linux-hardening - Re: [RFC PATCH] mm/damon/sysfs: add __counted

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Date:   Sat, 26 Aug 2023 00:54:47 +0000
From:   SeongJae Park <sj@...nel.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     SeongJae Park <sj@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        damon@...ts.linux.dev, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Qing Zhao <qing.zhao@...cle.com>,
        linux-hardening@...r.kernel.org
Subject: Re: [RFC PATCH] mm/damon/sysfs: add __counted_by() annotation

Hi Kees,

On Fri, 25 Aug 2023 14:32:34 -0700 Kees Cook <keescook@...omium.org> wrote:

> On Fri, Aug 25, 2023 at 02:04:41AM +0000, SeongJae Park wrote:
> > Commit dd06e72e68bc ("Compiler Attributes: Add __counted_by macro")
> > added __counted_by() annotation.  The underlying attribute for the
> > feature is still under development, but adopting it can improve the
> > readability of the code.  Apply it to four dynamic arrays in DAMON sysfs
> > code.
> > 
> > Signed-off-by: SeongJae Park <sj@...nel.org>
> > ---
> >  mm/damon/sysfs.c | 8 ++++----
> >  1 file changed, 4 insertions(+), 4 deletions(-)
> > 
> > diff --git a/mm/damon/sysfs.c b/mm/damon/sysfs.c
> > index 808a8efe0523..36a176f38726 100644
> > --- a/mm/damon/sysfs.c
> > +++ b/mm/damon/sysfs.c
> > @@ -93,7 +93,7 @@ static const struct kobj_type damon_sysfs_region_ktype = {
> > 
> >  struct damon_sysfs_regions {
> >  	struct kobject kobj;
> > -	struct damon_sysfs_region **regions_arr;
> > +	struct damon_sysfs_region **regions_arr __counted_by(nr);
> >  	int nr;
> >  };
> 
> Unfortunately this isn't supported yet for non-flexible-array-members:
> 
> mm/damon/sysfs.c:96:14: error: 'counted_by' attribute may not be specified for a non-array field
>    96 |         struct damon_sysfs_region **regions_arr __counted_by(nr);
>       |                                     ^~~~~
> 
> We'll have to wait a bit before we can add this patch.

Thank you for checking this and let me know.  Ok, I will wait.

> Thank you for
> getting it ready, though!

Owing to your previous contributions.  Thank you for helping me make DAMON code
better to read :)

> This support is next in line. :)
> 
> The FAM support is likely ready to land, though[1]. I just tested it
> today.
> 
> -Kees
> 
> [1] https://gcc.gnu.org/pipermail/gcc-patches/2023-August/628459.html
> 
> -- 
> Kees Cook
> 


Thanks,
SJ