[PATCH net-next 6/7] bpf: allow eBPF programs to use maps

Alexei Starovoitov
2014-11-04T02:55:09Z

expose bpf_map_lookup_elem(), bpf_map_update_elem(), bpf_map_delete_elem()
map accessors to eBPF programs

Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>
---
Note, these helpers are exposed as '.gpl_only = false', so non-GPL eBPF programs
can use them. That was requested by AndyL and DavidL before.

include/linux/bpf.h | 5 +++
include/uapi/linux/bpf.h | 3 ++
kernel/bpf/Makefile | 2 +-
kernel/bpf/helpers.c | 88 ++++++++++++++++++++++++++++++++++++++++++++++
4 files changed, 97 insertions(+), 1 deletion(-)
create mode 100644 kernel/bpf/helpers.c

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 51e9242e4803..75e94eaa228b 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -133,4 +133,9 @@ struct bpf_prog *bpf_prog_get(u32 ufd);
/* verify correctness of eBPF program */
int bpf_check(struct bpf_prog *fp, union bpf_attr *attr);

+/* verifier prototypes for helper functions called from eBPF programs */
+extern struct bpf_func_proto bpf_map_lookup_elem_proto;
+extern struct bpf_func_proto bpf_map_update_elem_proto;
+extern struct bpf_func_proto bpf_map_delete_elem_proto;
+
#endif /* _LINUX_BPF_H */
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 9811d012b766..84a7fc3a23ec 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -160,6 +160,9 @@ union bpf_attr {
*/
enum bpf_func_id {
BPF_FUNC_unspec,
+ BPF_FUNC_map_lookup_elem, /* void *map_lookup_elem(&map, &key) */
+ BPF_FUNC_map_update_elem, /* int map_update_elem(&map, &key, &value, flags) */
+ BPF_FUNC_map_delete_elem, /* int map_delete_elem(&map, &key) */
__BPF_FUNC_MAX_ID,
};

diff --git a/kernel/bpf/Makefile b/kernel/bpf/Makefile
index 72ec98ba2d42..a5ae60f0b0a2 100644
--- a/kernel/bpf/Makefile
+++ b/kernel/bpf/Makefile
@@ -1,5 +1,5 @@
obj-y := core.o
-obj-$(CONFIG_BPF_SYSCALL) += syscall.o verifier.o hashtab.o arraymap.o
+obj-$(CONFIG_BPF_SYSCALL) += syscall.o verifier.o hashtab.o arraymap.o helpers.o
ifdef CONFIG_TEST_BPF
obj-$(CONFIG_BPF_SYSCALL) += test_stub.o
endif
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
new file mode 100644
index 000000000000..3fa78babe728
--- /dev/null
+++ b/kernel/bpf/helpers.c
@@ -0,0 +1,88 @@
+/* Copyright (c) 2011-2014 PLUMgrid, http://plumgrid.com
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of version 2 of the GNU General Public
+ * License as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ * General Public License for more details.
+ */
+#include <linux/bpf.h>
+#include <linux/rcupdate.h>
+
+/* called from eBPF program under rcu lock
+ *
+ * if kernel subsystem is allowing eBPF programs to call this function,
+ * inside its own verifier_ops->get_func_proto() callback it should return
+ * bpf_map_lookup_elem_proto, so that verifier can properly checks the arguments
+ */
+static u64 bpf_map_lookup_elem(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5)
+{
+ /* verifier checked that R1 contains a valid pointer to bpf_map
+ * and R2 points to a program stack and map->key_size bytes were
+ * initialized
+ */
+ struct bpf_map *map = (struct bpf_map *) (unsigned long) r1;
+ void *key = (void *) (unsigned long) r2;
+ void *value;
+
+ WARN_ON_ONCE(!rcu_read_lock_held());
+
+ value = map->ops->map_lookup_elem(map, key);
+
+ /* lookup() returns either pointer to element value or NULL
+ * which is the meaning of PTR_TO_MAP_VALUE_OR_NULL type
+ */
+ return (unsigned long) value;
+}
+
+struct bpf_func_proto bpf_map_lookup_elem_proto = {
+ .func = bpf_map_lookup_elem,
+ .gpl_only = false,
+ .ret_type = RET_PTR_TO_MAP_VALUE_OR_NULL,
+ .arg1_type = ARG_CONST_MAP_PTR,
+ .arg2_type = ARG_PTR_TO_MAP_KEY,
+};
+
+/* called from eBPF program under rcu lock */
+static u64 bpf_map_update_elem(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5)
+{
+ struct bpf_map *map = (struct bpf_map *) (unsigned long) r1;
+ void *key = (void *) (unsigned long) r2;
+ void *value = (void *) (unsigned long) r3;
+
+ WARN_ON_ONCE(!rcu_read_lock_held());
+
+ return map->ops->map_update_elem(map, key, value, r4);
+}
+
+struct bpf_func_proto bpf_map_update_elem_proto = {
+ .func = bpf_map_update_elem,
+ .gpl_only = false,
+ .ret_type = RET_INTEGER,
+ .arg1_type = ARG_CONST_MAP_PTR,
+ .arg2_type = ARG_PTR_TO_MAP_KEY,
+ .arg3_type = ARG_PTR_TO_MAP_VALUE,
+ .arg4_type = ARG_ANYTHING,
+};
+
+/* called from eBPF program under rcu lock */
+static u64 bpf_map_delete_elem(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5)
+{
+ struct bpf_map *map = (struct bpf_map *) (unsigned long) r1;
+ void *key = (void *) (unsigned long) r2;
+
+ WARN_ON_ONCE(!rcu_read_lock_held());
+
+ return map->ops->map_delete_elem(map, key);
+}
+
+struct bpf_func_proto bpf_map_delete_elem_proto = {
+ .func = bpf_map_delete_elem,
+ .gpl_only = false,
+ .ret_type = RET_INTEGER,
+ .arg1_type = ARG_CONST_MAP_PTR,
+ .arg2_type = ARG_PTR_TO_MAP_KEY,
+};
--
1.7.9.5