Date: Tue, 16 Nov 2021 07:37:29 +0100 From: Christophe Leroy <christophe.leroy@...roup.eu> To: Steven Rostedt <rostedt@...dmis.org>, Lukas Bulwahn <lukas.bulwahn@...il.com> Cc: Alexander Popov <alex.popov@...ux.com>, Linus Torvalds <torvalds@...ux-foundation.org>, 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>, 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>, 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>, linux-fsdevel <linux-fsdevel@...r.kernel.org>, notify@...nel.org, main@...ts.elisa.tech, safety-architecture@...ts.elisa.tech, devel@...ts.elisa.tech, Shuah Khan <shuah@...nel.org> Subject: Re: [PATCH v2 0/2] Introduce the pkill_on_warn parameter Le 15/11/2021 à 17:06, Steven Rostedt a écrit : > On Mon, 15 Nov 2021 14:59:57 +0100 > Lukas Bulwahn <lukas.bulwahn@...il.com> wrote: > >> 1. Allow a reasonably configured kernel to boot and run with >> panic_on_warn set. Warnings should only be raised when something is >> not configured as the developers expect it or the kernel is put into a >> state that generally is _unexpected_ and has been exposed little to >> the critical thought of the developer, to testing efforts and use in >> other systems in the wild. Warnings should not be used for something >> informative, which still allows the kernel to continue running in a >> proper way in a generally expected environment. Up to my knowledge, >> there are some kernels in production that run with panic_on_warn; so, >> IMHO, this requirement is generally accepted (we might of course > > To me, WARN*() is the same as BUG*(). If it gets hit, it's a bug in the > kernel and needs to be fixed. I have several WARN*() calls in my code, and > it's all because the algorithms used is expected to prevent the condition > in the warning from happening. If the warning triggers, it means either that > the algorithm is wrong or my assumption about the algorithm is wrong. In > either case, the kernel needs to be updated. All my tests fail if a WARN*() > gets hit (anywhere in the kernel, not just my own). > > After reading all the replies and thinking about this more, I find the > pkill_on_warning actually worse than not doing anything. If you are > concerned about exploits from warnings, the only real solution is a > panic_on_warning. Yes, it brings down the system, but really, it has to be > brought down anyway, because it is in need of a kernel update. > We also have LIVEPATCH to avoid bringing down the system for a kernel update, don't we ? So I wouldn't expect bringing down a vital system just for a WARN. As far as I understand from https://www.kernel.org/doc/html/latest/process/deprecated.html#bug-and-bug-on, WARN() and WARN_ON() are meant to deal with those situations as gracefull as possible, allowing the system to continue running the best it can until a human controled action is taken. So I'd expect the WARN/WARN_ON to be handled and I agree that that pkill_on_warning seems dangerous and unrelevant, probably more dangerous than doing nothing, especially as the WARN may trigger for a reason which has nothing to do with the running thread. Christophe
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