bpf: Implement bpf iterator for hash maps

The bpf iterators for hash, percpu hash, lru hash
and lru percpu hash are implemented. During link time,
bpf_iter_reg->check_target() will check map type
and ensure the program access key/value region is
within the map defined key/value size limit.

For percpu hash and lru hash maps, the bpf program
will receive values for all cpus. The map element
bpf iterator infrastructure will prepare value
properly before passing the value pointer to the
bpf program.

This patch set supports readonly map keys and
read/write map values. It does not support deleting
map elements, e.g., from hash tables. If there is
a user case for this, the following mechanism can
be used to support map deletion for hashtab, etc.
  - permit a new bpf program return value, e.g., 2,
    to let bpf iterator know the map element should
    be removed.
  - since bucket lock is taken, the map element will be
    queued.
  - once bucket lock is released after all elements under
    this bucket are traversed, all to-be-deleted map
    elements can be deleted.

Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200723184114.590470-1-yhs@fb.com

1 files changed, 23 insertions, 1 deletions

diff --git a/kernel/bpf/map_iter.c b/kernel/bpf/map_iter.c
index 8a1f9b3355d0..bcb68b55bf65 100644
--- a/kernel/bpf/map_iter.c
+++ b/kernel/bpf/map_iter.c
@@ -101,7 +101,29 @@ static struct bpf_iter_reg bpf_map_reg_info = {
 static int bpf_iter_check_map(struct bpf_prog *prog,
 			      struct bpf_iter_aux_info *aux)
 {
-	return -EINVAL;
+	u32 key_acc_size, value_acc_size, key_size, value_size;
+	struct bpf_map *map = aux->map;
+	bool is_percpu = false;
+
+	if (map->map_type == BPF_MAP_TYPE_PERCPU_HASH ||
+	    map->map_type == BPF_MAP_TYPE_LRU_PERCPU_HASH)
+		is_percpu = true;
+	else if (map->map_type != BPF_MAP_TYPE_HASH &&
+		 map->map_type != BPF_MAP_TYPE_LRU_HASH)
+		return -EINVAL;
+
+	key_acc_size = prog->aux->max_rdonly_access;
+	value_acc_size = prog->aux->max_rdwr_access;
+	key_size = map->key_size;
+	if (!is_percpu)
+		value_size = map->value_size;
+	else
+		value_size = round_up(map->value_size, 8) * num_possible_cpus();
+
+	if (key_acc_size > key_size || value_acc_size > value_size)
+		return -EACCES;
+
+	return 0;
 }
 
 DEFINE_BPF_ITER_FUNC(bpf_map_elem, struct bpf_iter_meta *meta,