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Date: Sat, 2 Oct 2021 08:13:59 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Alexander Popov <alex.popov@...ux.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>, Petr Mladek
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Kernel Hardening <kernel-hardening@...ts.openwall.com>,
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<linux-doc@...r.kernel.org>, Linux Kernel Mailing List
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Subject: Re: [PATCH] Introduce the pkill_on_warn boot parameter
On Sat, 2 Oct 2021 14:41:34 +0300
Alexander Popov <alex.popov@...ux.com> wrote:
> Currently, the Linux kernel provides two types of reaction to kernel warnings:
> 1. Do nothing (by default),
> 2. Call panic() if panic_on_warn is set. That's a very strong reaction,
> so panic_on_warn is usually disabled on production systems.
>
> >From a safety point of view, the Linux kernel misses a middle way of handling
> kernel warnings:
> - The kernel should stop the activity that provokes a warning,
> - But the kernel should avoid complete denial of service.
>
> >From a security point of view, kernel warning messages provide a lot of useful
> information for attackers. Many GNU/Linux distributions allow unprivileged users
> to read the kernel log (for various reasons), so attackers use kernel warning
> infoleak in vulnerability exploits. See the examples:
> https://a13xp0p0v.github.io/2021/02/09/CVE-2021-26708.html
> https://a13xp0p0v.github.io/2020/02/15/CVE-2019-18683.html
> https://googleprojectzero.blogspot.com/2018/09/a-cache-invalidation-bug-in-linux.html
>
> Let's introduce the pkill_on_warn parameter.
> If this parameter is set, the kernel kills all threads in a process that
> provoked a kernel warning. This behavior is reasonable from a safety point of
> view described above. It is also useful for kernel security hardening because
> the system kills an exploit process that hits a kernel warning.
How does this help? It only kills the process that caused the warning,
it doesn't kill the process that spawned it. This is trivial to get
around. Just fork a process, trigger the warning (it gets killed) and
then read the kernel log.
If this is your rationale, then I'm not convinced this helps at all.
-- Steve
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