bpf: Emit global subprog name in verifier logs

We have the name, instead of emitting just func#N to identify global
subprog, augment verifier log messages with actual function name to make
it more user-friendly.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20231124035937.403208-2-andrii@kernel.org

kernel/bpf/verifier.c

@@ -339,6 +339,11 @@ struct bpf_kfunc_call_arg_meta {
 
 struct btf *btf_vmlinux;
 
+static const char *btf_type_name(const struct btf *btf, u32 id)
+{
+	return btf_name_by_offset(btf, btf_type_by_id(btf, id)->name_off);
+}
+
 static DEFINE_MUTEX(bpf_verifier_lock);
 static DEFINE_MUTEX(bpf_percpu_ma_lock);
 
@@ -418,6 +423,17 @@ static bool subprog_is_global(const struct bpf_verifier_env *env, int subprog)
 	return aux && aux[subprog].linkage == BTF_FUNC_GLOBAL;
 }
 
+static const char *subprog_name(const struct bpf_verifier_env *env, int subprog)
+{
+	struct bpf_func_info *info;
+
+	if (!env->prog->aux->func_info)
+		return "";
+
+	info = &env->prog->aux->func_info[subprog];
+	return btf_type_name(env->prog->aux->btf, info->type_id);
+}
+
 static bool reg_may_point_to_spin_lock(const struct bpf_reg_state *reg)
 {
 	return btf_record_has_field(reg_btf_record(reg), BPF_SPIN_LOCK);
@@ -587,11 +603,6 @@ static int iter_get_spi(struct bpf_verifier_env *env, struct bpf_reg_state *reg,
 	return stack_slot_obj_get_spi(env, reg, "iter", nr_slots);
 }
 
-static const char *btf_type_name(const struct btf *btf, u32 id)
-{
-	return btf_name_by_offset(btf, btf_type_by_id(btf, id)->name_off);
-}
-
 static enum bpf_dynptr_type arg_to_dynptr_type(enum bpf_arg_type arg_type)
 {
 	switch (arg_type & DYNPTR_TYPE_FLAG_MASK) {
@@ -9269,13 +9280,16 @@ static int check_func_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
 	if (err == -EFAULT)
 		return err;
 	if (subprog_is_global(env, subprog)) {
+		const char *sub_name = subprog_name(env, subprog);
+
 		if (err) {
-			verbose(env, "Caller passes invalid args into func#%d\n", subprog);
+			verbose(env, "Caller passes invalid args into func#%d ('%s')\n",
+				subprog, sub_name);
 			return err;
 		}
 
-		if (env->log.level & BPF_LOG_LEVEL)
-			verbose(env, "Func#%d is global and valid. Skipping.\n", subprog);
+		verbose(env, "Func#%d ('%s') is global and assumed valid.\n",
+			subprog, sub_name);
 		clear_caller_saved_regs(env, caller->regs);
 
 		/* All global functions return a 64-bit SCALAR_VALUE */
@@ -19893,9 +19907,8 @@ static int do_check_subprogs(struct bpf_verifier_env *env)
 		if (ret) {
 			return ret;
 		} else if (env->log.level & BPF_LOG_LEVEL) {
-			verbose(env,
-				"Func#%d is safe for any args that match its prototype\n",
-				i);
+			verbose(env, "Func#%d ('%s') is safe for any args that match its prototype\n",
+				i, subprog_name(env, i));
 		}
 	}
 	return 0;