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

梦龙董
2024-03-12T03:14:02Z

On Tue, Mar 12, 2024 at 9:51 AM Alexei Starovoitov
<alexei.starovoitov@gmail.com> wrote:
>
> On Mon, Mar 11, 2024 at 2:35 AM Menglong Dong
> <dongmenglong.8@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@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);