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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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