Re: [PATCH] Revert "slub: force on no_hash_pointers when slub_debug is enabled"

[Hyeonggon Yoo]

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@xxxxxxx>
> Cc: Stephen Boyd <swboyd@xxxxxxxxxxxx>
> Cc: concord@xxxxxxxxxx
> Cc: Pekka Enberg <penberg@xxxxxxxxxx>
> Cc: David Rientjes <rientjes@xxxxxxxxxx>
> Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
> Cc: Petr Mladek <pmladek@xxxxxxxx>
> Cc: linux-mm@xxxxxxxxx
> Cc: stable@xxxxxxxxxxxxxxx
> Link: https://lore.kernel.org/lkml/202109200726.2EFEDC5@keescook/
> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>

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?