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From: =?UTF-8?B?5qKm6b6Z6JGj?= <dongmenglong.8@bytedance.com>
Date: Tue, 12 Mar 2024 11:13:50 +0800
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Subject: Re: [External] Re: [PATCH bpf-next v2 5/9] bpf: verifier: add btf to
 the function args of bpf_check_attach_target
To: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: Andrii Nakryiko <andrii@kernel.org>, Alexei Starovoitov <ast@kernel.org>, 
	Daniel Borkmann <daniel@iogearbox.net>, Martin KaFai Lau <martin.lau@linux.dev>, Eddy Z <eddyz87@gmail.com>, 
	Song Liu <song@kernel.org>, Yonghong Song <yonghong.song@linux.dev>, 
	John Fastabend <john.fastabend@gmail.com>, KP Singh <kpsingh@kernel.org>, 
	Stanislav Fomichev <sdf@google.com>, Hao Luo <haoluo@google.com>, Jiri Olsa <jolsa@kernel.org>, 
	Alexander Gordeev <agordeev@linux.ibm.com>, Christian Borntraeger <borntraeger@linux.ibm.com>, 
	Sven Schnelle <svens@linux.ibm.com>, "David S. Miller" <davem@davemloft.net>, 
	David Ahern <dsahern@kernel.org>, Dave Hansen <dave.hansen@linux.intel.com>, 
	X86 ML <x86@kernel.org>, Steven Rostedt <rostedt@goodmis.org>, 
	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>, Quentin Monnet <quentin@isovalent.com>, 
	bpf <bpf@vger.kernel.org>, 
	linux-arm-kernel <linux-arm-kernel@lists.infradead.org>, LKML <linux-kernel@vger.kernel.org>, 
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	Network Development <netdev@vger.kernel.org>, linux-trace-kernel@vger.kernel.org, 
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On Tue, Mar 12, 2024 at 9:51=E2=80=AFAM Alexei Starovoitov
<alexei.starovoitov@gmail.com> wrote:
>
> On Mon, Mar 11, 2024 at 2:35=E2=80=AFAM 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 ke=
y, 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_pr=
og *prog,
> >                  * need a new trampoline and a check for compatibility
> >                  */
> >                 struct bpf_attach_target_info tgt_info =3D {};
> > +               struct btf *btf;
> >
> > -               err =3D bpf_check_attach_target(NULL, prog, tgt_prog, b=
tf_id,
> > -                                             &tgt_info);
> > +               btf =3D tgt_prog ? tgt_prog->aux->btf : prog->aux->atta=
ch_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 =3D prog->aux->attach_btf;
+             /* use the new attach_btf to check the target */
+             prog->aux->attach_btf =3D attach_btf;
              err =3D bpf_check_attach_target(NULL, prog, tgt_prog, btf_id,
                                            &tgt_info);
+             prog->aux->attach_btf =3D 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 =3D bpf_check_attach_target(NULL, prog, tgt_prog, b=
tf,
> > +                                             btf_id, &tgt_info);