linux-kernel - Re: [PATCH 3/6] kallsyms/bpf: Set module buildid in bpf_address

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Message-ID: <CAADnVQ+kbQ4uwtKjD1DRCf702v0rEthy6hU4COAU9CyU53wTHg@mail.gmail.com>
Date: Wed, 5 Nov 2025 18:53:23 -0800
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Petr Mladek <pmladek@...e.com>
Cc: Petr Pavlu <petr.pavlu@...e.com>, Steven Rostedt <rostedt@...dmis.org>, 
	Alexei Starovoitov <ast@...nel.org>, Andrew Morton <akpm@...ux-foundation.org>, Kees Cook <kees@...nel.org>, 
	Daniel Borkmann <daniel@...earbox.net>, John Fastabend <john.fastabend@...il.com>, 
	Masami Hiramatsu <mhiramat@...nel.org>, Mark Rutland <mark.rutland@....com>, 
	Luis Chamberlain <mcgrof@...nel.org>, Daniel Gomez <da.gomez@...nel.org>, 
	Sami Tolvanen <samitolvanen@...gle.com>, LKML <linux-kernel@...r.kernel.org>, 
	bpf <bpf@...r.kernel.org>, linux-modules@...r.kernel.org, 
	linux-trace-kernel <linux-trace-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/6] kallsyms/bpf: Set module buildid in bpf_address_lookup()

On Wed, Nov 5, 2025 at 6:24 AM Petr Mladek <pmladek@...e.com> wrote:
>
> Make bpf_address_lookup() compatible with module_address_lookup()
> and clear the pointer to @modbuildid together with @modname.
>
> It is not strictly needed because __sprint_symbol() reads @modbuildid
> only when @modname is set. But better be on the safe side and make
> the API more safe.
>
> Fixes: 9294523e3768 ("module: add printk formats to add module build ID to stacktraces")
> Signed-off-by: Petr Mladek <pmladek@...e.com>
> ---
>  include/linux/filter.h | 15 +++++++++++----
>  kernel/kallsyms.c      |  4 ++--
>  2 files changed, 13 insertions(+), 6 deletions(-)
>
> diff --git a/include/linux/filter.h b/include/linux/filter.h
> index f5c859b8131a..b7b95840250a 100644
> --- a/include/linux/filter.h
> +++ b/include/linux/filter.h
> @@ -1362,12 +1362,18 @@ struct bpf_prog *bpf_prog_ksym_find(unsigned long addr);
>
>  static inline int
>  bpf_address_lookup(unsigned long addr, unsigned long *size,
> -                  unsigned long *off, char **modname, char *sym)
> +                  unsigned long *off, char **modname,
> +                  const unsigned char **modbuildid, char *sym)
>  {
>         int ret = __bpf_address_lookup(addr, size, off, sym);
>
> -       if (ret && modname)
> -               *modname = NULL;
> +       if (ret) {
> +               if (modname)
> +                       *modname = NULL;
> +               if (modbuildid)
> +                       *modbuildid = NULL;
> +       }
> +
>         return ret;
>  }
>
> @@ -1433,7 +1439,8 @@ static inline struct bpf_prog *bpf_prog_ksym_find(unsigned long addr)
>
>  static inline int
>  bpf_address_lookup(unsigned long addr, unsigned long *size,
> -                  unsigned long *off, char **modname, char *sym)
> +                  unsigned long *off, char **modname,
> +                  const unsigned char **modbuildid, char *sym)
>  {
>         return 0;
>  }
> diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
> index 9455e3bb07fc..efb12b077220 100644
> --- a/kernel/kallsyms.c
> +++ b/kernel/kallsyms.c
> @@ -374,8 +374,8 @@ static int kallsyms_lookup_buildid(unsigned long addr,
>         ret = module_address_lookup(addr, symbolsize, offset,
>                                     modname, modbuildid, namebuf);
>         if (!ret)
> -               ret = bpf_address_lookup(addr, symbolsize,
> -                                        offset, modname, namebuf);
> +               ret = bpf_address_lookup(addr, symbolsize, offset,
> +                                        modname, modbuildid, namebuf);

The initial bpf_address_lookup() 8 years ago was trying
to copy paste args and style of kallsyms_lookup().
It was odd back then. This change is doubling down on the wrong thing.
It's really odd to pass a pointer into bpf_address_lookup()
so it zero initializes it.
bpf ksyms are in the core kernel. They're never in modules.
Just call __bpf_address_lookup() here and remove the wrapper.