[RFC,bpf-next,v2,1/9] bpf: add a get_helper_proto() utility function

Commit Message

Eduard Zingerman July 4, 2024, 10:23 a.m. UTC

Extract the part of check_helper_call() as a utility function allowing
to query 'struct bpf_func_proto' for a specific helper function id.

Signed-off-by: Eduard Zingerman <[e-mail]>
---
 kernel/bpf/verifier.c | 30 +++++++++++++++++++++++-------
 1 file changed, 23 insertions(+), 7 deletions(-)

Comments

Andrii Nakryiko July 9, 2024, 11:42 p.m. UTC | #1

On Thu, Jul 4, 2024 at 3:24 AM Eduard Zingerman <[e-mail]> wrote:
>
> Extract the part of check_helper_call() as a utility function allowing
> to query 'struct bpf_func_proto' for a specific helper function id.
>
> Signed-off-by: Eduard Zingerman <[e-mail]>
> ---
>  kernel/bpf/verifier.c | 30 +++++++++++++++++++++++-------
>  1 file changed, 23 insertions(+), 7 deletions(-)
>

I'd write it differently (see below), but it's correct, so:

Acked-by: Andrii Nakryiko <[e-mail]>

> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index d3927d819465..4869f1fb0a42 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -10261,6 +10261,24 @@ static void update_loop_inline_state(struct bpf_verifier_env *env, u32 subprogno
>                                  state->callback_subprogno == subprogno);
>  }
>
> +static int get_helper_proto(struct bpf_verifier_env *env, int func_id,
> +                           const struct bpf_func_proto **ptr)
> +{
> +       const struct bpf_func_proto *result = NULL;
> +
> +       if (func_id < 0 || func_id >= __BPF_FUNC_MAX_ID)
> +               return -ERANGE;
> +
> +       if (env->ops->get_func_proto)
> +               result = env->ops->get_func_proto(func_id, env->prog);
> +
> +       if (!result)
> +               return -EINVAL;

result is a bit unnecessary. We could do either

*ptr = NULL;
if (env->ops->get_func_proto)
    *ptr = env->ops->get_func_proto(func_id, env->prog);
return *ptr ? 0 : -EINVAL;


or just

if (!env->ops->get_func_proto)
    return -EINVAL;

*ptr = env->ops->get_func_proto(func_id, env->prog);

return *ptr ? 0 : -EINVAL;


> +
> +       *ptr = result;
> +       return 0;
> +}
> +
>  static int check_helper_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
>                              int *insn_idx_p)
>  {
> @@ -10277,18 +10295,16 @@ static int check_helper_call(struct bpf_verifier_env *env, struct bpf_insn *insn
>
>         /* find function prototype */
>         func_id = insn->imm;
> -       if (func_id < 0 || func_id >= __BPF_FUNC_MAX_ID) {
> -               verbose(env, "invalid func %s#%d\n", func_id_name(func_id),
> -                       func_id);
> +       err = get_helper_proto(env, insn->imm, &fn);
> +       if (err == -ERANGE) {
> +               verbose(env, "invalid func %s#%d\n", func_id_name(func_id), func_id);
>                 return -EINVAL;
>         }
>
> -       if (env->ops->get_func_proto)
> -               fn = env->ops->get_func_proto(func_id, env->prog);
> -       if (!fn) {
> +       if (err) {

nit: this is one block of error handling, I'd keep it "connected":

if (err == -ERANGE) {
} else if (err) {

}


>                 verbose(env, "program of this type cannot use helper %s#%d\n",
>                         func_id_name(func_id), func_id);
> -               return -EINVAL;
> +               return err;
>         }
>
>         /* eBPF programs must be GPL compatible to use GPL-ed functions */
> --
> 2.45.2
>

Eduard Zingerman July 10, 2024, 12:26 a.m. UTC | #2

On Tue, 2024-07-09 at 16:42 -0700, Andrii Nakryiko wrote:

[...]

> > @@ -10261,6 +10261,24 @@ static void update_loop_inline_state(struct bpf_verifier_env *env, u32 subprogno
> >                                  state->callback_subprogno == subprogno);
> >  }
> > 
> > +static int get_helper_proto(struct bpf_verifier_env *env, int func_id,
> > +                           const struct bpf_func_proto **ptr)
> > +{
> > +       const struct bpf_func_proto *result = NULL;
> > +
> > +       if (func_id < 0 || func_id >= __BPF_FUNC_MAX_ID)
> > +               return -ERANGE;
> > +
> > +       if (env->ops->get_func_proto)
> > +               result = env->ops->get_func_proto(func_id, env->prog);
> > +
> > +       if (!result)
> > +               return -EINVAL;
> 
> result is a bit unnecessary. We could do either
> 
> *ptr = NULL;
> if (env->ops->get_func_proto)
>     *ptr = env->ops->get_func_proto(func_id, env->prog);
> return *ptr ? 0 : -EINVAL;
> 
> 
> or just
> 
> if (!env->ops->get_func_proto)
>     return -EINVAL;
> 
> *ptr = env->ops->get_func_proto(func_id, env->prog);
> 
> return *ptr ? 0 : -EINVAL;

Ok, will change in v3.

[...]

Patch

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index d3927d819465..4869f1fb0a42 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -10261,6 +10261,24 @@  static void update_loop_inline_state(struct bpf_verifier_env *env, u32 subprogno
 				 state->callback_subprogno == subprogno);
 }
 
+static int get_helper_proto(struct bpf_verifier_env *env, int func_id,
+			    const struct bpf_func_proto **ptr)
+{
+	const struct bpf_func_proto *result = NULL;
+
+	if (func_id < 0 || func_id >= __BPF_FUNC_MAX_ID)
+		return -ERANGE;
+
+	if (env->ops->get_func_proto)
+		result = env->ops->get_func_proto(func_id, env->prog);
+
+	if (!result)
+		return -EINVAL;
+
+	*ptr = result;
+	return 0;
+}
+
 static int check_helper_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
 			     int *insn_idx_p)
 {
@@ -10277,18 +10295,16 @@  static int check_helper_call(struct bpf_verifier_env *env, struct bpf_insn *insn
 
 	/* find function prototype */
 	func_id = insn->imm;
-	if (func_id < 0 || func_id >= __BPF_FUNC_MAX_ID) {
-		verbose(env, "invalid func %s#%d\n", func_id_name(func_id),
-			func_id);
+	err = get_helper_proto(env, insn->imm, &fn);
+	if (err == -ERANGE) {
+		verbose(env, "invalid func %s#%d\n", func_id_name(func_id), func_id);
 		return -EINVAL;
 	}
 
-	if (env->ops->get_func_proto)
-		fn = env->ops->get_func_proto(func_id, env->prog);
-	if (!fn) {
+	if (err) {
 		verbose(env, "program of this type cannot use helper %s#%d\n",
 			func_id_name(func_id), func_id);
-		return -EINVAL;
+		return err;
 	}
 
 	/* eBPF programs must be GPL compatible to use GPL-ed functions */