linux-hardening - Re: [PATCH 3/5] codetag: Introduce codetag_early

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Message-ID: <CAJuCfpHLD=rK_xPpZ89t+E=S77dr=0Gq7+L9BLkojiqN+TC0FQ@mail.gmail.com>
Date: Thu, 29 Aug 2024 08:39:29 -0700
From: Suren Baghdasaryan <surenb@...gle.com>
To: Kees Cook <kees@...nel.org>
Cc: Vlastimil Babka <vbabka@...e.cz>, Kent Overstreet <kent.overstreet@...ux.dev>, 
	Christoph Lameter <cl@...ux.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>, linux-mm@...ck.org, 
	"GONG, Ruiqi" <gongruiqi@...weicloud.com>, Jann Horn <jannh@...gle.com>, 
	Matteo Rizzo <matteorizzo@...gle.com>, jvoisin <julien.voisin@...tri.org>, 
	Xiu Jianfeng <xiujianfeng@...wei.com>, linux-kernel@...r.kernel.org, 
	linux-hardening@...r.kernel.org
Subject: Re: [PATCH 3/5] codetag: Introduce codetag_early_walk()

On Fri, Aug 9, 2024 at 12:33 AM Kees Cook <kees@...nel.org> 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@...nel.org>
> ---
> Cc: Suren Baghdasaryan <surenb@...gle.com>
> Cc: Kent Overstreet <kent.overstreet@...ux.dev>
> Cc: Vlastimil Babka <vbabka@...e.cz>
> Cc: Christoph Lameter <cl@...ux.com>
> Cc: Pekka Enberg <penberg@...nel.org>
> Cc: David Rientjes <rientjes@...gle.com>
> Cc: Joonsoo Kim <iamjoonsoo.kim@....com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Roman Gushchin <roman.gushchin@...ux.dev>
> Cc: Hyeonggon Yoo <42.hyeyoo@...il.com>
> Cc: linux-mm@...ck.org
> ---
>  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).

> +
> +       for (ct = range.start; ct < range.stop; ct = ((void *)ct + desc->tag_size))
> +               callback(ct);
> +}
> +
>  static int codetag_module_init(struct codetag_type *cttype, struct module *mod)
>  {
>         struct codetag_range range;
> --
> 2.34.1
>