bpf: btf: Introduce helpers for dynamic BTF set registration

This adds helpers for registering btf_id_set from modules and the
bpf_check_mod_kfunc_call callback that can be used to look them up.

With in kernel sets, the way this is supposed to work is, in kernel
callback looks up within the in-kernel kfunc whitelist, and then defers
to the dynamic BTF set lookup if it doesn't find the BTF id. If there is
no in-kernel BTF id set, this callback can be used directly.

Also fix includes for btf.h and bpfptr.h so that they can included in
isolation. This is in preparation for their usage in tcp_bbr, tcp_cubic
and tcp_dctcp modules in the next patch.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20211002011757.311265-4-memxor@gmail.com

include/linux/bpfptr.h

@@ -3,6 +3,7 @@
 #ifndef _LINUX_BPFPTR_H
 #define _LINUX_BPFPTR_H
 
+#include <linux/mm.h>
 #include <linux/sockptr.h>
 
 typedef sockptr_t bpfptr_t;

include/linux/btf.h

@@ -5,6 +5,7 @@
 #define _LINUX_BTF_H 1
 
 #include <linux/types.h>
+#include <linux/bpfptr.h>
 #include <uapi/linux/btf.h>
 #include <uapi/linux/bpf.h>
 
@@ -238,4 +239,39 @@ static inline const char *btf_name_by_offset(const struct btf *btf,
 }
 #endif
 
+struct kfunc_btf_id_set {
+	struct list_head list;
+	struct btf_id_set *set;
+	struct module *owner;
+};
+
+struct kfunc_btf_id_list;
+
+#ifdef CONFIG_DEBUG_INFO_BTF_MODULES
+void register_kfunc_btf_id_set(struct kfunc_btf_id_list *l,
+			       struct kfunc_btf_id_set *s);
+void unregister_kfunc_btf_id_set(struct kfunc_btf_id_list *l,
+				 struct kfunc_btf_id_set *s);
+bool bpf_check_mod_kfunc_call(struct kfunc_btf_id_list *klist, u32 kfunc_id,
+			      struct module *owner);
+#else
+static inline void register_kfunc_btf_id_set(struct kfunc_btf_id_list *l,
+					     struct kfunc_btf_id_set *s)
+{
+}
+static inline void unregister_kfunc_btf_id_set(struct kfunc_btf_id_list *l,
+					       struct kfunc_btf_id_set *s)
+{
+}
+static inline bool bpf_check_mod_kfunc_call(struct kfunc_btf_id_list *klist,
+					    u32 kfunc_id, struct module *owner)
+{
+	return false;
+}
+#endif
+
+#define DEFINE_KFUNC_BTF_ID_SET(set, name)                                     \
+	struct kfunc_btf_id_set name = { LIST_HEAD_INIT(name.list), (set),     \
+					 THIS_MODULE }
+
 #endif

kernel/bpf/btf.c

@@ -6343,3 +6343,55 @@ const struct bpf_func_proto bpf_btf_find_by_name_kind_proto = {
 };
 
 BTF_ID_LIST_GLOBAL_SINGLE(btf_task_struct_ids, struct, task_struct)
+
+/* BTF ID set registration API for modules */
+
+struct kfunc_btf_id_list {
+	struct list_head list;
+	struct mutex mutex;
+};
+
+#ifdef CONFIG_DEBUG_INFO_BTF_MODULES
+
+void register_kfunc_btf_id_set(struct kfunc_btf_id_list *l,
+			       struct kfunc_btf_id_set *s)
+{
+	mutex_lock(&l->mutex);
+	list_add(&s->list, &l->list);
+	mutex_unlock(&l->mutex);
+}
+EXPORT_SYMBOL_GPL(register_kfunc_btf_id_set);
+
+void unregister_kfunc_btf_id_set(struct kfunc_btf_id_list *l,
+				 struct kfunc_btf_id_set *s)
+{
+	mutex_lock(&l->mutex);
+	list_del_init(&s->list);
+	mutex_unlock(&l->mutex);
+}
+EXPORT_SYMBOL_GPL(unregister_kfunc_btf_id_set);
+
+bool bpf_check_mod_kfunc_call(struct kfunc_btf_id_list *klist, u32 kfunc_id,
+			      struct module *owner)
+{
+	struct kfunc_btf_id_set *s;
+
+	if (!owner)
+		return false;
+	mutex_lock(&klist->mutex);
+	list_for_each_entry(s, &klist->list, list) {
+		if (s->owner == owner && btf_id_set_contains(s->set, kfunc_id)) {
+			mutex_unlock(&klist->mutex);
+			return true;
+		}
+	}
+	mutex_unlock(&klist->mutex);
+	return false;
+}
+
+#endif
+
+#define DEFINE_KFUNC_BTF_ID_LIST(name)                                         \
+	struct kfunc_btf_id_list name = { LIST_HEAD_INIT(name.list),           \
+					  __MUTEX_INITIALIZER(name.mutex) };   \
+	EXPORT_SYMBOL_GPL(name)