linux-kernel - Re: [PATCH v8 4/4] vsprintf: Add command line option debug_boot_weak

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Message-ID: <20180620223014.GE11671@eros>
Date:   Thu, 21 Jun 2018 08:30:14 +1000
From:   "Tobin C. Harding" <me@...in.cc>
To:     Randy Dunlap <rdunlap@...radead.org>
Cc:     Theodore Ts'o <tytso@....edu>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Kees Cook <keescook@...omium.org>,
        Anna-Maria Gleixner <anna-maria@...utronix.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Arnd Bergmann <arnd@...db.de>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 4/4] vsprintf: Add command line option
 debug_boot_weak_hash

On Wed, Jun 20, 2018 at 09:09:49AM -0700, Randy Dunlap wrote:
> On 06/19/2018 09:20 PM, Tobin C. Harding wrote:
> > Currently printing [hashed] pointers requires enough entropy to be
> > available.  Early in the boot sequence this may not be the case
> > resulting in a dummy string '(____ptrval____)' being printed.  This
> > makes debugging the early boot sequence difficult.  We can relax the
> > requirement to use cryptographically secure hashing during debugging.
> > This enables debugging while keeping development/production kernel
> > behaviour the same.
> > 
> > If new command line option debug_boot_weak_hash is enabled use
> > cryptographically insecure hashing and hash pointer value immediately.
> > 
> > Signed-off-by: Tobin C. Harding <me@...in.cc>
> > Reviewed-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
> > ---
> >  Documentation/admin-guide/kernel-parameters.txt |  9 +++++++++
> >  lib/vsprintf.c                                  | 17 +++++++++++++++++
> >  2 files changed, 26 insertions(+)
> > 
> > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> > index 638342d0a095..a116fc0366b0 100644
> > --- a/Documentation/admin-guide/kernel-parameters.txt
> > +++ b/Documentation/admin-guide/kernel-parameters.txt
> > @@ -748,6 +748,15 @@
> >  
> >  	debug		[KNL] Enable kernel debugging (events log level).
> >  
> > +	debug_boot_weak_hash
> > +			[KNL] Enable printing pointers early in the boot
> > +			sequence.  If enabled, we use a weak hash instead of
> > +			siphash to hash pointers.  Use this option if you need
> > +			to see pointer values during early boot (i.e you are
> 
> maybe:
> 			to see hashed pointer values
> i.e., not raw pointers.

You cannot see 'raw pointers' anyways?

> 
> > +			seeing instances of '(___ptrval___)').
> > +			Cryptographically insecure, please do not use on
> > +			production kernels.

thanks for the review, I don't quiet see how to use your suggestion to
make the text clearer.  If you still feel this change is needed perhaps
you could write so I understand i.e 'Use this option if ...'


thanks,
Tobin.