Re: [PATCH 1/1] arch:hexagon/powerpc: use KSYM_NAME_LEN in array size

[Miguel Ojeda]

On Wed, May 31, 2023 at 1:14 AM Kees Cook <keescook@xxxxxxxxxxxx> wrote:
>
> On Mon, May 29, 2023 at 04:50:45PM +0200, Miguel Ojeda wrote:
> > Kees: what is the current stance on `[static N]` parameters? Something like:
> >
> >     const char *kallsyms_lookup(unsigned long addr,
> >                                 unsigned long *symbolsize,
> >                                 unsigned long *offset,
> >     -                           char **modname, char *namebuf);
> >     +                           char **modname, char namebuf[static KSYM_NAME_LEN]);
> >
> > makes the compiler complain about cases like these (even if trivial):
> >
> >     arch/powerpc/xmon/xmon.c:1711:10: error: array argument is too small;
> >         contains 128 elements, callee requires at least 512
> > [-Werror,-Warray-bounds]
> >             name = kallsyms_lookup(pc, &size, &offset, NULL, tmpstr);
> >                  ^                                           ~~~~~~
> >     ./include/linux/kallsyms.h:86:29: note: callee declares array
> > parameter as static here
> >             char **modname, char namebuf[static KSYM_NAME_LEN]);
> >                                  ^      ~~~~~~~~~~~~~~~~~~~~~~
>
> Wouldn't that be a good thing? (I.e. complain about the size mismatch?)

Yeah, I would say so (i.e. I meant it as a good thing).

> > But I only see 2 files in the kernel using `[static N]` (from 2020 and
> > 2021). Should something else be used instead (e.g. `__counted_by`),
> > even if constexpr-sized?.
>
> Yeah, it seems pretty uncommon. I'd say traditionally arrays aren't
> based too often, rather structs containing them.
>
> But ultimately, yeah, everything could gain __counted_by and friends in
> the future.

That would be nice!

Cheers,
Miguel