Subject: [RFC PATCH bpf-next 08/12] bpf: Simplify reg0 marking for the list kfuncs that return a bpf_list_node pointer

From: Martin KaFai Lau <[email-masked]>
Date: Fri, 18 Apr 2025 15:46:46 -0700

From: Martin KaFai Lau <[email-masked]>

The next patch will add bpf_list_{front,back} kfuncs to peek the head
and tail of a list. Both of them will return a 'struct bpf_list_node *'.

Follow the earlier change for rbtree, this patch checks the
return btf type is a 'struct bpf_list_node' pointer instead
of checking each kfuncs individually to decide if
mark_reg_graph_node should be called. This will make
the bpf_list_{front,back} kfunc addition easier in
the later patch.

Signed-off-by: Martin KaFai Lau <[email-masked]>
---
 kernel/bpf/verifier.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 3b905331ca0e..aacde0274e0f 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -11992,6 +11992,11 @@ static bool is_rbtree_node_type(const struct btf_type *t)
 	return t == btf_type_by_id(btf_vmlinux, kf_arg_btf_ids[KF_ARG_RB_NODE_ID]);
 }
 
+static bool is_list_node_type(const struct btf_type *t)
+{
+	return t == btf_type_by_id(btf_vmlinux, kf_arg_btf_ids[KF_ARG_LIST_NODE_ID]);
+}
+
 static bool is_kfunc_arg_callback(struct bpf_verifier_env *env, const struct btf *btf,
 				  const struct btf_param *arg)
 {
@@ -13763,8 +13768,7 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
 				insn_aux->kptr_struct_meta =
 					btf_find_struct_meta(meta.arg_btf,
 							     meta.arg_btf_id);
-			} else if (meta.func_id == special_kfunc_list[KF_bpf_list_pop_front] ||
-				   meta.func_id == special_kfunc_list[KF_bpf_list_pop_back]) {
+			} else if (is_list_node_type(ptr_type)) {
 				struct btf_field *field = meta.arg_list_head.field;
 
 				mark_reg_graph_node(regs, BPF_REG_0, &field->graph_root);
-- 
2.47.1