[RFC bpf-next v2 3/9] bpf: attach a module BTF to a bpf_struct_ops

[thinker.li@gmail.com]

From: Kui-Feng Lee <thinker.li@gmail.com>

Every struct_ops type should has an associated module BTF to provide type
information since we are going to allow modules to define and register new
struct_ops types. New types may exist only in module itself, and the kernel
BTF (vmlinux) doesn't know it at all. The attached module BTF here will be
used to resolve type IDs of a struct_ops map.
---
 include/linux/bpf.h         |  5 +++--
 kernel/bpf/bpf_struct_ops.c | 34 +++++++++++++++++++++++-----------
 kernel/bpf/verifier.c       |  2 +-
 3 files changed, 27 insertions(+), 14 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 10f98f0ddc77..a9369f982cd5 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1614,6 +1614,7 @@ struct bpf_struct_ops {
 	void (*unreg)(void *kdata);
 	int (*update)(void *kdata, void *old_kdata);
 	int (*validate)(void *kdata);
+	const struct btf *btf;
 	const struct btf_type *type;
 	const struct btf_type *value_type;
 	const char *name;
@@ -1629,7 +1630,7 @@ struct bpf_struct_ops_mod {
 
 #if defined(CONFIG_BPF_JIT) && defined(CONFIG_BPF_SYSCALL)
 #define BPF_MODULE_OWNER ((void *)((0xeB9FUL << 2) + POISON_POINTER_DELTA))
-const struct bpf_struct_ops *bpf_struct_ops_find(u32 type_id);
+const struct bpf_struct_ops *bpf_struct_ops_find(u32 type_id, struct btf *btf);
 void bpf_struct_ops_init(struct btf *btf, struct bpf_verifier_log *log);
 bool bpf_struct_ops_get(const void *kdata);
 void bpf_struct_ops_put(const void *kdata);
@@ -1672,7 +1673,7 @@ int bpf_struct_ops_test_run(struct bpf_prog *prog, const union bpf_attr *kattr,
 			    union bpf_attr __user *uattr);
 #endif
 #else
-static inline const struct bpf_struct_ops *bpf_struct_ops_find(u32 type_id)
+static inline const struct bpf_struct_ops *bpf_struct_ops_find(u32 type_id, struct btf *btf)
 {
 	return NULL;
 }
diff --git a/kernel/bpf/bpf_struct_ops.c b/kernel/bpf/bpf_struct_ops.c
index 9be6e07ccba5..82cc3f0638fa 100644
--- a/kernel/bpf/bpf_struct_ops.c
+++ b/kernel/bpf/bpf_struct_ops.c
@@ -188,6 +188,10 @@ static void bpf_struct_ops_init_one(struct bpf_struct_ops *st_ops,
 			pr_warn("Error in init bpf_struct_ops %s\n",
 				st_ops->name);
 		} else {
+			/* XXX: We need a owner (module) here to company
+			 * with type_id and value_id.
+			 */
+			st_ops->btf = btf;
 			st_ops->type_id = type_id;
 			st_ops->type = t;
 			st_ops->value_id = value_id;
@@ -328,7 +332,7 @@ EXPORT_SYMBOL(unregister_bpf_struct_ops);
 extern struct btf *btf_vmlinux;
 
 static const struct bpf_struct_ops *
-bpf_struct_ops_find_value(u32 value_id)
+bpf_struct_ops_find_value(u32 value_id, struct btf *btf)
 {
 	unsigned int i;
 
@@ -336,14 +340,15 @@ bpf_struct_ops_find_value(u32 value_id)
 		return NULL;
 
 	for (i = 0; i < bpf_struct_ops_num; i++) {
-		if (bpf_struct_ops[i]->value_id == value_id)
+		if (bpf_struct_ops[i]->value_id == value_id &&
+		    bpf_struct_ops[i]->btf == btf)
 			return bpf_struct_ops[i];
 	}
 
 	return NULL;
 }
 
-const struct bpf_struct_ops *bpf_struct_ops_find(u32 type_id)
+const struct bpf_struct_ops *bpf_struct_ops_find(u32 type_id, struct btf *btf)
 {
 	unsigned int i;
 
