[External] Re: [PATCH bpf-next v2 5/9] bpf: verifier: add btf to the function args of bpf_check_attach_target

[梦龙董]

On Tue, Mar 12, 2024 at 9:51 AM Alexei Starovoitov
<alexei.starovoitov at gmail.com> wrote:
>
> On Mon, Mar 11, 2024 at 2:35 AM Menglong Dong
> <dongmenglong.8 at bytedance.com> wrote:
> >
> > Add target btf to the function args of bpf_check_attach_target(), then
> > the caller can specify the btf to check.
> >
> > Signed-off-by: Menglong Dong <dongmenglong.8 at bytedance.com>
> > ---
> >  include/linux/bpf_verifier.h | 1 +
> >  kernel/bpf/syscall.c         | 6 ++++--
> >  kernel/bpf/trampoline.c      | 1 +
> >  kernel/bpf/verifier.c        | 8 +++++---
> >  4 files changed, 11 insertions(+), 5 deletions(-)
> >
> > diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
> > index 4b0f6600e499..6cb20efcfac3 100644
> > --- a/include/linux/bpf_verifier.h
> > +++ b/include/linux/bpf_verifier.h
> > @@ -811,6 +811,7 @@ static inline void bpf_trampoline_unpack_key(u64 key, u32 *obj_id, u32 *btf_id)
> >  int bpf_check_attach_target(struct bpf_verifier_log *log,
> >                             const struct bpf_prog *prog,
> >                             const struct bpf_prog *tgt_prog,
> > +                           struct btf *btf,
> >                             u32 btf_id,
> >                             struct bpf_attach_target_info *tgt_info);
> >  void bpf_free_kfunc_btf_tab(struct bpf_kfunc_btf_tab *tab);
> > diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> > index d1cd645ef9ac..6128c3131141 100644
> > --- a/kernel/bpf/syscall.c
> > +++ b/kernel/bpf/syscall.c
> > @@ -3401,9 +3401,11 @@ static int bpf_tracing_prog_attach(struct bpf_prog *prog,
> >                  * need a new trampoline and a check for compatibility
> >                  */
> >                 struct bpf_attach_target_info tgt_info = {};
> > +               struct btf *btf;
> >
> > -               err = bpf_check_attach_target(NULL, prog, tgt_prog, btf_id,
> > -                                             &tgt_info);
> > +               btf = tgt_prog ? tgt_prog->aux->btf : prog->aux->attach_btf;
>
> I think it's better to keep this bit inside bpf_check_attach_target(),
> since a lot of other code in there is working with if (tgt_prog) ...
> so if the caller messes up passing tgt_prog->aux->btf with tgt_prog
> the bug will be difficult to debug.

In the previous version, I pass the attach_btf with the following
way:

+            origin_btf = prog->aux->attach_btf;
+             /* use the new attach_btf to check the target */
+             prog->aux->attach_btf = attach_btf;
              err = bpf_check_attach_target(NULL, prog, tgt_prog, btf_id,
                                            &tgt_info);
+             prog->aux->attach_btf = origin_btf;

And Jiri suggested to add the attach_btf to the function args
of bpf_check_attach_target().

Ennn....Should I convert to the old way?

Thanks!
Menglong Dong

>
> > +               err = bpf_check_attach_target(NULL, prog, tgt_prog, btf,
> > +                                             btf_id, &tgt_info);