Re: [PATCH v8 4/4] vsprintf: Add command line option debug_boot_weak_hash

Tobin C. Harding
2018-06-20T22:30:24Z

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@tobin.cc>
> > Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.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.