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,
> + 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
>
