bpf: allow eBPF programs to use maps

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>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 90 insertions, 1 deletions

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..9e3414d85459
--- /dev/null
+++ b/kernel/bpf/helpers.c
@@ -0,0 +1,89 @@
+/* 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>
+
+/* 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 check the arguments
+ *
+ * Different map implementations will rely on rcu in map methods
+ * lookup/update/delete, therefore eBPF programs must run under rcu lock
+ * if program is allowed to access maps, so check rcu_read_lock_held in
+ * all three functions.
+ */
+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,
+};
+
+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,
+};
+
+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,
+};