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>

1 files changed, 40 insertions, 0 deletions

diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 2dae44581922..192184b5156e 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -1772,6 +1772,46 @@ unlock:
 	}
 }
 
+/* Like rbtree_postorder_for_each_entry_safe, but 'pos' and 'n' are
+ * 'rb_node *', so field name of rb_node within containing struct is not
+ * needed.
+ *
+ * Since bpf_rb_tree's node type has a corresponding struct btf_field with
+ * graph_root.node_offset, it's not necessary to know field name
+ * or type of node struct
+ */
+#define bpf_rbtree_postorder_for_each_entry_safe(pos, n, root) \
+	for (pos = rb_first_postorder(root); \
+	    pos && ({ n = rb_next_postorder(pos); 1; }); \
+	    pos = n)
+
+void bpf_rb_root_free(const struct btf_field *field, void *rb_root,
+		      struct bpf_spin_lock *spin_lock)
+{
+	struct rb_root_cached orig_root, *root = rb_root;
+	struct rb_node *pos, *n;
+	void *obj;
+
+	BUILD_BUG_ON(sizeof(struct rb_root_cached) > sizeof(struct bpf_rb_root));
+	BUILD_BUG_ON(__alignof__(struct rb_root_cached) > __alignof__(struct bpf_rb_root));
+
+	__bpf_spin_lock_irqsave(spin_lock);
+	orig_root = *root;
+	*root = RB_ROOT_CACHED;
+	__bpf_spin_unlock_irqrestore(spin_lock);
+
+	bpf_rbtree_postorder_for_each_entry_safe(pos, n, &orig_root.rb_root) {
+		obj = pos;
+		obj -= field->graph_root.node_offset;
+
+		bpf_obj_free_fields(field->graph_root.value_rec, obj);
+
+		migrate_disable();
+		bpf_mem_free(&bpf_global_ma, obj);
+		migrate_enable();
+	}
+}
+
 __diag_push();
 __diag_ignore_all("-Wmissing-prototypes",
 		  "Global functions as their definitions will be in vmlinux BTF");