Re: [PATCH] lockdep: Make print_lock() address visible

["Paul E. McKenney" <paulmck@kernel.org>]

On Mon, Sep 16, 2019 at 08:07:55PM -0700, Kees Cook wrote:
> On Mon, Sep 16, 2019 at 06:39:46PM -0700, keescook@chromium.org wrote:
> > commit 519248f36d6f3c80e176f6fa844c10d94f1f5990
> > Author: Paul E. McKenney <paulmck@linux.ibm.com>
> > Date:   Thu May 30 05:39:25 2019 -0700
> > 
> >     lockdep: Make print_lock() address visible
> >     
> >     Security is a wonderful thing, but so is the ability to debug based on
> >     lockdep warnings.  This commit therefore makes lockdep lock addresses
> >     visible in the clear.
> >     
> >     Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
> > 
> > diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
> > index 4861cf8e274b..4aca3f4379d2 100644
> > --- a/kernel/locking/lockdep.c
> > +++ b/kernel/locking/lockdep.c
> > @@ -620,7 +620,7 @@ static void print_lock(struct held_lock *hlock)
> >  		return;
> >  	}
> >  
> > -	printk(KERN_CONT "%p", hlock->instance);
> > +	printk(KERN_CONT "%px", hlock->instance);
> >  	print_lock_name(lock);
> >  	printk(KERN_CONT ", at: %pS\n", (void *)hlock->acquire_ip);
> >  }
> 
> Just to clarify: this is only visible under CONFIG_LOCKDEP, yes? That's
> not a state anyone would run a production system under, I'd hope.

Yes, by my reading of kernel/locking/Makefile, the entire
kernel/locking/lockdep.c file is completely ignored unless
CONFIG_LOCKDEP=y.

So yes, it would be silly for this code to be in a production
system.

							Thanx, Paul