[PATCH] sync map refs

[Daniel Borkmann]

Signed-off-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
---
 include/linux/bpf.h      |  1 +
 include/uapi/linux/bpf.h |  1 +
 kernel/bpf/arraymap.c    |  1 +
 kernel/bpf/hashtab.c     |  1 +
 kernel/bpf/map_in_map.c  |  6 ++++++
 kernel/bpf/map_in_map.h  |  1 +
 kernel/bpf/syscall.c     | 24 ++++++++++++++++++++++++
 7 files changed, 35 insertions(+)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 5b5ad95..7b51f86 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -34,6 +34,7 @@ struct bpf_map_ops {
 	void (*map_free)(struct bpf_map *map);
 	int (*map_get_next_key)(struct bpf_map *map, void *key, void *next_key);
 	void (*map_release_uref)(struct bpf_map *map);
+	int (*map_sync_refs)(struct bpf_map *map);

 	/* funcs callable from userspace and from eBPF programs */
 	void *(*map_lookup_elem)(struct bpf_map *map, void *key);
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 8701139..e6ec1de 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -98,6 +98,7 @@ enum bpf_cmd {
 	BPF_BTF_LOAD,
 	BPF_BTF_GET_FD_BY_ID,
 	BPF_TASK_FD_QUERY,
+	BPF_MAP_SYNC_REFS,
 };

 enum bpf_map_type {
diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c
index 544e58f..ddaf42a 100644
--- a/kernel/bpf/arraymap.c
+++ b/kernel/bpf/arraymap.c
@@ -748,5 +748,6 @@ const struct bpf_map_ops array_of_maps_map_ops = {
 	.map_fd_get_ptr = bpf_map_fd_get_ptr,
 	.map_fd_put_ptr = bpf_map_fd_put_ptr,
 	.map_fd_sys_lookup_elem = bpf_map_fd_sys_lookup_elem,
+	.map_sync_refs = bpf_map_sync_refs,
 	.map_gen_lookup = array_of_map_gen_lookup,
 };
diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
index 513d9df..05380ea 100644
--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c
@@ -1407,5 +1407,6 @@ const struct bpf_map_ops htab_of_maps_map_ops = {
 	.map_fd_get_ptr = bpf_map_fd_get_ptr,
 	.map_fd_put_ptr = bpf_map_fd_put_ptr,
 	.map_fd_sys_lookup_elem = bpf_map_fd_sys_lookup_elem,
+	.map_sync_refs = bpf_map_sync_refs,
 	.map_gen_lookup = htab_of_map_gen_lookup,
 };
diff --git a/kernel/bpf/map_in_map.c b/kernel/bpf/map_in_map.c
index 1da5746..698a50f 100644
--- a/kernel/bpf/map_in_map.c
+++ b/kernel/bpf/map_in_map.c
@@ -96,6 +96,12 @@ void bpf_map_fd_put_ptr(void *ptr)
 	bpf_map_put(ptr);
 }

+int bpf_map_sync_refs(struct bpf_map *map)
+{
+	synchronize_rcu();
+	return 0;
+}
+
 u32 bpf_map_fd_sys_lookup_elem(void *ptr)
 {
 	return ((struct bpf_map *)ptr)->id;
diff --git a/kernel/bpf/map_in_map.h b/kernel/bpf/map_in_map.h
index 6183db9..ac02456 100644
--- a/kernel/bpf/map_in_map.h
+++ b/kernel/bpf/map_in_map.h
@@ -19,6 +19,7 @@ bool bpf_map_meta_equal(const struct bpf_map *meta0,
 void *bpf_map_fd_get_ptr(struct bpf_map *map, struct file *map_file,
 			 int ufd);
 void bpf_map_fd_put_ptr(void *ptr);
+int bpf_map_sync_refs(struct bpf_map *map);
 u32 bpf_map_fd_sys_lookup_elem(void *ptr);

 #endif
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index a31a1ba..b1286cc 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -896,6 +896,27 @@ static int map_get_next_key(union bpf_attr *attr)
 	return err;
 }

+#define BPF_MAP_SYNC_REFS_LAST_FIELD map_fd
+
+static int map_sync_refs(union bpf_attr *attr)
+{
+	int err = -ENOTSUPP, ufd = attr->map_fd;
+	struct bpf_map *map;
+	struct fd f;
+
+	if (CHECK_ATTR(BPF_MAP_SYNC_REFS))
+		return -EINVAL;
+
+	f = fdget(ufd);
+	map = __bpf_map_get(f);
+	if (IS_ERR(map))
+		return PTR_ERR(map);
+	if (map->ops->map_sync_refs)
+		err = map->ops->map_sync_refs(map);
+	fdput(f);
+	return err;
+}
+
 static const struct bpf_prog_ops * const bpf_prog_types[] = {
 #define BPF_PROG_TYPE(_id, _name) \
 	[_id] = & _name ## _prog_ops,
@@ -2303,6 +2324,9 @@ SYSCALL_DEFINE3(bpf, int, cmd, union bpf_attr __user *, uattr, unsigned int, siz
 	case BPF_MAP_GET_NEXT_KEY:
 		err = map_get_next_key(&attr);
 		break;
+	case BPF_MAP_SYNC_REFS:
+		err = map_sync_refs(&attr);
+		break;
 	case BPF_PROG_LOAD:
 		err = bpf_prog_load(&attr);
 		break;
-- 
2.9.5