bpf: introduce BPF syscall and maps

BPF syscall is a multiplexor for a range of different operations on eBPF.
This patch introduces syscall with single command to create a map.
Next patch adds commands to access maps.

'maps' is a generic storage of different types for sharing data between kernel
and userspace.

Userspace example:
/* this syscall wrapper creates a map with given type and attributes
 * and returns map_fd on success.
 * use close(map_fd) to delete the map
 */
int bpf_create_map(enum bpf_map_type map_type, int key_size,
                   int value_size, int max_entries)
{
    union bpf_attr attr = {
        .map_type = map_type,
        .key_size = key_size,
        .value_size = value_size,
        .max_entries = max_entries
    };

    return bpf(BPF_MAP_CREATE, &attr, sizeof(attr));
}

'union bpf_attr' is backwards compatible with future extensions.

More details in Documentation/networking/filter.txt and in manpage

Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 170 insertions, 1 deletions

diff --git a/kernel/bpf/Makefile b/kernel/bpf/Makefile
index 6a71145e2769..e9f7334ed07a 100644
--- a/kernel/bpf/Makefile
+++ b/kernel/bpf/Makefile
@@ -1 +1 @@
-obj-y := core.o
+obj-y := core.o syscall.o
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
new file mode 100644
index 000000000000..428a0e23adc0
--- /dev/null
+++ b/kernel/bpf/syscall.c
@@ -0,0 +1,169 @@
+/* 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/syscalls.h>
+#include <linux/slab.h>
+#include <linux/anon_inodes.h>
+
+static LIST_HEAD(bpf_map_types);
+
+static struct bpf_map *find_and_alloc_map(union bpf_attr *attr)
+{
+        struct bpf_map_type_list *tl;
+        struct bpf_map *map;
+
+        list_for_each_entry(tl, &bpf_map_types, list_node) {
+                if (tl->type == attr->map_type) {
+                        map = tl->ops->map_alloc(attr);
+                        if (IS_ERR(map))
+                                return map;
+                        map->ops = tl->ops;
+                        map->map_type = attr->map_type;
+                        return map;
+                }
+        }
+        return ERR_PTR(-EINVAL);
+}
+
+/* boot time registration of different map implementations */
+void bpf_register_map_type(struct bpf_map_type_list *tl)
+{
+        list_add(&tl->list_node, &bpf_map_types);
+}
+
+/* called from workqueue */
+static void bpf_map_free_deferred(struct work_struct *work)
+{
+        struct bpf_map *map = container_of(work, struct bpf_map, work);
+
+        /* implementation dependent freeing */
+        map->ops->map_free(map);
+}
+
+/* decrement map refcnt and schedule it for freeing via workqueue
+ * (unrelying map implementation ops->map_free() might sleep)
+ */
+void bpf_map_put(struct bpf_map *map)
+{
+        if (atomic_dec_and_test(&map->refcnt)) {
+                INIT_WORK(&map->work, bpf_map_free_deferred);
+                schedule_work(&map->work);
+        }
+}
+
+static int bpf_map_release(struct inode *inode, struct file *filp)
+{
+        struct bpf_map *map = filp->private_data;
+
+        bpf_map_put(map);
+        return 0;
+}
+
+static const struct file_operations bpf_map_fops = {
+        .release = bpf_map_release,
+};
+
+/* helper macro to check that unused fields 'union bpf_attr' are zero */
+#define CHECK_ATTR(CMD) \
+        memchr_inv((void *) &attr->CMD##_LAST_FIELD + \
+                   sizeof(attr->CMD##_LAST_FIELD), 0, \
+                   sizeof(*attr) - \
+                   offsetof(union bpf_attr, CMD##_LAST_FIELD) - \
+                   sizeof(attr->CMD##_LAST_FIELD)) != NULL
+
+#define BPF_MAP_CREATE_LAST_FIELD max_entries
+/* called via syscall */
+static int map_create(union bpf_attr *attr)
+{
+        struct bpf_map *map;
+        int err;
+
+        err = CHECK_ATTR(BPF_MAP_CREATE);
+        if (err)
+                return -EINVAL;
+
+        /* find map type and init map: hashtable vs rbtree vs bloom vs ... */
+        map = find_and_alloc_map(attr);
+        if (IS_ERR(map))
+                return PTR_ERR(map);
+
+        atomic_set(&map->refcnt, 1);
+
+        err = anon_inode_getfd("bpf-map", &bpf_map_fops, map, O_RDWR | O_CLOEXEC);
+
+        if (err < 0)
+                /* failed to allocate fd */
+                goto free_map;
+
+        return err;
+
+free_map:
+        map->ops->map_free(map);
+        return err;
+}
+
+SYSCALL_DEFINE3(bpf, int, cmd, union bpf_attr __user *, uattr, unsigned int, size)
+{
+        union bpf_attr attr = {};
+        int err;
+
+        /* the syscall is limited to root temporarily. This restriction will be
+         * lifted when security audit is clean. Note that eBPF+tracing must have
+         * this restriction, since it may pass kernel data to user space
+         */
+        if (!capable(CAP_SYS_ADMIN))
+                return -EPERM;
+
+        if (!access_ok(VERIFY_READ, uattr, 1))
+                return -EFAULT;
+
+        if (size > PAGE_SIZE)   /* silly large */
+                return -E2BIG;
+
+        /* If we're handed a bigger struct than we know of,
+         * ensure all the unknown bits are 0 - i.e. new
+         * user-space does not rely on any kernel feature
+         * extensions we dont know about yet.
+         */
+        if (size > sizeof(attr)) {
+                unsigned char __user *addr;
+                unsigned char __user *end;
+                unsigned char val;
+
+                addr = (void __user *)uattr + sizeof(attr);
+                end  = (void __user *)uattr + size;
+
+                for (; addr < end; addr++) {
+                        err = get_user(val, addr);
+                        if (err)
+                                return err;
+                        if (val)
+                                return -E2BIG;
+                }
+                size = sizeof(attr);
+        }
+
+        /* copy attributes from user space, may be less than sizeof(bpf_attr) */
+        if (copy_from_user(&attr, uattr, size) != 0)
+                return -EFAULT;
+
+        switch (cmd) {
+        case BPF_MAP_CREATE:
+                err = map_create(&attr);
+                break;
+        default:
+                err = -EINVAL;
+                break;
+        }
+
+        return err;
+}