Subject: [PATCH bpf-next v2 03/10] bpf: btf: Introduce helpers for dynamic BTF set registration

From: Kumar Kartikeya Dwivedi <[email-masked]>
Date: Tue, 14 Sep 2021 18:07:42 +0530

This adds helpers for registering btf_id_set from modules and the
check_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 <[email-masked]>
---
 include/linux/bpfptr.h |  1 +
 include/linux/btf.h    | 32 ++++++++++++++++++++++++++
 kernel/bpf/btf.c       | 51 ++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 84 insertions(+)

diff --git a/include/linux/bpfptr.h b/include/linux/bpfptr.h
index 546e27fc6d46..46e1757d06a3 100644
--- a/include/linux/bpfptr.h
+++ b/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;
diff --git a/include/linux/btf.h b/include/linux/btf.h
index 214fde93214b..e29a486d09d4 100644
--- a/include/linux/btf.h
+++ b/include/linux/btf.h
@@ -5,8 +5,10 @@
 #define _LINUX_BTF_H 1
 
 #include <linux/types.h>
+#include <linux/bpfptr.h>
 #include <uapi/linux/btf.h>
 #include <uapi/linux/bpf.h>
+#include <linux/mutex.h>
 
 #define BTF_TYPE_EMIT(type) ((void)(type *)0)
 #define BTF_TYPE_EMIT_ENUM(enum_val) ((void)enum_val)
@@ -238,4 +240,34 @@ 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);
+#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)
+{
+}
+#endif
+
+#define DECLARE_CHECK_KFUNC_CALLBACK(type)                                     \
+	bool __bpf_check_##type##_kfunc_call(u32 kfunc_id, struct module *owner)
+#define DEFINE_KFUNC_BTF_ID_SET(set, name)                                     \
+	struct kfunc_btf_id_set name = { LIST_HEAD_INIT(name.list), (set),     \
+					 THIS_MODULE }
+
 #endif
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index dfe61df4f974..eecafed56300 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -6215,3 +6215,54 @@ const struct bpf_func_proto bpf_btf_find_by_name_kind_proto = {
 };
 
 BTF_ID_LIST_GLOBAL_SINGLE(btf_task_struct_ids, struct, task_struct)
+
+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);
+
+#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)
+
+#define DEFINE_CHECK_KFUNC_CALLBACK(type, list_name)                           \
+	bool __bpf_check_##type##_kfunc_call(u32 kfunc_id,                     \
+					     struct module *owner)             \
+	{                                                                      \
+		struct kfunc_btf_id_set *s;                                    \
+		if (!owner || !IS_ENABLED(CONFIG_DEBUG_INFO_BTF_MODULES))      \
+			return false;                                          \
+		mutex_lock(&list_name.mutex);                                  \
+		list_for_each_entry(s, &list_name.list, list) {                \
+			if (s->owner == owner &&                               \
+			    btf_id_set_contains(s->set, kfunc_id)) {           \
+				mutex_unlock(&list_name.mutex);                \
+				return true;                                   \
+			}                                                      \
+		}                                                              \
+		mutex_unlock(&list_name.mutex);                                \
+		return false;                                                  \
+	}
-- 
2.33.0