linux-hardening - Re: [RFC][PATCH 0/4] slab: Allow for type introspection during allocation

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Message-ID: <202407091626.055933E3@keescook>
Date: Tue, 9 Jul 2024 16:28:31 -0700
From: Kees Cook <kees@...nel.org>
To: Marco Elver <elver@...gle.com>
Cc: "Christoph Lameter (Ampere)" <cl@...two.org>,
	Vlastimil Babka <vbabka@...e.cz>, Jann Horn <jannh@...gle.com>,
	Tony Luck <tony.luck@...el.com>,
	Nick Desaulniers <ndesaulniers@...gle.com>,
	Miguel Ojeda <ojeda@...nel.org>,
	Nathan Chancellor <nathan@...nel.org>, Hao Luo <haoluo@...gle.com>,
	Przemek Kitszel <przemyslaw.kitszel@...el.com>,
	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>,
	"Guilherme G. Piccoli" <gpiccoli@...lia.com>,
	Mark Rutland <mark.rutland@....com>,
	Jakub Kicinski <kuba@...nel.org>, Petr Pavlu <petr.pavlu@...e.com>,
	Alexander Lobakin <aleksander.lobakin@...el.com>,
	Tony Ambardar <tony.ambardar@...il.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	linux-hardening@...r.kernel.org
Subject: Re: [RFC][PATCH 0/4] slab: Allow for type introspection during
 allocation

On Tue, Jul 09, 2024 at 11:02:55PM +0200, Marco Elver wrote:
> On Tue, 9 Jul 2024 at 22:28, Kees Cook <kees@...nel.org> wrote:
> >
> > On Tue, Jul 09, 2024 at 10:26:32AM -0700, Christoph Lameter (Ampere) wrote:
> > > On Mon, 8 Jul 2024, Kees Cook wrote:
> > >
> > > >
> > > >            obj = kmalloc(obj, gfp);
> > >
> > > Could we avoid repeating "obj" in this pattern?
> > >
> > > F.e.
> > >
> > >       KMALLOC(obj, gfp);
> >
> > This appears to be the common feedback, which is good! :) And we can
> > still have it return "obj" as well, so it could still be used in
> > "return" statements, etc. I will work up a new RFC...
> 
> More macros like this only obfuscate the code further. The name would
> become something that makes it really clear there's an assignment.
> 
>   assign_kmalloc(obj, gfp)
> 
> There may be better options. Also ALLCAPS could be avoided here, as we
> have done with other language-like features (vs. pure constants).

So, in looking a code patterns, it seems what we really want more than
returning the object that was allocated is actually returning the size
of the allocation size requested. i.e.:

	info->size = struct_size(ptr, flex_member, count);
	info->obj = kmalloc(info->size, gfp);

would become:

	info->size = kmalloc(info->obj, flex_member, count, gfp);

-Kees

-- 
Kees Cook