@@ -351,7 +356,8 @@ const struct bpf_struct_ops *bpf_struct_ops_find(u32 type_id)
 		return NULL;
 
 	for (i = 0; i < bpf_struct_ops_num; i++) {
-		if (bpf_struct_ops[i]->type_id == type_id)
+		if (bpf_struct_ops[i]->type_id == type_id &&
+		    bpf_struct_ops[i]->btf == btf)
 			return bpf_struct_ops[i];
 	}
 
@@ -423,7 +429,7 @@ static void bpf_struct_ops_map_put_progs(struct bpf_struct_ops_map *st_map)
 	}
 }
 
-static int check_zero_holes(const struct btf_type *t, void *data)
+static int check_zero_holes(const struct btf *btf, const struct btf_type *t, void *data)
 {
 	const struct btf_member *member;
 	u32 i, moff, msize, prev_mend = 0;
@@ -435,8 +441,8 @@ static int check_zero_holes(const struct btf_type *t, void *data)
 		    memchr_inv(data + prev_mend, 0, moff - prev_mend))
 			return -EINVAL;
 
-		mtype = btf_type_by_id(btf_vmlinux, member->type);
-		mtype = btf_resolve_size(btf_vmlinux, mtype, &msize);
+		mtype = btf_type_by_id(btf, member->type);
+		mtype = btf_resolve_size(btf, mtype, &msize);
 		if (IS_ERR(mtype))
 			return PTR_ERR(mtype);
 		prev_mend = moff + msize;
@@ -489,7 +495,7 @@ static long bpf_struct_ops_map_update_elem(struct bpf_map *map, void *key,
 	const struct bpf_struct_ops *st_ops = st_map->st_ops;
 	struct bpf_struct_ops_value *uvalue, *kvalue;
 	const struct btf_member *member;
-	const struct btf_type *t = st_ops->type;
+	const struct btf_type *t;
 	struct bpf_tramp_links *tlinks;
 	void *udata, *kdata;
 	int prog_fd, err;
@@ -499,15 +505,20 @@ static long bpf_struct_ops_map_update_elem(struct bpf_map *map, void *key,
 	if (flags)
 		return -EINVAL;
 
+	if (!st_ops)
+		return -EINVAL;
+
+	t = st_ops->type;
+
 	if (*(u32 *)key != 0)
 		return -E2BIG;
 
-	err = check_zero_holes(st_ops->value_type, value);
+	err = check_zero_holes(st_ops->btf, st_ops->value_type, value);
 	if (err)
 		return err;
 
 	uvalue = value;
-	err = check_zero_holes(t, uvalue->data);
+	err = check_zero_holes(st_ops->btf, t, uvalue->data);
 	if (err)
 		return err;
 
@@ -773,8 +784,9 @@ static struct bpf_map *bpf_struct_ops_map_alloc(union bpf_attr *attr)
 	struct bpf_struct_ops_map *st_map;
 	const struct btf_type *t, *vt;
 	struct bpf_map *map;
+	struct btf *btf;
 
-	st_ops = bpf_struct_ops_find_value(attr->btf_vmlinux_value_type_id);
+	st_ops = bpf_struct_ops_find_value(attr->btf_vmlinux_value_type_id, btf_vmlinux);
 	if (!st_ops)
 		return ERR_PTR(-ENOTSUPP);
 
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index bb78212fa5b2..c0cab601b2a6 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -19191,7 +19191,7 @@ static int check_struct_ops_btf_id(struct bpf_verifier_env *env)
 	}
 
 	btf_id = prog->aux->attach_btf_id;
-	st_ops = bpf_struct_ops_find(btf_id);
+	st_ops = bpf_struct_ops_find(btf_id, btf_vmlinux);
 	if (!st_ops) {
 		verbose(env, "attach_btf_id %u is not a supported struct\n",
 			btf_id);
-- 
2.34.1