Re: [PATCH 2/2] memblock: annotate struct memblock_type with __counted_by_ptr

[Bill Wendling <morbo@google.com>]

On Mon, Nov 24, 2025 at 11:19 AM Kees Cook <kees@kernel.org> wrote:
>
> On Sat, Nov 22, 2025 at 02:16:14PM -0800, Andrew Morton wrote:
> > On Fri, 21 Nov 2025 16:30:43 -0800 Kees Cook <kees@kernel.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?
>
> This is a fair point, yes. The documentation and discussions around
> counted_by are very big in my mind (and for Bill), so it was mostly a
> consolidation/reminder and some extra detail on prior solutions, but
> for anyone new to that annotation, we should have collected common
> guidance. I will write something up.
>
Good point. I'll add documentation for these attributes both in
Documentation/ and at the macro site. The frustrating thing is that
we're likely to have at least one other macro flavor (something like
"__counted_by_expr"), though that's the only foreseeable one. All of
these macros are wrappers around the same attribute because of
compiler skew.

-bw