bpf: Add basic bpf_rb_{root,node} support

This patch adds special BPF_RB_{ROOT,NODE} btf_field_types similar to
BPF_LIST_{HEAD,NODE}, adds the necessary plumbing to detect the new
types, and adds bpf_rb_root_free function for freeing bpf_rb_root in
map_values.

structs bpf_rb_root and bpf_rb_node are opaque types meant to
obscure structs rb_root_cached rb_node, respectively.

btf_struct_access will prevent BPF programs from touching these special
fields automatically now that they're recognized.

btf_check_and_fixup_fields now groups list_head and rb_root together as
"graph root" fields and {list,rb}_node as "graph node", and does same
ownership cycle checking as before. Note that this function does _not_
prevent ownership type mixups (e.g. rb_root owning list_node) - that's
handled by btf_parse_graph_root.

After this patch, a bpf program can have a struct bpf_rb_root in a
map_value, but not add anything to nor do anything useful with it.

Signed-off-by: Dave Marchevsky <davemarchevsky@fb.com>
Link: https://lore.kernel.org/r/20230214004017.2534011-2-davemarchevsky@fb.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

include/linux/bpf.h

@@ -181,7 +181,10 @@ enum btf_field_type {
 	BPF_KPTR       = BPF_KPTR_UNREF | BPF_KPTR_REF,
 	BPF_LIST_HEAD  = (1 << 4),
 	BPF_LIST_NODE  = (1 << 5),
-	BPF_GRAPH_NODE_OR_ROOT = BPF_LIST_NODE | BPF_LIST_HEAD,
+	BPF_RB_ROOT    = (1 << 6),
+	BPF_RB_NODE    = (1 << 7),
+	BPF_GRAPH_NODE_OR_ROOT = BPF_LIST_NODE | BPF_LIST_HEAD |
+				 BPF_RB_NODE | BPF_RB_ROOT,
 };
 
 struct btf_field_kptr {
@@ -285,6 +288,10 @@ static inline const char *btf_field_type_name(enum btf_field_type type)
 		return "bpf_list_head";
 	case BPF_LIST_NODE:
 		return "bpf_list_node";
+	case BPF_RB_ROOT:
+		return "bpf_rb_root";
+	case BPF_RB_NODE:
+		return "bpf_rb_node";
 	default:
 		WARN_ON_ONCE(1);
 		return "unknown";
@@ -305,6 +312,10 @@ static inline u32 btf_field_type_size(enum btf_field_type type)
 		return sizeof(struct bpf_list_head);
 	case BPF_LIST_NODE:
 		return sizeof(struct bpf_list_node);
+	case BPF_RB_ROOT:
+		return sizeof(struct bpf_rb_root);
+	case BPF_RB_NODE:
+		return sizeof(struct bpf_rb_node);
 	default:
 		WARN_ON_ONCE(1);
 		return 0;
@@ -325,6 +336,10 @@ static inline u32 btf_field_type_align(enum btf_field_type type)
 		return __alignof__(struct bpf_list_head);
 	case BPF_LIST_NODE:
 		return __alignof__(struct bpf_list_node);
+	case BPF_RB_ROOT:
+		return __alignof__(struct bpf_rb_root);
+	case BPF_RB_NODE:
+		return __alignof__(struct bpf_rb_node);
 	default:
 		WARN_ON_ONCE(1);
 		return 0;
@@ -435,6 +450,9 @@ void copy_map_value_locked(struct bpf_map *map, void *dst, void *src,
 void bpf_timer_cancel_and_free(void *timer);
 void bpf_list_head_free(const struct btf_field *field, void *list_head,
 			struct bpf_spin_lock *spin_lock);
+void bpf_rb_root_free(const struct btf_field *field, void *rb_root,
+		      struct bpf_spin_lock *spin_lock);
+
 
 int bpf_obj_name_cpy(char *dst, const char *src, unsigned int size);
 

include/uapi/linux/bpf.h

@@ -6917,6 +6917,17 @@ struct bpf_list_node {
 	__u64 :64;
 } __attribute__((aligned(8)));
 
+struct bpf_rb_root {
+	__u64 :64;
+	__u64 :64;
+} __attribute__((aligned(8)));
+
+struct bpf_rb_node {
+	__u64 :64;
+	__u64 :64;
+	__u64 :64;
+} __attribute__((aligned(8)));
+
 struct bpf_sysctl {
 	__u32	write;		/* Sysctl is being read (= 0) or written (= 1).
 				 * Allows 1,2,4-byte read, but no write.