On Thu, Feb 25, 2021 at 2:05 PM Andrii Nakryiko
<andrii.nakryiko@xxxxxxxxx> wrote:
>
> On Thu, Feb 25, 2021 at 1:35 AM Yonghong Song <yhs@xxxxxx> 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@xxxxxx>
> > ---
> > 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
> >
