[RFC PATCH bpf-next 06/11] bpf: Add bpf_rbtree_{lock,unlock} helpers

[Dave Marchevsky <davemarchevsky@fb.com>]

These helpers are equivalent to bpf_spin_{lock,unlock}, but the verifier
doesn't try to enforce that no helper calls occur when there's an active
spin lock.

[ TODO: Currently the verifier doesn't do _anything_ spinlock related
when it sees one of these, including setting active_spin_lock. This is
probably too lenient. Also, EXPORT_SYMBOL for internal lock helpers
might not be the best code structure. ]

Future patches will add enforcement of "rbtree helpers must always be
called when lock is held" constraint.

Signed-off-by: Dave Marchevsky <davemarchevsky@fb.com>
---
 include/uapi/linux/bpf.h       | 20 ++++++++++++++++++++
 kernel/bpf/helpers.c           | 12 ++++++++++--
 kernel/bpf/rbtree.c            | 29 +++++++++++++++++++++++++++++
 kernel/bpf/verifier.c          |  2 ++
 tools/include/uapi/linux/bpf.h | 20 ++++++++++++++++++++
 5 files changed, 81 insertions(+), 2 deletions(-)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index c677d92de3bc..d21e2c99ea14 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -5391,6 +5391,24 @@ union bpf_attr {
  *
  *	Return
  *		Ptr to lock
+ *
+ * void *bpf_rbtree_lock(struct bpf_spin_lock *lock)
+ *	Description
+ *		Like bpf_spin_lock helper, but use separate helper for now
+ *		as we don't want this helper to have special meaning to the verifier
+ *		so that we can do rbtree helper calls between rbtree_lock/unlock
+ *
+ *	Return
+ *		0
+ *
+ * void *bpf_rbtree_unlock(struct bpf_spin_lock *lock)
+ *	Description
+ *		Like bpf_spin_unlock helper, but use separate helper for now
+ *		as we don't want this helper to have special meaning to the verifier
+ *		so that we can do rbtree helper calls between rbtree_lock/unlock
+ *
+ *	Return
+ *		0
  */
 #define __BPF_FUNC_MAPPER(FN)		\
 	FN(unspec),			\
@@ -5607,6 +5625,8 @@ union bpf_attr {
 	FN(rbtree_remove),		\
 	FN(rbtree_free_node),		\
 	FN(rbtree_get_lock),		\
+	FN(rbtree_lock),		\
+	FN(rbtree_unlock),		\
 	/* */
 
 /* integer value in 'imm' field of BPF_CALL instruction selects which helper
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 257a808bb767..fa2dba1dcec8 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -303,7 +303,7 @@ static inline void __bpf_spin_unlock(struct bpf_spin_lock *lock)
 
 static DEFINE_PER_CPU(unsigned long, irqsave_flags);
 
-static inline void __bpf_spin_lock_irqsave(struct bpf_spin_lock *lock)
+inline void __bpf_spin_lock_irqsave(struct bpf_spin_lock *lock)
 {
 	unsigned long flags;
 
@@ -311,6 +311,7 @@ static inline void __bpf_spin_lock_irqsave(struct bpf_spin_lock *lock)
 	__bpf_spin_lock(lock);
 	__this_cpu_write(irqsave_flags, flags);
 }
+EXPORT_SYMBOL(__bpf_spin_lock_irqsave);
 
 notrace BPF_CALL_1(bpf_spin_lock, struct bpf_spin_lock *, lock)
 {
@@ -325,7 +326,7 @@ const struct bpf_func_proto bpf_spin_lock_proto = {
 	.arg1_type	= ARG_PTR_TO_SPIN_LOCK,
 };
 
-static inline void __bpf_spin_unlock_irqrestore(struct bpf_spin_lock *lock)
+inline void __bpf_spin_unlock_irqrestore(struct bpf_spin_lock *lock)
 {
 	unsigned long flags;
 
@@ -333,6 +334,7 @@ static inline void __bpf_spin_unlock_irqrestore(struct bpf_spin_lock *lock)
 	__bpf_spin_unlock(lock);
 	local_irq_restore(flags);
 }
+EXPORT_SYMBOL(__bpf_spin_unlock_irqrestore);
 
 notrace BPF_CALL_1(bpf_spin_unlock, struct bpf_spin_lock *, lock)
 {
@@ -1588,6 +1590,8 @@ const struct bpf_func_proto bpf_rbtree_find_proto __weak;
 const struct bpf_func_proto bpf_rbtree_remove_proto __weak;
 const struct bpf_func_proto bpf_rbtree_free_node_proto __weak;
 const struct bpf_func_proto bpf_rbtree_get_lock_proto __weak;
+const struct bpf_func_proto bpf_rbtree_lock_proto __weak;
+const struct bpf_func_proto bpf_rbtree_unlock_proto __weak;
 
