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 CA99CC433F5 for ; Sat, 2 Oct 2021 21:06:22 +0000 (UTC) Received: from mother.openwall.net (mother.openwall.net [195.42.179.200]) by mail.kernel.org (Postfix) with SMTP id D660361B24 for ; Sat, 2 Oct 2021 21:06:21 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org D660361B24 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 1419 invoked by uid 550); 2 Oct 2021 21:06:13 -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 1384 invoked from network); 2 Oct 2021 21:06:12 -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=5H/GFVPqJxpNuzq9DTTrJ9nYbSkD2Uo4JrRe91cjYbs=; b=wmr0j8DpR/WVrjFqlDDCr9aR+g1z/1QXinYdpF627k3d8qC+fPCe9O9e/oUIiAZGDZ JN3qBV7mB/ss0ZimvNC9mMjaVu7ta7yeIji6YjjKENfiuTpn+cYhwj+a/+R6ijQuvG2o JrQbmpVhu54D4yJFKe56+2VDlUlxsk2lF6RqYegvYAOJOys6bsxgeVNt+ukNWTNN9TBu 7VD1ZaPUvj1J4Q8X2xqg8dwG+XgC4qkx94HeTkeAa/AFpoMLDAo3DIyPEccJDTyAwZho szZaFdBUPC9JzvCYyiS/mtwgeR4BeGLKCjHCfhelr5XkpTItg6BWA6CaVEPqAn8M6gHI VVXw== X-Gm-Message-State: AOAM530KP63cnv7VGGFedIIJQCLeWdKnLwyFdblLEz0en0rYgcumr98o S4NGYs5jPliwuC0epnyG97M= X-Google-Smtp-Source: ABdhPJwYfEVPx9sGnNGcKfk+RdHjOSBlPv7Nzvdneo7e6BX2JSVXpOIrqI0GJQjGi7+1lZHBuoznpw== X-Received: by 2002:adf:e30d:: with SMTP id b13mr5072345wrj.438.1633208761027; Sat, 02 Oct 2021 14:06:01 -0700 (PDT) Subject: Re: [PATCH] Introduce the pkill_on_warn boot parameter To: Linus Torvalds Cc: Petr Mladek , "Paul E. McKenney" , Jonathan Corbet , Andrew Morton , Thomas Gleixner , Peter Zijlstra , Joerg Roedel , Maciej Rozycki , Muchun Song , Viresh Kumar , Robin Murphy , Randy Dunlap , Lu Baolu , 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 , David S Miller , Borislav Petkov , Kernel Hardening , linux-hardening@vger.kernel.org, "open list:DOCUMENTATION" , Linux Kernel Mailing List , notify@kernel.org References: <20210929185823.499268-1-alex.popov@linux.com> <20210929194924.GA880162@paulmck-ThinkPad-P17-Gen-1> From: Alexander Popov Message-ID: <0e847d7f-7bf0-cdd4-ba6e-a742ce877a38@linux.com> Date: Sun, 3 Oct 2021 00:05:56 +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: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit On 02.10.2021 19:52, Linus Torvalds wrote: > On Sat, Oct 2, 2021 at 4:41 AM Alexander Popov wrote: >> >> And what do you think about the proposed pkill_on_warn? > > Honestly, I don't see the point. > > If you can reliably trigger the WARN_ON some way, you can probably > cause more problems by fooling some other process to trigger it. > > And if it's unintentional, then what does the signal help? > > So rather than a "rationale" that makes little sense, I'd like to hear > of an actual _use_ case. That's different. That's somebody actually > _using_ that pkill to good effect for some particular load. I was thinking about a use case for you and got an insight. Bugs usually don't come alone. Killing the process that got WARN_ON() prevents possible bad effects **after** the warning. For example, in my exploit for CVE-2019-18683, the kernel warning happens **before** the memory corruption (use-after-free in the V4L2 subsystem). https://a13xp0p0v.github.io/2020/02/15/CVE-2019-18683.html So pkill_on_warn allows the kernel to stop the process when the first signs of wrong behavior are detected. In other words, proceeding with the code execution from the wrong state can bring more disasters later. > That said, I don't much care in the end. But it sounds like a > pointless option to just introduce yet another behavior to something > that should never happen anyway, and where the actual > honest-to-goodness reason for WARN_ON() existing is already being > fulfilled (ie syzbot has been very effective at flushing things like > that out). Yes, we slowly get rid of kernel warnings. However, the syzbot dashboard still shows a lot of them. Even my small syzkaller setup finds plenty of new warnings. I believe fixing all of them will take some time. And during that time, pkill_on_warn may be a better reaction to WARN_ON() than ignoring and proceeding with the execution. Is that reasonable? Best regards, Alexander