Re: [PATCH v6 4/4] vsprintf: Add command line option debug_boot_weak_hash

Randy Dunlap
2018-05-28T17:40:53Z

On 05/27/2018 06:46 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.
>
> Cc: Anna-Maria Gleixner <anna-maria@linutronix.de>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Randy Dunlap <rdunlap@infradead.org>
> Signed-off-by: Tobin C. Harding <me@tobin.cc>
> ---
> Documentation/admin-guide/kernel-parameters.txt | 9 +++++++++
> lib/vsprintf.c | 20 ++++++++++++++++++++
> 2 files changed, 29 insertions(+)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index f2040d46f095..8a86d895343e 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -753,6 +753,15 @@
>
> debug [KNL] Enable kernel debugging (events log level).
>

Hi,
This is much more readable than the previous version. Thanks.

> + 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

i.e.

> + seeing instances of '(___ptrval___)').
> + Cryptographically insecure, please do not use on
> + production kernels.
> +
> debug_locks_verbose=
> [KNL] verbose self-tests
> Format=<0|1>

--
~Randy