linux-kernel - Re: [PATCH v3] scripts: add leaking

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Date:   Wed, 8 Nov 2017 09:20:08 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Kees Cook <keescook@...omium.org>,
        "Tobin C. Harding" <me@...in.cc>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Andy Lutomirski <luto@...nel.org>,
        Joe Perches <joe@...ches.com>,
        Network Development <netdev@...r.kernel.org>,
        David Miller <davem@...emloft.net>,
        "kernel-hardening@...ts.openwall.com" 
        <kernel-hardening@...ts.openwall.com>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        Theodore Ts'o <tytso@....edu>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Tycho Andersen <tycho@...ker.com>,
        "Roberts, William C" <william.c.roberts@...el.com>,
        Tejun Heo <tj@...nel.org>,
        Jordan Glover <Golden_Miller83@...tonmail.ch>,
        Greg KH <gregkh@...uxfoundation.org>,
        Petr Mladek <pmladek@...e.com>,
        Ian Campbell <ijc@...lion.org.uk>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <wilal.deacon@....com>,
        Chris Fries <cfries@...gle.com>,
        Dave Weinstein <olorin@...gle.com>,
        Daniel Micay <danielmicay@...il.com>,
        Djalal Harouni <tixxdz@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] scripts: add leaking_addresses.pl

On Tue, Nov 07, 2017 at 05:44:13PM -0500, Steven Rostedt wrote:
> On Tue, 7 Nov 2017 13:44:01 -0800
> Linus Torvalds <torvalds@...ux-foundation.org> wrote:
> 
> > > Looking other places that stand out, it seems like
> > > /proc/lockdep_chains and /proc/lockdep (CONFIG_LOCKDEP=y) has a ton of
> > > %p usage. It's unclear to me if a hash is sufficient for meaningful
> > > debugging there?  
> > 
> > Maybe not, but that is also _so_ esoteric that I suspect the right fix
> > is to just make it root-only readable.
> 
> Also note, I don't believe anyone should be running a LOCKDEP
> configured kernel in a production (secured) environment. As it adds
> quite a bit of overhead. It's something you run on test environments to
> make sure it doesn't detect any possible deadlocks.
> 
> > 
> > I've never used it, we should check with people who have. I get the
> > feeling that this is purely for PeterZ debugging.
> 
> I've used it. But then again, I also debug lockdep ;-)
> 
> > 
> > The very first commit that introduced that code actually has a
> > 
> >     (FIXME: should go into debugfs)
> > 
> > so I suspect it never should have been user-readable to begin with. I
> > guess it makes some things easier, but it really is *very* different
> > from things like profiling.
> 
> Want me to whip up a patch to move the file?

Fine by me; create /debug/lockdep/ for the 3 files or something like
that.

As to the actual addresses, they can be used to double check things are
in fact the same object (in case of name collisions), are in static
memory (as these things ought to be) etc.. But mostly they're not too
important.

And yes, as everybody says, LOCKDEP is debug tool; you run this on your
(local) dev kernels, anything else it out of spec.