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Date: Sat, 13 Nov 2021 21:14:39 +0300
From: Alexander Popov <alex.popov@...ux.com>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Jonathan Corbet <corbet@....net>, Paul McKenney <paulmck@...nel.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Thomas Gleixner <tglx@...utronix.de>, Peter Zijlstra <peterz@...radead.org>,
Joerg Roedel <jroedel@...e.de>, Maciej Rozycki <macro@...am.me.uk>,
Muchun Song <songmuchun@...edance.com>,
Viresh Kumar <viresh.kumar@...aro.org>, Robin Murphy <robin.murphy@....com>,
Randy Dunlap <rdunlap@...radead.org>, Lu Baolu <baolu.lu@...ux.intel.com>,
Petr Mladek <pmladek@...e.com>, Kees Cook <keescook@...omium.org>,
Luis Chamberlain <mcgrof@...nel.org>, Wei Liu <wl@....org>,
John Ogness <john.ogness@...utronix.de>,
Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
Alexey Kardashevskiy <aik@...abs.ru>,
Christophe Leroy <christophe.leroy@...roup.eu>, Jann Horn
<jannh@...gle.com>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Mark Rutland <mark.rutland@....com>, Andy Lutomirski <luto@...nel.org>,
Dave Hansen <dave.hansen@...ux.intel.com>,
Steven Rostedt <rostedt@...dmis.org>, Will Deacon <will@...nel.org>,
Ard Biesheuvel <ardb@...nel.org>, Laura Abbott <labbott@...nel.org>,
David S Miller <davem@...emloft.net>, Borislav Petkov <bp@...en8.de>,
Arnd Bergmann <arnd@...db.de>, Andrew Scull <ascull@...gle.com>,
Marc Zyngier <maz@...nel.org>, Jessica Yu <jeyu@...nel.org>,
Iurii Zaikin <yzaikin@...gle.com>,
Rasmus Villemoes <linux@...musvillemoes.dk>, Wang Qing <wangqing@...o.com>,
Mel Gorman <mgorman@...e.de>,
Mauro Carvalho Chehab <mchehab+huawei@...nel.org>,
Andrew Klychkov <andrew.a.klychkov@...il.com>,
Mathieu Chouquet-Stringer <me@...hieu.digital>,
Daniel Borkmann <daniel@...earbox.net>, Stephen Kitt <steve@....org>,
Stephen Boyd <sboyd@...nel.org>,
Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
Mike Rapoport <rppt@...nel.org>, Bjorn Andersson
<bjorn.andersson@...aro.org>,
Kernel Hardening <kernel-hardening@...ts.openwall.com>,
linux-hardening@...r.kernel.org,
"open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
linux-arch <linux-arch@...r.kernel.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
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main@...ts.elisa.tech, safety-architecture@...ts.elisa.tech,
devel@...ts.elisa.tech, Shuah Khan <shuah@...nel.org>,
Lukas Bulwahn <lukas.bulwahn@...il.com>
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 <alex.popov@...ux.com> 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,
Alexander
[1]: https://en.wikipedia.org/wiki/Fail-fast
[2]: https://a13xp0p0v.github.io/2020/02/15/CVE-2019-18683.html
[3]: https://www.usenix.org/system/files/sec22summer_zou.pdf
[4]: http://lkml.iu.edu/hypermail/linux/kernel/1610.0/01217.html
[5]: https://elisa.tech/
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