linux-hardening - Re: [PATCH] slab: Decouple slab_debug and no_hash

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Message-ID: <f381d2f4-f86c-e714-c67a-1d060b8669d5@google.com>
Date: Sun, 13 Apr 2025 16:00:41 -0700 (PDT)
From: David Rientjes <rientjes@...gle.com>
To: Kees Cook <kees@...nel.org>
cc: Vlastimil Babka <vbabka@...e.cz>, 
    Sergio Perez Gonzalez <sperezglz@...il.com>, 
    Jonathan Corbet <corbet@....net>, Petr Mladek <pmladek@...e.com>, 
    Steven Rostedt <rostedt@...dmis.org>, 
    Andy Shevchenko <andriy.shevchenko@...ux.intel.com>, 
    Rasmus Villemoes <linux@...musvillemoes.dk>, 
    Sergey Senozhatsky <senozhatsky@...omium.org>, 
    Andrew Morton <akpm@...ux-foundation.org>, 
    Christoph Lameter <cl@...ux.com>, Pekka Enberg <penberg@...nel.org>, 
    Joonsoo Kim <iamjoonsoo.kim@....com>, 
    Roman Gushchin <roman.gushchin@...ux.dev>, 
    Harry Yoo <harry.yoo@...cle.com>, "Paul E. McKenney" <paulmck@...nel.org>, 
    Randy Dunlap <rdunlap@...radead.org>, Tamir Duberstein <tamird@...il.com>, 
    Miguel Ojeda <ojeda@...nel.org>, Alice Ryhl <aliceryhl@...gle.com>, 
    linux-doc@...r.kernel.org, linux-mm@...ck.org, 
    Thomas Huth <thuth@...hat.com>, "Borislav Petkov (AMD)" <bp@...en8.de>, 
    Ard Biesheuvel <ardb@...nel.org>, 
    Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
    Andreas Hindborg <a.hindborg@...nel.org>, 
    Stephen Boyd <swboyd@...omium.org>, linux-kernel@...r.kernel.org, 
    linux-hardening@...r.kernel.org
Subject: Re: [PATCH] slab: Decouple slab_debug and no_hash_pointers

On Thu, 10 Apr 2025, Kees Cook wrote:

> Some system owners use slab_debug=FPZ (or similar) as a hardening option,
> but do not want to be forced into having kernel addresses exposed due
> to the implicit "no_hash_pointers" boot param setting.[1]
> 
> Introduce the "hash_pointers" boot param, which defaults to "auto"
> (the current behavior), but also includes "always" (forcing on hashing
> even when "slab_debug=..." is defined), and "never". The existing
> "no_hash_pointers" boot param becomes an alias for "hash_pointers=never".
> 
> This makes it possible to boot with "slab_debug=FPZ hash_pointers=always".
> 
> Link: https://github.com/KSPP/linux/issues/368 [1]
> Fixes: 792702911f58 ("slub: force on no_hash_pointers when slub_debug is enabled")
> Co-developed-by: Sergio Perez Gonzalez <sperezglz@...il.com>
> Signed-off-by: Sergio Perez Gonzalez <sperezglz@...il.com>
> Signed-off-by: Kees Cook <kees@...nel.org>

Acked-by: David Rientjes <rientjes@...gle.com>