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Message-ID: <1fa12030-ba88-e6e8-6aca-4aedac790cc1@ispras.ru> Date: Wed, 27 Jul 2022 19:43:01 +0300 From: Alexey Khoroshilov <khoroshilov@...ras.ru> To: Jann Horn <jannh@...gle.com> Cc: Linus Torvalds <torvalds@...ux-foundation.org>, Petr Mladek <pmladek@...e.com>, "Paul E. McKenney" <paulmck@...nel.org>, Alexander Popov <alex.popov@...ux.com>, Jonathan Corbet <corbet@....net>, 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>, 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>, Christophe Leroy <christophe.leroy@...roup.eu>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Mark Rutland <mark.rutland@....com>, Andy Lutomirski <luto@...nel.org>, Dave Hansen <dave.hansen@...ux.intel.com>, Steven Rostedt <rostedt@...dmis.org>, Thomas Garnier <thgarnie@...gle.com>, Will Deacon <will.deacon@....com>, Ard Biesheuvel <ard.biesheuvel@...aro.org>, Laura Abbott <labbott@...hat.com>, David S Miller <davem@...emloft.net>, Borislav Petkov <bp@...en8.de>, Kernel Hardening <kernel-hardening@...ts.openwall.com>, linux-hardening@...r.kernel.org, "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, notify@...nel.org Subject: Re: [PATCH] Introduce the pkill_on_warn boot parameter On 27.07.2022 19:30, Jann Horn wrote: > On Wed, Jul 27, 2022 at 6:17 PM Alexey Khoroshilov > <khoroshilov@...ras.ru> wrote: >> On 01.10.2021 22:59, Linus Torvalds wrote: >> Coming back to the discussion of WARN_ON()/pr_warn("WARNING:") semantics. >> >> We see a number of cases where WARNING is used to inform userspace that >> it is doing something wrong, e.g. >> https://elixir.bootlin.com/linux/v5.19-rc8/source/net/can/j1939/socket.c#L181 >> https://elixir.bootlin.com/linux/v5.19-rc8/source/drivers/video/fbdev/core/fbmem.c#L1023 >> >> It is definitely useful, but it does not make sense in case of fuzzing >> when the userspace should do wrong things and check if kernel behaves >> correctly. >> >> As a result we have warnings with two different intentions: >> - warn that something wrong happens in kernel, but we are able to continue; >> - warn userspace that it is doing something wrong. >> >> During fuzzing we would like to report the former and to ignore the >> latter. Are any ideas how these intentions can be recognized automatically? > > https://elixir.bootlin.com/linux/v5.19-rc8/source/include/asm-generic/bug.h#L74 > says: > > * WARN(), WARN_ON(), WARN_ON_ONCE, and so on can be used to report > * significant kernel issues that need prompt attention if they should ever > * appear at runtime. > * > * Do not use these macros when checking for invalid external inputs > * (e.g. invalid system call arguments, or invalid data coming from > * network/devices), and on transient conditions like ENOMEM or EAGAIN. > * These macros should be used for recoverable kernel issues only. > * For invalid external inputs, transient conditions, etc use > * pr_err[_once/_ratelimited]() followed by dump_stack(), if necessary. > * Do not include "BUG"/"WARNING" in format strings manually to make these > * conditions distinguishable from kernel issues. > > So if you see drivers intentionally using WARN() or printing > "WARNING:" on codepaths that are reachable with bogus inputs from > userspace, those codepaths should be fixed to log warnings in a > different format. Thank you, Jann! I have missed that. -- Alexey
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