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Date: Tue, 7 Nov 2017 17:44:13 -0500
From: Steven Rostedt <rostedt@...dmis.org>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: 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>, Peter Zijlstra
 <peterz@...radead.org>
Subject: Re: [PATCH v3] scripts: add leaking_addresses.pl

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?

-- Steve

> 
> Profiling you often *cannot* do as root - some things you profile
> really shouldn't be run as root, and might even refuse to do so. So
> requiring you to be root just to get a kernel profile is very bad.
> 
> But looking at lockdep stats? Yeah, 'sudo' isn't so big of a deal.
> 
> 

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