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From: Andrii Nakryiko <andrii.nakryiko@gmail.com>
To: Yonghong Song <yhs@fb.com>
Cc: bpf <bpf@vger.kernel.org>, Alexei Starovoitov <ast@kernel.org>,
	Cong Wang <xiyou.wangcong@gmail.com>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Kernel Team <kernel-team@fb.com>
Subject: Re: [PATCH bpf-next v3 03/11] bpf: refactor check_func_call() to allow callback function
Date: Thu, 25 Feb 2021 14:31:47 -0800	[thread overview]
Message-ID: <CAEf4BzbdNTc4wqnhPPhfQeO0rARMHNocZ28xgR6cY1OVDAti1w@mail.gmail.com> (raw)
In-Reply-To: <CAEf4BzZn125xN0p=mUvAfFzq+Pbequm9Yp0rSN0B=ru4X8X8Jg@mail.gmail.com>

On Thu, Feb 25, 2021 at 2:05 PM Andrii Nakryiko
<andrii.nakryiko@gmail.com> wrote:
>
> On Thu, Feb 25, 2021 at 1:35 AM Yonghong Song <yhs@fb.com> wrote:
> >
> > Later proposed bpf_for_each_map_elem() helper has callback
> > function as one of its arguments. This patch refactored
> > check_func_call() to permit callback function which sets
> > callee state. Different callback functions may have
> > different callee states.
> >
> > There is no functionality change for this patch except
> > it added a case to handle where subprog number is known
> > and there is no need to do find_subprog(). This case
> > is used later by implementing bpf_for_each_map() helper.
> >
> > Signed-off-by: Yonghong Song <yhs@fb.com>
> > ---
> >  kernel/bpf/verifier.c | 54 ++++++++++++++++++++++++++++++++-----------
> >  1 file changed, 41 insertions(+), 13 deletions(-)
> >
> > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> > index a657860ecba5..092d2c734dd8 100644
> > --- a/kernel/bpf/verifier.c
> > +++ b/kernel/bpf/verifier.c
> > @@ -5250,13 +5250,19 @@ static void clear_caller_saved_regs(struct bpf_verifier_env *env,
> >         }
> >  }
> >
> > -static int check_func_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
> > -                          int *insn_idx)
> > +typedef int (*set_callee_state_fn)(struct bpf_verifier_env *env,
> > +                                  struct bpf_func_state *caller,
> > +                                  struct bpf_func_state *callee,
> > +                                  int insn_idx);
> > +
> > +static int __check_func_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
> > +                            int *insn_idx, int subprog,

ok, patch #4 confused me because of this `int *insn_idx`. You don't
seem to be ever updating it, so why pass it by pointer?... What did I
miss?

> > +                            set_callee_state_fn set_callee_st)
>
> nit: s/set_callee_st/set_callee_state_cb|set_calle_state_fn/
>
> _st is quite an unusual suffix
>
> >  {
> >         struct bpf_verifier_state *state = env->cur_state;
> >         struct bpf_func_info_aux *func_info_aux;
> >         struct bpf_func_state *caller, *callee;
> > -       int i, err, subprog, target_insn;
> > +       int err, target_insn;
> >         bool is_global = false;
> >
> >         if (state->curframe + 1 >= MAX_CALL_FRAMES) {
> > @@ -5265,12 +5271,16 @@ static int check_func_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
> >                 return -E2BIG;
> >         }
> >
> > -       target_insn = *insn_idx + insn->imm;
> > -       subprog = find_subprog(env, target_insn + 1);
> >         if (subprog < 0) {
> > -               verbose(env, "verifier bug. No program starts at insn %d\n",
> > -                       target_insn + 1);
> > -               return -EFAULT;
> > +               target_insn = *insn_idx + insn->imm;
> > +               subprog = find_subprog(env, target_insn + 1);
> > +               if (subprog < 0) {
> > +                       verbose(env, "verifier bug. No program starts at insn %d\n",
> > +                               target_insn + 1);
> > +                       return -EFAULT;
> > +               }
> > +       } else {
> > +               target_insn = env->subprog_info[subprog].start - 1;
> >         }
> >
> >         caller = state->frame[state->curframe];
> > @@ -5327,11 +5337,9 @@ static int check_func_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
> >         if (err)
> >                 return err;
> >
> > -       /* copy r1 - r5 args that callee can access.  The copy includes parent
> > -        * pointers, which connects us up to the liveness chain
> > -        */
> > -       for (i = BPF_REG_1; i <= BPF_REG_5; i++)
> > -               callee->regs[i] = caller->regs[i];
> > +       err = set_callee_st(env, caller, callee, *insn_idx);
> > +       if (err)
> > +               return err;
> >
> >         clear_caller_saved_regs(env, caller->regs);
> >
> > @@ -5350,6 +5358,26 @@ static int check_func_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
> >         return 0;
> >  }
> >
> > +static int set_callee_state(struct bpf_verifier_env *env,
> > +                           struct bpf_func_state *caller,
> > +                           struct bpf_func_state *callee, int insn_idx)
> > +{
> > +       int i;
> > +
> > +       /* copy r1 - r5 args that callee can access.  The copy includes parent
> > +        * pointers, which connects us up to the liveness chain
> > +        */
> > +       for (i = BPF_REG_1; i <= BPF_REG_5; i++)
> > +               callee->regs[i] = caller->regs[i];
> > +       return 0;
> > +}
> > +
> > +static int check_func_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
> > +                          int *insn_idx)
> > +{
> > +       return __check_func_call(env, insn, insn_idx, -1, set_callee_state);
>
> I think it would be much cleaner to not have this -1 special case in
> __check_func_call and instead search for the right subprog right here
> in check_func_call(). Related question, is meta.subprogno (in patch
> #4) expected to sometimes be < 0? If not, then I think
> __check_func_call() definitely shouldn't support -1 case at all.
>
>
> > +}
> > +
> >  static int prepare_func_exit(struct bpf_verifier_env *env, int *insn_idx)
> >  {
> >         struct bpf_verifier_state *state = env->cur_state;
> > --
> > 2.24.1
> >

