linux-kernel - Re: [PATCH v4 2/3] bpf: make bpf_dump_raw_ok() based on CONFIG

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Date:   Tue, 6 Jun 2023 10:08:42 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Maninder Singh <maninder1.s@...sung.com>
Cc:     ast@...nel.org, daniel@...earbox.net, john.fastabend@...il.com,
        andrii@...nel.org, martin.lau@...ux.dev, song@...nel.org,
        yhs@...com, kpsingh@...nel.org, sdf@...gle.com, haoluo@...gle.com,
        jolsa@...nel.org, thunder.leizhen@...wei.com, mcgrof@...nel.org,
        boqun.feng@...il.com, vincenzopalazzodev@...il.com,
        ojeda@...nel.org, jgross@...e.com, brauner@...nel.org,
        michael.christie@...cle.com, samitolvanen@...gle.com,
        glider@...gle.com, peterz@...radead.org, keescook@...omium.org,
        stephen.s.brennan@...cle.com, alan.maguire@...cle.com,
        pmladek@...e.com, linux-kernel@...r.kernel.org,
        bpf@...r.kernel.org, Onkarnath <onkarnath.1@...sung.com>
Subject: Re: [PATCH v4 2/3] bpf: make bpf_dump_raw_ok() based on CONFIG_KALLSYMS

On Mon, Jun 5, 2023 at 9:28 PM Maninder Singh <maninder1.s@...sung.com> wrote:
>
> bpf_dump_raw_ok() depends on kallsyms_show_value() and we already
> have a false definition for the !CONFIG_KALLSYMS case. But we'll
> soon expand on kallsyms_show_value() and so to make the code
> easier to follow just provide a direct !CONFIG_KALLSYMS definition
> for bpf_dump_raw_ok() as well.

I'm sorry, I'm failing to follow the exact reasoning about
simplification. It seems simpler to have

static inline bool kallsyms_show_value(const struct cred *cred)
{
    return false;
}

and control it from kallsyms-related internal header, rather than
adding CONFIG_KALLSYMS ifdef-ery to include/linux/filter.h and
redefining that `return false` decision. What if in the future we
decide that if !CONFIG_KALLSYMS it's ok to show raw addresses, now
we'll have to remember to update it in two places.

Unless I'm missing some other complications?

>
> Co-developed-by: Onkarnath <onkarnath.1@...sung.com>
> Signed-off-by: Onkarnath <onkarnath.1@...sung.com>
> Signed-off-by: Maninder Singh <maninder1.s@...sung.com>
> Reviewed-by: Luis Chamberlain <mcgrof@...nel.org>
> ---
>  include/linux/filter.h | 14 +++++++++++---
>  1 file changed, 11 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/filter.h b/include/linux/filter.h
> index bbce89937fde..1f237a3bb11a 100644
> --- a/include/linux/filter.h
> +++ b/include/linux/filter.h
> @@ -923,13 +923,21 @@ bool bpf_jit_supports_kfunc_call(void);
>  bool bpf_jit_supports_far_kfunc_call(void);
>  bool bpf_helper_changes_pkt_data(void *func);
>
> +/*
> + * Reconstruction of call-sites is dependent on kallsyms,
> + * thus make dump the same restriction.
> + */
> +#ifdef CONFIG_KALLSYMS
>  static inline bool bpf_dump_raw_ok(const struct cred *cred)
>  {
> -       /* Reconstruction of call-sites is dependent on kallsyms,
> -        * thus make dump the same restriction.
> -        */
>         return kallsyms_show_value(cred);
>  }
> +#else
> +static inline bool bpf_dump_raw_ok(const struct cred *cred)
> +{
> +       return false;
> +}
> +#endif
>
>  struct bpf_prog *bpf_patch_insn_single(struct bpf_prog *prog, u32 off,
>                                        const struct bpf_insn *patch, u32 len);
> --
> 2.17.1
>