bpf: Introduce internal definitions for UAPI-opaque bpf_{rb,list}_node

Structs bpf_rb_node and bpf_list_node are opaquely defined in
uapi/linux/bpf.h, as BPF program writers are not expected to touch their
fields - nor does the verifier allow them to do so.

Currently these structs are simple wrappers around structs rb_node and
list_head and linked_list / rbtree implementation just casts and passes
to library functions for those data structures. Later patches in this
series, though, will add an "owner" field to bpf_{rb,list}_node, such
that they're not just wrapping an underlying node type. Moreover, the
bpf linked_list and rbtree implementations will deal with these owner
pointers directly in a few different places.

To avoid having to do

  void *owner = (void*)bpf_list_node + sizeof(struct list_head)

with opaque UAPI node types, add bpf_{list,rb}_node_kern struct
definitions to internal headers and modify linked_list and rbtree to use
the internal types where appropriate.

Signed-off-by: Dave Marchevsky <davemarchevsky@fb.com>
Link: https://lore.kernel.org/r/20230718083813.3416104-3-davemarchevsky@fb.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

include/linux/bpf.h

@@ -228,6 +228,16 @@ struct btf_record {
 	struct btf_field fields[];
 };
 
+/* Non-opaque version of bpf_rb_node in uapi/linux/bpf.h */
+struct bpf_rb_node_kern {
+	struct rb_node rb_node;
+} __attribute__((aligned(8)));
+
+/* Non-opaque version of bpf_list_node in uapi/linux/bpf.h */
+struct bpf_list_node_kern {
+	struct list_head list_head;
+} __attribute__((aligned(8)));
+
 struct bpf_map {
 	/* The first two cachelines with read-mostly members of which some
 	 * are also accessed in fast-path (e.g. ops, max_entries).

kernel/bpf/helpers.c

@@ -1942,10 +1942,11 @@ __bpf_kfunc void *bpf_refcount_acquire_impl(void *p__refcounted_kptr, void *meta
 	return (void *)p__refcounted_kptr;
 }
 
-static int __bpf_list_add(struct bpf_list_node *node, struct bpf_list_head *head,
+static int __bpf_list_add(struct bpf_list_node_kern *node,
+			  struct bpf_list_head *head,
 			  bool tail, struct btf_record *rec, u64 off)
 {
-	struct list_head *n = (void *)node, *h = (void *)head;
+	struct list_head *n = &node->list_head, *h = (void *)head;
 
 	/* If list_head was 0-initialized by map, bpf_obj_init_field wasn't
 	 * called on its fields, so init here
@@ -1967,20 +1968,20 @@ __bpf_kfunc int bpf_list_push_front_impl(struct bpf_list_head *head,
 					 struct bpf_list_node *node,
 					 void *meta__ign, u64 off)
 {
+	struct bpf_list_node_kern *n = (void *)node;
 	struct btf_struct_meta *meta = meta__ign;
 
-	return __bpf_list_add(node, head, false,
-			      meta ? meta->record : NULL, off);
+	return __bpf_list_add(n, head, false, meta ? meta->record : NULL, off);
 }
 
 __bpf_kfunc int bpf_list_push_back_impl(struct bpf_list_head *head,
 					struct bpf_list_node *node,
 					void *meta__ign, u64 off)
 {
+	struct bpf_list_node_kern *n = (void *)node;
 	struct btf_struct_meta *meta = meta__ign;
 
-	return __bpf_list_add(node, head, true,
-			      meta ? meta->record : NULL, off);
+	return __bpf_list_add(n, head, true, meta ? meta->record : NULL, off);
 }
 
 static struct bpf_list_node *__bpf_list_del(struct bpf_list_head *head, bool tail)
@@ -2013,7 +2014,7 @@ __bpf_kfunc struct bpf_rb_node *bpf_rbtree_remove(struct bpf_rb_root *root,
 						  struct bpf_rb_node *node)
 {
 	struct rb_root_cached *r = (struct rb_root_cached *)root;
-	struct rb_node *n = (struct rb_node *)node;
+	struct rb_node *n = &((struct bpf_rb_node_kern *)node)->rb_node;
 
 	if (RB_EMPTY_NODE(n))
 		return NULL;
@@ -2026,11 +2027,12 @@ __bpf_kfunc struct bpf_rb_node *bpf_rbtree_remove(struct bpf_rb_root *root,
 /* Need to copy rbtree_add_cached's logic here because our 'less' is a BPF
  * program
  */
-static int __bpf_rbtree_add(struct bpf_rb_root *root, struct bpf_rb_node *node,
+static int __bpf_rbtree_add(struct bpf_rb_root *root,
+			    struct bpf_rb_node_kern *node,
 			    void *less, struct btf_record *rec, u64 off)
 {
 	struct rb_node **link = &((struct rb_root_cached *)root)->rb_root.rb_node;
-	struct rb_node *parent = NULL, *n = (struct rb_node *)node;
+	struct rb_node *parent = NULL, *n = &node->rb_node;
 	bpf_callback_t cb = (bpf_callback_t)less;
 	bool leftmost = true;
 
@@ -2060,8 +2062,9 @@ __bpf_kfunc int bpf_rbtree_add_impl(struct bpf_rb_root *root, struct bpf_rb_node
 				    void *meta__ign, u64 off)
 {
 	struct btf_struct_meta *meta = meta__ign;
+	struct bpf_rb_node_kern *n = (void *)node;
 
-	return __bpf_rbtree_add(root, node, (void *)less, meta ? meta->record : NULL, off);
+	return __bpf_rbtree_add(root, n, (void *)less, meta ? meta->record : NULL, off);
 }
 
 __bpf_kfunc struct bpf_rb_node *bpf_rbtree_first(struct bpf_rb_root *root)