linux-hardening - Re: [PATCH v4 2/2] slab: Introduce kmalloc

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Message-ID: <CANpmjNMsSGY+QEn=GV8S2sXuuQsioikPR+OhGa3+6EoTqYPkHQ@mail.gmail.com>
Date: Tue, 7 Oct 2025 20:18:28 +0200
From: Marco Elver <elver@...gle.com>
To: "Christoph Lameter (Ampere)" <cl@...two.org>
Cc: Kees Cook <kees@...nel.org>, Matthew Wilcox <willy@...radead.org>, 
	Vlastimil Babka <vbabka@...e.cz>, Pekka Enberg <penberg@...nel.org>, 
	David Rientjes <rientjes@...gle.com>, Joonsoo Kim <iamjoonsoo.kim@....com>, 
	Andrew Morton <akpm@...ux-foundation.org>, Roman Gushchin <roman.gushchin@...ux.dev>, 
	Hyeonggon Yoo <42.hyeyoo@...il.com>, "Gustavo A . R . Silva" <gustavoars@...nel.org>, 
	Bill Wendling <morbo@...gle.com>, Justin Stitt <justinstitt@...gle.com>, Jann Horn <jannh@...gle.com>, 
	Przemek Kitszel <przemyslaw.kitszel@...el.com>, 
	Linus Torvalds <torvalds@...ux-foundation.org>, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Sasha Levin <sashal@...nel.org>, linux-mm@...ck.org, 
	Miguel Ojeda <ojeda@...nel.org>, Nathan Chancellor <nathan@...nel.org>, 
	Peter Zijlstra <peterz@...radead.org>, Nick Desaulniers <nick.desaulniers+lkml@...il.com>, 
	Jonathan Corbet <corbet@....net>, Jakub Kicinski <kuba@...nel.org>, Yafang Shao <laoar.shao@...il.com>, 
	Tony Ambardar <tony.ambardar@...il.com>, Alexander Lobakin <aleksander.lobakin@...el.com>, 
	Jan Hendrik Farr <kernel@...rr.cc>, Alexander Potapenko <glider@...gle.com>, linux-kernel@...r.kernel.org, 
	linux-hardening@...r.kernel.org, linux-doc@...r.kernel.org, 
	llvm@...ts.linux.dev, Matteo Rizzo <matteorizzo@...gle.com>
Subject: Re: [PATCH v4 2/2] slab: Introduce kmalloc_obj() and family

On Tue, 7 Oct 2025 at 19:47, Christoph Lameter (Ampere) <cl@...two.org> wrote:
>
> On Tue, 7 Oct 2025, Kees Cook wrote:
>
> > But all of that is orthogonal to just _having_ the type info available.
>
> iOS did go the path of creating basically one slab cache for each
> "type" of kmalloc for security reasons.
>
> See https://security.apple.com/blog/towards-the-next-generation-of-xnu-memory-safety/

We can get something similar to that with:
https://lore.kernel.org/all/20250825154505.1558444-1-elver@google.com/
Pending compiler support which is going to become available in a few
months (probably).
That version used the existing RANDOM_KMALLOC_CACHES choice of 16 slab
caches, but there's no fundamental limitation to go higher.
Note, this mitigation is likely not as strong as we'd like to without
SLAB_VIRTUAL (or so I'm told): https://lwn.net/Articles/944647/