Date:   Wed, 8 Feb 2023 23:58:54 +0000
From:   Hyeonggon Yoo <42.hyeyoo@gmail.com>
To:     Kees Cook <keescook@chromium.org>
Cc:     Vlastimil Babka <vbabka@suse.cz>,
        Stephen Boyd <swboyd@chromium.org>, concord@gentoo.org,
        Pekka Enberg <penberg@kernel.org>,
        David Rientjes <rientjes@google.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Petr Mladek <pmladek@suse.com>, linux-mm@kvack.org,
        stable@vger.kernel.org, Steven Rostedt <rostedt@goodmis.org>,
        Sergey Senozhatsky <senozhatsky@chromium.org>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Rasmus Villemoes <linux@rasmusvillemoes.dk>,
        Christoph Lameter <cl@linux.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Roman Gushchin <roman.gushchin@linux.dev>,
        Keith Busch <kbusch@kernel.org>, Jens Axboe <axboe@kernel.dk>,
        Bart Van Assche <bvanassche@acm.org>,
        Mikulas Patocka <mpatocka@redhat.com>,
        Ard Biesheuvel <ardb@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org
Subject: Re: [PATCH] Revert "slub: force on no_hash_pointers when slub_debug
 is enabled"
Message-ID: <Y+Q2xVKiN9UdZGwA@localhost>
References: <20230208194712.never.999-kees@kernel.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20230208194712.never.999-kees@kernel.org>
Precedence: bulk

On Wed, Feb 08, 2023 at 11:47:17AM -0800, Kees Cook wrote:
> This reverts commit 792702911f581f7793962fbeb99d5c3a1b28f4c3.
> 
> Linking no_hash_pointers() to slub_debug has had a chilling effect
> on using slub_debug features for security hardening, since system
> builders are forced to choose between redzoning and heap address location
> exposures. Instead, just require that the "no_hash_pointers" boot param
> needs to be used to expose pointers during slub_debug reports.
> 
> Cc: Vlastimil Babka <vbabka@suse.cz>
> Cc: Stephen Boyd <swboyd@chromium.org>
> Cc: concord@gentoo.org
> Cc: Pekka Enberg <penberg@kernel.org>
> Cc: David Rientjes <rientjes@google.com>
> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
> Cc: Petr Mladek <pmladek@suse.com>
> Cc: linux-mm@kvack.org
> Cc: stable@vger.kernel.org
> Link: https://lore.kernel.org/lkml/202109200726.2EFEDC5@keescook/
> Signed-off-by: Kees Cook <keescook@chromium.org>

in the commit message:

> Obscuring the pointers that slub shows when debugging makes for some
> confusing slub debug messages:
>
> Padding overwritten. 0x0000000079f0674a-0x000000000d4dce17
>
> Those addresses are hashed for kernel security reasons. If we're trying
> to be secure with slub_debug on the commandline we have some big
> problems given that we dump whole chunks of kernel memory to the kernel
> logs.

it dumps parts of kernel memory anyway and I'm not sure if slub_debug is
supposed to be used for security hardening.

what about introducing new boot parameter like, slub_hardening,
which does not print anything?