Re: [PATCH 3/5] codetag: Introduce codetag_early_walk()

[Kees Cook]

On Thu, Aug 29, 2024 at 08:39:29AM -0700, Suren Baghdasaryan wrote:
> On Fri, Aug 9, 2024 at 12:33 AM Kees Cook <kees@xxxxxxxxxx> wrote:
> >
> > In order to process builtin alloc_tags much earlier during boot (before
> > register_codetag() is processed), provide codetag_early_walk() that
> > perform a lockless walk with a specified callback function. This will be
> > used to allocate required caches that cannot be allocated on demand.
> >
> > Signed-off-by: Kees Cook <kees@xxxxxxxxxx>
> > ---
> > Cc: Suren Baghdasaryan <surenb@xxxxxxxxxx>
> > Cc: Kent Overstreet <kent.overstreet@xxxxxxxxx>
> > Cc: Vlastimil Babka <vbabka@xxxxxxx>
> > Cc: Christoph Lameter <cl@xxxxxxxxx>
> > Cc: Pekka Enberg <penberg@xxxxxxxxxx>
> > Cc: David Rientjes <rientjes@xxxxxxxxxx>
> > Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
> > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> > Cc: Roman Gushchin <roman.gushchin@xxxxxxxxx>
> > Cc: Hyeonggon Yoo <42.hyeyoo@xxxxxxxxx>
> > Cc: linux-mm@xxxxxxxxx
> > ---
> >  include/linux/codetag.h |  2 ++
> >  lib/codetag.c           | 16 ++++++++++++++++
> >  2 files changed, 18 insertions(+)
> >
> > diff --git a/include/linux/codetag.h b/include/linux/codetag.h
> > index c2a579ccd455..9eb1fcd90570 100644
> > --- a/include/linux/codetag.h
> > +++ b/include/linux/codetag.h
> > @@ -64,6 +64,8 @@ void codetag_lock_module_list(struct codetag_type *cttype, bool lock);
> >  bool codetag_trylock_module_list(struct codetag_type *cttype);
> >  struct codetag_iterator codetag_get_ct_iter(struct codetag_type *cttype);
> >  struct codetag *codetag_next_ct(struct codetag_iterator *iter);
> > +void codetag_early_walk(const struct codetag_type_desc *desc,
> > +                       void (*callback)(struct codetag *ct));
> >
> >  void codetag_to_text(struct seq_buf *out, struct codetag *ct);
> >
> > diff --git a/lib/codetag.c b/lib/codetag.c
> > index ef7634c7ee18..9d563c8c088a 100644
> > --- a/lib/codetag.c
> > +++ b/lib/codetag.c
> > @@ -154,6 +154,22 @@ static struct codetag_range get_section_range(struct module *mod,
> >         };
> >  }
> >
> > +void codetag_early_walk(const struct codetag_type_desc *desc,
> > +                       void (*callback)(struct codetag *ct))
> > +{
> > +       struct codetag_range range;
> > +       struct codetag *ct;
> > +
> > +       range = get_section_range(NULL, desc->section);
> > +       if (!range.start || !range.stop ||
> > +           range.start == range.stop ||
> > +           range.start > range.stop)
> > +               return;
> 
> I think this check can be simplified to:
> 
>         if (!range.start || range.start >= range.stop)
>                 return;
> 
> nit: Technically (!range.start) should also never trigger. In a valid
> image these symbols are either missing (range.start == range.stop ==
> NULL) or both are defined and (range.start < range.stop).

Yeah, all true. I was mainly copying all the checks that existed in the
"slow path" version.

I will adjust this for the next version.

-- 
Kees Cook