linux-kernel - Re: [PATCH 2/2] memblock: annotate struct memblock_type with __counted_by

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Message-Id: <20251122141614.80f1a845cd694b1b470107ca@linux-foundation.org>
Date: Sat, 22 Nov 2025 14:16:14 -0800
From: Andrew Morton <akpm@...ux-foundation.org>
To: Kees Cook <kees@...nel.org>
Cc: Bill Wendling <morbo@...gle.com>, linux-kernel@...r.kernel.org,
 "Gustavo A. R. Silva" <gustavoars@...nel.org>, Nathan Chancellor
 <nathan@...nel.org>, Nick Desaulniers <nick.desaulniers+lkml@...il.com>,
 Justin Stitt <justinstitt@...gle.com>, Miguel Ojeda <ojeda@...nel.org>,
 Peter Zijlstra <peterz@...radead.org>, Heiko Carstens <hca@...ux.ibm.com>,
 Marc Herbert <Marc.Herbert@...ux.intel.com>, Uros Bizjak
 <ubizjak@...il.com>, Tejun Heo <tj@...nel.org>, Jeff Xu
 <jeffxu@...omium.org>, Michal Koutný <mkoutny@...e.com>,
 Shakeel Butt <shakeel.butt@...ux.dev>, Thomas Weißschuh
 <thomas.weissschuh@...utronix.de>, John Stultz <jstultz@...gle.com>,
 Christian Brauner <brauner@...nel.org>, Randy Dunlap
 <rdunlap@...radead.org>, Brian Gerst <brgerst@...il.com>, Masahiro Yamada
 <masahiroy@...nel.org>, Mike Rapoport <rppt@...nel.org>,
 linux-mm@...ck.org, linux-hardening@...r.kernel.org, llvm@...ts.linux.dev
Subject: Re: [PATCH 2/2] memblock: annotate struct memblock_type with
 __counted_by_ptr

On Fri, 21 Nov 2025 16:30:43 -0800 Kees Cook <kees@...nel.org> wrote:

> On Fri, Nov 21, 2025 at 07:39:44PM +0000, Bill Wendling wrote:
> > Add the '__counted_by_ptr' attribute to the 'regions' field of 'struct
> > memblock_type'. The 'regions' field is an array of 'struct
> > memblock_region' and its size is tracked by the 'max' field, which
> > represents the total number of allocated regions.
> 
> As part of any counted_by annotation patch, there needs to be discussion
> in the commit log about how it's been shown to be a safe annotation
> to make. e.g. in this case, if all allocations of "regions" have a
> corresponding "max" assignment, etc. If just "git grep" can't find them
> all, using something like Coccinelle or CodeQL to search for struct
> memblock_type::regions assignments can work.

How is anyone to know these things?  I can't find anything about this
in include/ or Documentation/ or in the relevant commits.

There should be a comment at the __counted_by() definition site, please.

And possibly write a Documentation/ file then change checkpatch to
direct people to that file if they add a counted_by?