From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 304B3C433EF for ; Wed, 29 Sep 2021 19:02:00 +0000 (UTC) Received: from mother.openwall.net (mother.openwall.net [195.42.179.200]) by mail.kernel.org (Postfix) with SMTP id 29C8E613A6 for ; Wed, 29 Sep 2021 19:01:58 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 29C8E613A6 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linux.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=lists.openwall.com Received: (qmail 25664 invoked by uid 550); 29 Sep 2021 19:01:51 -0000 Mailing-List: contact kernel-hardening-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Received: (qmail 25640 invoked from network); 29 Sep 2021 19:01:50 -0000 X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:reply-to:subject:to:cc:references:from :message-id:date:user-agent:mime-version:in-reply-to :content-language:content-transfer-encoding; bh=mEoo1pQnu6pHp5PWM8SXaa1FHr3gfkl9owRi01q3hsE=; b=HiYqmbJHLxezMGmNkS4k6T/1hKRowAIHMVJOPuWa03CRWpql/OCzW98vsSu86YX+q1 tdAIpWBh0cfaev9Pg4V532Dh7F8N6ew6OwWt8bkkS7kLroxziiPWLSs/wtgsLf7HTFrO hWRG+XKHh1DnzOXB1tHre1pHeS/9UD0oqXFkCzLhF7ZtJsAaKThtYcDUgs/bGhymObWj 0I5l3eF6CW2pw7AUfWc4oLfOjlG35NxmRWmVpxFRv5lni9wfF49XlZNjqtaQgk9Sjl4Q 9FFl8QmuvI/S6FDjXlMyiW+L2K7Nzh7t+Xzhi6bOUBppyoewZa6IR30i2GPrWfedp0+b JNaQ== X-Gm-Message-State: AOAM532B4i3vcPxdG6Ipk6UqGaL3tl6nEu/MfoQOqYJ4/sSXq/hXYkGL 0Eo9/Qbgd+oHdK3m9Cd2uLs= X-Google-Smtp-Source: ABdhPJy1ardq98oFiY34LpGEOjDmhtsZmRBhn3UkbjGJZMFFKb47vUt0fbZWbD1yt5tsb4oHfHeY7Q== X-Received: by 2002:a05:6000:1546:: with SMTP id 6mr1776663wry.305.1632942098923; Wed, 29 Sep 2021 12:01:38 -0700 (PDT) Subject: Re: [PATCH] Introduce the pkill_on_warn boot parameter To: 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 , Thomas Garnier , Will Deacon , Ard Biesheuvel , Laura Abbott , David S Miller , Borislav Petkov , kernel-hardening@lists.openwall.com, linux-hardening@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org Cc: notify@kernel.org References: <20210929185823.499268-1-alex.popov@linux.com> From: Alexander Popov Message-ID: Date: Wed, 29 Sep 2021 22:01:33 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <20210929185823.499268-1-alex.popov@linux.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit 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 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. Best regards, Alexander > --- > Documentation/admin-guide/kernel-parameters.txt | 4 ++++ > kernel/panic.c | 5 +++++ > 2 files changed, 9 insertions(+) > > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt > index 91ba391f9b32..86c748907666 100644 > --- a/Documentation/admin-guide/kernel-parameters.txt > +++ b/Documentation/admin-guide/kernel-parameters.txt > @@ -4112,6 +4112,10 @@ > pirq= [SMP,APIC] Manual mp-table setup > See Documentation/x86/i386/IO-APIC.rst. > > + pkill_on_warn= Kill all threads in a process that provoked a > + kernel warning. > + Format: { "0" | "1" } > + > plip= [PPT,NET] Parallel port network link > Format: { parport | timid | 0 } > See also Documentation/admin-guide/parport.rst. > diff --git a/kernel/panic.c b/kernel/panic.c > index cefd7d82366f..47b728bfb1d3 100644 > --- a/kernel/panic.c > +++ b/kernel/panic.c > @@ -53,6 +53,7 @@ static int pause_on_oops_flag; > static DEFINE_SPINLOCK(pause_on_oops_lock); > bool crash_kexec_post_notifiers; > int panic_on_warn __read_mostly; > +int pkill_on_warn __read_mostly; > unsigned long panic_on_taint; > bool panic_on_taint_nousertaint = false; > > @@ -610,6 +611,9 @@ void __warn(const char *file, int line, void *caller, unsigned taint, > > print_oops_end_marker(); > > + if (pkill_on_warn && system_state >= SYSTEM_RUNNING) > + do_group_exit(SIGKILL); > + > /* Just a warning, don't kill lockdep. */ > add_taint(taint, LOCKDEP_STILL_OK); > } > @@ -694,6 +698,7 @@ core_param(panic, panic_timeout, int, 0644); > core_param(panic_print, panic_print, ulong, 0644); > core_param(pause_on_oops, pause_on_oops, int, 0644); > core_param(panic_on_warn, panic_on_warn, int, 0644); > +core_param(pkill_on_warn, pkill_on_warn, int, 0644); > core_param(crash_kexec_post_notifiers, crash_kexec_post_notifiers, bool, 0644); > > static int __init oops_setup(char *s) >