bpf: Rewrite kfunc argument handling

As we continue to add more features, argument types, kfunc flags, and
different extensions to kfuncs, the code to verify the correctness of
the kfunc prototype wrt the passed in registers has become ad-hoc and
ugly to read.

To make life easier, and make a very clear split between different
stages of argument processing, move all the code into verifier.c and
refactor into easier to read helpers and functions.

This also makes sharing code within the verifier easier with kfunc
argument processing. This will be more and more useful in later patches
as we are now moving to implement very core BPF helpers as kfuncs, to
keep them experimental before baking into UAPI.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>

include/linux/btf.h

@@ -339,6 +339,16 @@ static inline bool btf_type_is_struct(const struct btf_type *t)
 	return kind == BTF_KIND_STRUCT || kind == BTF_KIND_UNION;
 }
 
+static inline bool __btf_type_is_struct(const struct btf_type *t)
+{
+	return BTF_INFO_KIND(t->info) == BTF_KIND_STRUCT;
+}
+
+static inline bool btf_type_is_array(const struct btf_type *t)
+{
+	return BTF_INFO_KIND(t->info) == BTF_KIND_ARRAY;
+}
+
 static inline u16 btf_type_vlen(const struct btf_type *t)
 {
 	return BTF_INFO_VLEN(t->info);
@@ -442,6 +452,7 @@ static inline void *btf_id_set8_contains(const struct btf_id_set8 *set, u32 id)
 
 #ifdef CONFIG_BPF_SYSCALL
 struct bpf_prog;
+struct bpf_verifier_log;
 
 const struct btf_type *btf_type_by_id(const struct btf *btf, u32 type_id);
 const char *btf_name_by_offset(const struct btf *btf, u32 offset);
@@ -456,6 +467,12 @@ s32 btf_find_dtor_kfunc(struct btf *btf, u32 btf_id);
 int register_btf_id_dtor_kfuncs(const struct btf_id_dtor_kfunc *dtors, u32 add_cnt,
 				struct module *owner);
 struct btf_struct_meta *btf_find_struct_meta(const struct btf *btf, u32 btf_id);
+const struct btf_member *
+btf_get_prog_ctx_type(struct bpf_verifier_log *log, const struct btf *btf,
+		      const struct btf_type *t, enum bpf_prog_type prog_type,
+		      int arg);
+bool btf_types_are_same(const struct btf *btf1, u32 id1,
+			const struct btf *btf2, u32 id2);
 #else
 static inline const struct btf_type *btf_type_by_id(const struct btf *btf,
 						    u32 type_id)
@@ -491,6 +508,18 @@ static inline struct btf_struct_meta *btf_find_struct_meta(const struct btf *btf
 {
 	return NULL;
 }
+static inline const struct btf_member *
+btf_get_prog_ctx_type(struct bpf_verifier_log *log, const struct btf *btf,
+		      const struct btf_type *t, enum bpf_prog_type prog_type,
+		      int arg)
+{
+	return NULL;
+}
+static inline bool btf_types_are_same(const struct btf *btf1, u32 id1,
+				      const struct btf *btf2, u32 id2)
+{
+	return false;
+}
 #endif
 
 static inline bool btf_type_is_struct_ptr(struct btf *btf, const struct btf_type *t)

kernel/bpf/btf.c

@@ -478,16 +478,6 @@ static bool btf_type_nosize_or_null(const struct btf_type *t)
 	return !t || btf_type_nosize(t);
 }
 
-static bool __btf_type_is_struct(const struct btf_type *t)
-{
-	return BTF_INFO_KIND(t->info) == BTF_KIND_STRUCT;
-}
-
-static bool btf_type_is_array(const struct btf_type *t)
-{
-	return BTF_INFO_KIND(t->info) == BTF_KIND_ARRAY;
-}
-
 static bool btf_type_is_datasec(const struct btf_type *t)
 {
 	return BTF_INFO_KIND(t->info) == BTF_KIND_DATASEC;
@@ -5537,7 +5527,7 @@ static u8 bpf_ctx_convert_map[] = {
 #undef BPF_MAP_TYPE
 #undef BPF_LINK_TYPE
 
-static const struct btf_member *
+const struct btf_member *
 btf_get_prog_ctx_type(struct bpf_verifier_log *log, const struct btf *btf,
 		      const struct btf_type *t, enum bpf_prog_type prog_type,
 		      int arg)
@@ -6322,8 +6312,8 @@ int btf_struct_access(struct bpf_verifier_log *log,
  * end up with two different module BTFs, but IDs point to the common type in
  * vmlinux BTF.
  */
-static bool btf_types_are_same(const struct btf *btf1, u32 id1,
-			       const struct btf *btf2, u32 id2)
+bool btf_types_are_same(const struct btf *btf1, u32 id1,
+			const struct btf *btf2, u32 id2)
 {
 	if (id1 != id2)
 		return false;