Re: [PATCH] Introduce the pkill_on_warn boot parameter

[Kees Cook]

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