Re: [PATCH] Introduce the pkill_on_warn boot parameter

From: Kees Cook <keescook@chromium.org>
To: Dave Hansen <dave.hansen@intel.com>
Cc: Alexander Popov <alex.popov@linux.com>,
	Jonathan Corbet <corbet@lwn.net>,
	Paul McKenney <paulmck@kernel.org>,
	Andrew Morton <akpm@linux-foundation.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>,
	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>,
	Thomas Garnier <thgarnie@google.com>,
	Will Deacon <will.deacon@arm.com>,
	Ard Biesheuvel <ard.biesheuvel@linaro.org>,
	Laura Abbott <labbott@redhat.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: Wed, 29 Sep 2021 13:06:59 -0700	[thread overview]
Message-ID: <202109291229.C64A1D9D@keescook> (raw)
In-Reply-To: <323d0784-249d-7fef-6c60-e8426d35b083@intel.com>

On Wed, Sep 29, 2021 at 12:03:36PM -0700, Dave Hansen wrote:
> On 9/29/21 11:58 AM, Alexander Popov wrote:
> > --- 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;

I like this idea. I can't tell if Linus would tolerate it, though. But I
really have wanted a middle ground like BUG(). Having only WARN() and
panic() is not very friendly. :(

> >  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);
> >  }
> 
> Doesn't this tie into the warning *printing* code?  That's better than
> nothing, for sure.  But, if we're doing this for hardening, I think we
> would want to kill anyone provoking a warning, not just the first one
> that triggered *printing* the warning.

Right, this needs to be moved into the callers of __warn() (i.e.
report_bug(), and warn_slowpath_fmt()), likely with some small
refactoring in report_bug().

-- 
Kees Cook