bpf: decouple btf from seq bpf fs dump and enable more maps

Commit a26ca7c982cb ("bpf: btf: Add pretty print support to
the basic arraymap") and 699c86d6ec21 ("bpf: btf: add pretty
print for hash/lru_hash maps") enabled support for BTF and
dumping via BPF fs for array and hash/lru map. However, both
can be decoupled from each other such that regular BPF maps
can be supported for attaching BTF key/value information,
while not all maps necessarily need to dump via map_seq_show_elem()
callback.

The basic sanity check which is a prerequisite for all maps
is that key/value size has to match in any case, and some maps
can have extra checks via map_check_btf() callback, e.g.
probing certain types or indicating no support in general. With
that we can also enable retrieving BTF info for per-cpu map
types and lpm.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Yonghong Song <yhs@fb.com>

1 files changed, 32 insertions, 4 deletions

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 57f4d076141b..43727ed0d94a 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -103,6 +103,7 @@ int bpf_check_uarg_tail_zero(void __user *uaddr,
 const struct bpf_map_ops bpf_map_offload_ops = {
 	.map_alloc = bpf_map_offload_map_alloc,
 	.map_free = bpf_map_offload_map_free,
+	.map_check_btf = map_check_no_btf,
 };
 
 static struct bpf_map *find_and_alloc_map(union bpf_attr *attr)
@@ -455,6 +456,34 @@ static int bpf_obj_name_cpy(char *dst, const char *src)
 	return 0;
 }
 
+int map_check_no_btf(const struct bpf_map *map,
+		     const struct btf_type *key_type,
+		     const struct btf_type *value_type)
+{
+	return -ENOTSUPP;
+}
+
+static int map_check_btf(const struct bpf_map *map, const struct btf *btf,
+			 u32 btf_key_id, u32 btf_value_id)
+{
+	const struct btf_type *key_type, *value_type;
+	u32 key_size, value_size;
+	int ret = 0;
+
+	key_type = btf_type_id_size(btf, &btf_key_id, &key_size);
+	if (!key_type || key_size != map->key_size)
+		return -EINVAL;
+
+	value_type = btf_type_id_size(btf, &btf_value_id, &value_size);
+	if (!value_type || value_size != map->value_size)
+		return -EINVAL;
+
+	if (map->ops->map_check_btf)
+		ret = map->ops->map_check_btf(map, key_type, value_type);
+
+	return ret;
+}
+
 #define BPF_MAP_CREATE_LAST_FIELD btf_value_type_id
 /* called via syscall */
 static int map_create(union bpf_attr *attr)
@@ -489,8 +518,7 @@ static int map_create(union bpf_attr *attr)
 	atomic_set(&map->refcnt, 1);
 	atomic_set(&map->usercnt, 1);
 
-	if (bpf_map_support_seq_show(map) &&
-	    (attr->btf_key_type_id || attr->btf_value_type_id)) {
+	if (attr->btf_key_type_id || attr->btf_value_type_id) {
 		struct btf *btf;
 
 		if (!attr->btf_key_type_id || !attr->btf_value_type_id) {
@@ -504,8 +532,8 @@ static int map_create(union bpf_attr *attr)
 			goto free_map_nouncharge;
 		}
 
-		err = map->ops->map_check_btf(map, btf, attr->btf_key_type_id,
-					      attr->btf_value_type_id);
+		err = map_check_btf(map, btf, attr->btf_key_type_id,
+				    attr->btf_value_type_id);
 		if (err) {
 			btf_put(btf);
 			goto free_map_nouncharge;