linux-kernel - Re: [PATCH 1/1] arch:hexagon/powerpc: use KSYM_NAME

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Message-ID: <ZHWub0ibU7etLnXK@alley>
Date:   Tue, 30 May 2023 10:06:07 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
Cc:     maninder1.s@...sung.com,
        "keescook@...omium.org" <keescook@...omium.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        "bcain@...cinc.com" <bcain@...cinc.com>,
        "mpe@...erman.id.au" <mpe@...erman.id.au>,
        "npiggin@...il.com" <npiggin@...il.com>,
        "christophe.leroy@...roup.eu" <christophe.leroy@...roup.eu>,
        "nathanl@...ux.ibm.com" <nathanl@...ux.ibm.com>,
        "ustavoars@...nel.org" <ustavoars@...nel.org>,
        "alex.gaynor@...il.com" <alex.gaynor@...il.com>,
        "gary@...yguo.net" <gary@...yguo.net>,
        "ojeda@...nel.org" <ojeda@...nel.org>,
        "linux-hexagon@...r.kernel.org" <linux-hexagon@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        Onkarnath <onkarnath.1@...sung.com>,
        Wedson Almeida Filho <wedsonaf@...il.com>
Subject: Re: [PATCH 1/1] arch:hexagon/powerpc: use KSYM_NAME_LEN in array size

On Mon 2023-05-29 16:50:45, Miguel Ojeda wrote:
> On Mon, May 29, 2023 at 1:08 PM Maninder Singh <maninder1.s@...sung.com> wrote:
> >
> > I Will add co-developed-by` tag.
> > because this change was identified while we were working on kallsyms some time back.
> > https://lore.kernel.org/lkml/YonTOL4zC4CytVrn@infradead.org/t/
> >
> > this patch set is pending and we will start working on that again, so i thought better
> > to send bugfix first.
> 
> Sounds good to me!
> 
> (Fixed Wedson's email address)
> 
> > Yes, I think second buffer was not related to kallsyms, so I have not touched that.
> 
> 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]);
>                                  ^      ~~~~~~~~~~~~~~~~~~~~~~
> 
> 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?.
> 
> Also, I went through the other callers to `kallsyms_lookup` to see
> other issues -- one I am not sure about is `fetch_store_symstring` in
> `kernel/trace/trace_probe_tmpl.h`. Steven/Masami: is that "with max
> length" in the function docs enough? Is it 0xffff?

The best solution would be to pass the buffer size as an extra
parameter. Especially when some code passes buffers that are
allocated/reserved dynamically.

Sigh, I am not sure how many changes it would require in kallsyms
API and all the callers. But it would be really appreciated, IMHO.

Best Regards,
Petr