 const struct bpf_func_proto *
 bpf_base_func_proto(enum bpf_func_id func_id)
@@ -1689,6 +1693,10 @@ bpf_base_func_proto(enum bpf_func_id func_id)
 		return &bpf_rbtree_free_node_proto;
 	case BPF_FUNC_rbtree_get_lock:
 		return &bpf_rbtree_get_lock_proto;
+	case BPF_FUNC_rbtree_lock:
+		return &bpf_rbtree_lock_proto;
+	case BPF_FUNC_rbtree_unlock:
+		return &bpf_rbtree_unlock_proto;
 	default:
 		break;
 	}
diff --git a/kernel/bpf/rbtree.c b/kernel/bpf/rbtree.c
index c6f0a2a083f6..bf2e30af82ec 100644
--- a/kernel/bpf/rbtree.c
+++ b/kernel/bpf/rbtree.c
@@ -262,6 +262,35 @@ const struct bpf_func_proto bpf_rbtree_get_lock_proto = {
 	.arg1_type = ARG_CONST_MAP_PTR,
 };
 
+extern void __bpf_spin_unlock_irqrestore(struct bpf_spin_lock *lock);
+extern void __bpf_spin_lock_irqsave(struct bpf_spin_lock *lock);
+
+BPF_CALL_1(bpf_rbtree_lock, void *, lock)
+{
+	__bpf_spin_lock_irqsave((struct bpf_spin_lock *)lock);
+	return 0;
+}
+
+const struct bpf_func_proto bpf_rbtree_lock_proto = {
+	.func = bpf_rbtree_lock,
+	.gpl_only = true,
+	.ret_type = RET_INTEGER,
+	.arg1_type = ARG_PTR_TO_SPIN_LOCK,
+};
+
+BPF_CALL_1(bpf_rbtree_unlock, void *, lock)
+{
+	__bpf_spin_unlock_irqrestore((struct bpf_spin_lock *)lock);
+	return 0;
+}
+
+const struct bpf_func_proto bpf_rbtree_unlock_proto = {
+	.func = bpf_rbtree_unlock,
+	.gpl_only = true,
+	.ret_type = RET_INTEGER,
+	.arg1_type = ARG_PTR_TO_SPIN_LOCK,
+};
+
 BTF_ID_LIST_SINGLE(bpf_rbtree_map_btf_ids, struct, bpf_rbtree)
 const struct bpf_map_ops rbtree_map_ops = {
 	.map_meta_equal = bpf_map_meta_equal,
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 535f673882cd..174a355d97fd 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -6047,6 +6047,8 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 arg,
 		} else if (meta->func_id == BPF_FUNC_spin_unlock) {
 			if (process_spin_lock(env, regno, false))
 				return -EACCES;
+		} else if (meta->func_id == BPF_FUNC_rbtree_lock ||
+			   meta->func_id == BPF_FUNC_rbtree_unlock) { // Do nothing for now
 		} else {
 			verbose(env, "verifier internal error\n");
 			return -EFAULT;
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index c677d92de3bc..d21e2c99ea14 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -5391,6 +5391,24 @@ union bpf_attr {
  *
  *	Return
  *		Ptr to lock
+ *
+ * void *bpf_rbtree_lock(struct bpf_spin_lock *lock)
+ *	Description
+ *		Like bpf_spin_lock helper, but use separate helper for now
+ *		as we don't want this helper to have special meaning to the verifier
+ *		so that we can do rbtree helper calls between rbtree_lock/unlock
+ *
+ *	Return
+ *		0
+ *
+ * void *bpf_rbtree_unlock(struct bpf_spin_lock *lock)
+ *	Description
+ *		Like bpf_spin_unlock helper, but use separate helper for now
+ *		as we don't want this helper to have special meaning to the verifier
+ *		so that we can do rbtree helper calls between rbtree_lock/unlock
+ *
+ *	Return
+ *		0
  */
 #define __BPF_FUNC_MAPPER(FN)		\
 	FN(unspec),			\
@@ -5607,6 +5625,8 @@ union bpf_attr {
 	FN(rbtree_remove),		\
 	FN(rbtree_free_node),		\
 	FN(rbtree_get_lock),		\
+	FN(rbtree_lock),		\
+	FN(rbtree_unlock),		\
 	/* */
 
 /* integer value in 'imm' field of BPF_CALL instruction selects which helper
-- 
2.30.2