  reply	other threads:[~2021-02-25 22:32 UTC|newest]

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-02-25  7:33 [PATCH bpf-next v3 00/11] bpf: add bpf_for_each_map_elem() helper Yonghong Song
2021-02-25  7:33 ` [PATCH bpf-next v3 01/11] bpf: factor out visit_func_call_insn() in check_cfg() Yonghong Song
2021-02-25 21:54   ` Andrii Nakryiko
2021-02-25 22:01     ` Alexei Starovoitov
2021-02-25  7:33 ` [PATCH bpf-next v3 02/11] bpf: factor out verbose_invalid_scalar() Yonghong Song
2021-02-25 21:56   ` Andrii Nakryiko
2021-02-25  7:33 ` [PATCH bpf-next v3 03/11] bpf: refactor check_func_call() to allow callback function Yonghong Song
2021-02-25 22:05   ` Andrii Nakryiko
2021-02-25 22:31     ` Andrii Nakryiko [this message]
2021-02-26  0:08       ` Yonghong Song
2021-02-26  1:18         ` Andrii Nakryiko
2021-02-26  0:05     ` Yonghong Song
2021-02-25  7:33 ` [PATCH bpf-next v3 04/11] bpf: add bpf_for_each_map_elem() helper Yonghong Song
2021-02-25 22:41   ` Andrii Nakryiko
2021-02-26  2:16     ` Yonghong Song
2021-02-26  3:22       ` Yonghong Song
2021-02-26  2:27   ` Cong Wang
2021-02-26  3:27     ` Yonghong Song
2021-02-25  7:33 ` [PATCH bpf-next v3 05/11] bpf: add hashtab support for " Yonghong Song
2021-02-25 22:44   ` Andrii Nakryiko
2021-02-25  7:33 ` [PATCH bpf-next v3 06/11] bpf: add arraymap " Yonghong Song
2021-02-25 22:48   ` Andrii Nakryiko
2021-02-25  7:33 ` [PATCH bpf-next v3 07/11] libbpf: move function is_ldimm64() earlier in libbpf.c Yonghong Song
2021-02-25  7:33 ` [PATCH bpf-next v3 08/11] libbpf: support subprog address relocation Yonghong Song
2021-02-25 23:04   ` Andrii Nakryiko
2021-02-25  7:33 ` [PATCH bpf-next v3 09/11] bpftool: print subprog address properly Yonghong Song
2021-02-25 23:04   ` Andrii Nakryiko
2021-02-25  7:33 ` [PATCH bpf-next v3 10/11] selftests/bpf: add hashmap test for bpf_for_each_map_elem() helper Yonghong Song
2021-02-25 23:25   ` Andrii Nakryiko
2021-02-26  3:24     ` Yonghong Song
2021-02-25  7:33 ` [PATCH bpf-next v3 11/11] selftests/bpf: add arraymap " Yonghong Song
2021-02-25 23:26   ` Andrii Nakryiko

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