linux-hardening - Re: [PATCH] Revert "slub: force on no_hash_pointers when slub

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Date:   Wed, 8 Feb 2023 23:58:54 +0000
From:   Hyeonggon Yoo <42.hyeyoo@...il.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Vlastimil Babka <vbabka@...e.cz>,
        Stephen Boyd <swboyd@...omium.org>, concord@...too.org,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Petr Mladek <pmladek@...e.com>, linux-mm@...ck.org,
        stable@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Christoph Lameter <cl@...ux.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Keith Busch <kbusch@...nel.org>, Jens Axboe <axboe@...nel.dk>,
        Bart Van Assche <bvanassche@....org>,
        Mikulas Patocka <mpatocka@...hat.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] Revert "slub: force on no_hash_pointers when slub_debug
 is enabled"

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@...e.cz>
> Cc: Stephen Boyd <swboyd@...omium.org>
> Cc: concord@...too.org
> Cc: Pekka Enberg <penberg@...nel.org>
> Cc: David Rientjes <rientjes@...gle.com>
> Cc: Joonsoo Kim <iamjoonsoo.kim@....com>
> Cc: Petr Mladek <pmladek@...e.com>
> Cc: linux-mm@...ck.org
> Cc: stable@...r.kernel.org
> Link: https://lore.kernel.org/lkml/202109200726.2EFEDC5@keescook/
> Signed-off-by: Kees Cook <keescook@...omium.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?