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Date:   Sat, 13 Nov 2021 21:14:39 +0300
From:   Alexander Popov <>
To:     Linus Torvalds <>
Cc:     Jonathan Corbet <>,
        Paul McKenney <>,
        Andrew Morton <>,
        Thomas Gleixner <>,
        Peter Zijlstra <>,
        Joerg Roedel <>,
        Maciej Rozycki <>,
        Muchun Song <>,
        Viresh Kumar <>,
        Robin Murphy <>,
        Randy Dunlap <>,
        Lu Baolu <>,
        Petr Mladek <>,
        Kees Cook <>,
        Luis Chamberlain <>, Wei Liu <>,
        John Ogness <>,
        Andy Shevchenko <>,
        Alexey Kardashevskiy <>,
        Christophe Leroy <>,
        Jann Horn <>,
        Greg Kroah-Hartman <>,
        Mark Rutland <>,
        Andy Lutomirski <>,
        Dave Hansen <>,
        Steven Rostedt <>,
        Will Deacon <>,
        Ard Biesheuvel <>,
        Laura Abbott <>,
        David S Miller <>,
        Borislav Petkov <>, Arnd Bergmann <>,
        Andrew Scull <>,
        Marc Zyngier <>, Jessica Yu <>,
        Iurii Zaikin <>,
        Rasmus Villemoes <>,
        Wang Qing <>, Mel Gorman <>,
        Mauro Carvalho Chehab <>,
        Andrew Klychkov <>,
        Mathieu Chouquet-Stringer <>,
        Daniel Borkmann <>,
        Stephen Kitt <>, Stephen Boyd <>,
        Thomas Bogendoerfer <>,
        Mike Rapoport <>,
        Bjorn Andersson <>,
        Kernel Hardening <>,,
        "open list:DOCUMENTATION" <>,
        linux-arch <>,
        Linux Kernel Mailing List <>,
        linux-fsdevel <>,,,,, Shuah Khan <>,
        Lukas Bulwahn <>
Subject: Re: [PATCH v2 0/2] Introduce the pkill_on_warn parameter

On 13.11.2021 00:26, Linus Torvalds wrote:
> On Fri, Nov 12, 2021 at 10:52 AM Alexander Popov <> wrote:
>> Hello everyone!
>> Friendly ping for your feedback.
> I still haven't heard a compelling _reason_ for this all, and why
> anybody should ever use this or care?

Ok, to sum up:

Killing the process that hit a kernel warning complies with the Fail-Fast 
principle [1]. pkill_on_warn sysctl allows the kernel to stop the process when 
the **first signs** of wrong behavior are detected.

By default, the Linux kernel ignores a warning and proceeds the execution from 
the flawed state. That is opposite to the Fail-Fast principle.
A kernel warning may be followed by memory corruption or other negative effects, 
like in CVE-2019-18683 exploit [2] or many other cases detected by the SyzScope 
project [3]. pkill_on_warn would prevent the system from the errors going after 
a warning in the process context.

At the same time, pkill_on_warn does not kill the entire system like 
panic_on_warn. That is the middle way of handling kernel warnings.
Linus, it's similar to your BUG_ON() policy [4]. The process hitting BUG_ON() is 
killed, and the system proceeds to work. pkill_on_warn just brings a similar 
policy to WARN_ON() handling.

I believe that many Linux distros (which don't hit WARN_ON() here and there) 
will enable pkill_on_warn because it's reasonable from the safety and security 
points of view.

And I'm sure that the ELISA project by the Linux Foundation (Enabling Linux In 
Safety Applications [5]) would support the pkill_on_warn sysctl.
[Adding people from this project to CC]

I hope that I managed to show the rationale.

Best regards,


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