bug.h#L74
> says:
> 
>  * WARN(), WARN_ON(), WARN_ON_ONCE, and so on can be used to report
>  * significant kernel issues that need prompt attention if they should ever
>  * appear at runtime.
>  *
>  * Do not use these macros when checking for invalid external inputs
>  * (e.g. invalid system call arguments, or invalid data coming from
>  * network/devices), and on transient conditions like ENOMEM or EAGAIN.
>  * These macros should be used for recoverable kernel issues only.
>  * For invalid external inputs, transient conditions, etc use
>  * pr_err[_once/_ratelimited]() followed by dump_stack(), if necessary.
>  * Do not include "BUG"/"WARNING" in format strings manually to make these
>  * conditions distinguishable from kernel issues.
> 
> So if you see drivers intentionally using WARN() or printing
> "WARNING:" on codepaths that are reachable with bogus inputs from
> userspace, those codepaths should be fixed to log warnings in a
> different format.

Thank you, Jann!

I have missed that.

--
Alexey