From: Alexander Popov <alex.popov@linux.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Jonathan Corbet <corbet@lwn.net>,
Paul McKenney <paulmck@kernel.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>,
Petr Mladek <pmladek@suse.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>,
Jann Horn <jannh@google.com>,
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>,
Will Deacon <will.deacon@arm.com>,
David S Miller <davem@davemloft.net>,
Borislav Petkov <bp@alien8.de>,
kernel-hardening@lists.openwall.com,
linux-hardening@vger.kernel.org, linux-doc@vger.kernel.org,
linux-kernel@vger.kernel.org, notify@kernel.org
Subject: Re: [PATCH] Introduce the pkill_on_warn boot parameter
Date: Thu, 30 Sep 2021 21:27:43 +0300 [thread overview]
Message-ID: <de96ffec-bbd8-2724-9285-0867cd9a08a0@linux.com> (raw)
In-Reply-To: <20210929163143.aa8b70ac9d5cf0b628823370@linux-foundation.org>
On 30.09.2021 02:31, Andrew Morton wrote:
> On Wed, 29 Sep 2021 22:01:33 +0300 Alexander Popov <alex.popov@linux.com> wrote:
>
>> On 29.09.2021 21:58, Alexander Popov 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, so attackers use kernel
>>> warning infoleak in vulnerability exploits. See the examples:
>>> https://a13xp0p0v.github.io/2020/02/15/CVE-2019-18683.html
>>> https://a13xp0p0v.github.io/2021/02/09/CVE-2021-26708.html
>>>
>>> Let's introduce the pkill_on_warn boot 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.
>>>
>>> Signed-off-by: Alexander Popov <alex.popov@linux.com>
>>
>> This patch was tested using CONFIG_LKDTM.
>> The kernel kills a process that performs this:
>> echo WARNING > /sys/kernel/debug/provoke-crash/DIRECT
>>
>> If you are fine with this approach, I will prepare a patch adding the
>> pkill_on_warn sysctl.
>
> Why do we need a boot parameter? Isn't a sysctl all we need for this
> feature?
I would say we need both sysctl and boot parameter for pkill_on_warn.
That would be consistent with panic_on_warn, ftrace_dump_on_oops and
oops/panic_on_oops.
> Also,
>
> if (pkill_on_warn && system_state >= SYSTEM_RUNNING)
> do_group_exit(SIGKILL);
>
> - why do we care about system_state? An explanatory code comment
> seems appropriate.
>
> - do we really want to do this in states > SYSTEM_RUNNING? If so, why?
A kernel warning may occur at any moment.
I don't have a deep understanding of possible side effects on early boot stages.
So I decided that at least it's safer to avoid interfering before SYSTEM_RUNNING.
Best regards,
Alexander
next prev parent reply other threads:[~2021-09-30 18:27 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-29 18:58 [PATCH] Introduce the pkill_on_warn boot parameter Alexander Popov
2021-09-29 19:01 ` Alexander Popov
2021-09-29 19:49 ` Paul E. McKenney
2021-09-30 9:15 ` Petr Mladek
2021-09-30 15:05 ` Alexander Popov
2021-10-01 12:23 ` Petr Mladek
2021-09-30 16:59 ` Steven Rostedt
2021-10-01 12:09 ` Petr Mladek
2021-09-30 18:28 ` Kees Cook
2021-10-01 19:59 ` Linus Torvalds
2021-10-02 11:41 ` Alexander Popov
2021-10-02 12:13 ` Steven Rostedt
2021-10-02 16:33 ` Alexander Popov
2021-10-02 16:52 ` Linus Torvalds
2021-10-02 21:05 ` Alexander Popov
2021-10-05 19:48 ` Eric W. Biederman
2021-10-06 14:56 ` Alexander Popov
2021-10-22 17:30 ` Alexander Popov
2022-07-27 16:17 ` Alexey Khoroshilov
2022-07-27 16:30 ` Jann Horn
2022-07-27 16:43 ` Alexey Khoroshilov
2022-07-27 16:42 ` Linus Torvalds
2022-07-27 17:47 ` Alexey Khoroshilov
2021-09-29 23:31 ` Andrew Morton
2021-09-30 18:27 ` Alexander Popov [this message]
2021-09-30 18:36 ` Kees Cook
2021-09-29 19:03 ` Dave Hansen
2021-09-29 19:47 ` Peter Zijlstra
2021-09-29 20:06 ` Kees Cook
2021-09-30 13:55 ` Alexander Popov
2021-09-30 18:20 ` Kees Cook
2021-10-02 18:04 ` Al Viro
2021-10-02 18:31 ` Steven Rostedt
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