linux-kernel - Re: [PATCH v6 4/4] vsprintf: Add command line option debug_boot_weak

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Message-ID: <fde2cc84-f1d8-b1ee-510b-b3659834874d@infradead.org>
Date:   Mon, 28 May 2018 10:40:43 -0700
From:   Randy Dunlap <rdunlap@...radead.org>
To:     "Tobin C. Harding" <me@...in.cc>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Kees Cook <keescook@...omium.org>,
        Anna-Maria Gleixner <anna-maria@...utronix.de>,
        Theodore Ts'o <tytso@....edu>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Arnd Bergmann <arnd@...db.de>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 4/4] vsprintf: Add command line option
 debug_boot_weak_hash

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@...utronix.de>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Cc: Randy Dunlap <rdunlap@...radead.org>
> Signed-off-by: Tobin C. Harding <me@...in.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