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

Randy Dunlap
2018-06-20T16:09:59Z

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.

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

thanks,
--
~Randy