bpf: add btf_type_is_i{32,64} helpers

There are places in BPF code which check if a BTF type is an integer
of particular size. This code can be made simpler by using helpers.
Add new btf_type_is_i{32,64} helpers, and simplify code in a few
files. (Suggested by Eduard for a patch which copy-pasted such a
check [1].)

  v1 -> v2:
    * export less generic helpers (Eduard)
    * make subject less generic than in [v1] (Eduard)

[1] https://lore.kernel.org/bpf/[email protected]/
[v1] https://lore.kernel.org/bpf/[email protected]/

Suggested-by: Eduard Zingerman <[email protected]>
Signed-off-by: Anton Protopopov <[email protected]>
Acked-by: Eduard Zingerman <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Alexei Starovoitov <[email protected]>

Author: aspsk

include/linux/btf.h

@@ -221,6 +221,8 @@ bool btf_is_vmlinux(const struct btf *btf);
 struct module *btf_try_get_module(const struct btf *btf);
 u32 btf_nr_types(const struct btf *btf);
 struct btf *btf_base_btf(const struct btf *btf);
+bool btf_type_is_i32(const struct btf_type *t);
+bool btf_type_is_i64(const struct btf_type *t);
 bool btf_member_is_reg_int(const struct btf *btf, const struct btf_type *s,
 			   const struct btf_member *m,
 			   u32 expected_offset, u32 expected_size);

kernel/bpf/arraymap.c

@@ -530,8 +530,6 @@ static int array_map_check_btf(const struct bpf_map *map,
 			       const struct btf_type *key_type,
 			       const struct btf_type *value_type)
 {
-	u32 int_data;
-
 	/* One exception for keyless BTF: .bss/.data/.rodata map */
 	if (btf_type_is_void(key_type)) {
 		if (map->map_type != BPF_MAP_TYPE_ARRAY ||
@@ -544,14 +542,11 @@ static int array_map_check_btf(const struct bpf_map *map,
 		return 0;
 	}
 
-	if (BTF_INFO_KIND(key_type->info) != BTF_KIND_INT)
-		return -EINVAL;
-
-	int_data = *(u32 *)(key_type + 1);
-	/* bpf array can only take a u32 key. This check makes sure
+	/*
+	 * Bpf array can only take a u32 key. This check makes sure
 	 * that the btf matches the attr used during map_create.
 	 */
-	if (BTF_INT_BITS(int_data) != 32 || BTF_INT_OFFSET(int_data))
+	if (!btf_type_is_i32(key_type))
 		return -EINVAL;
 
 	return 0;

kernel/bpf/bpf_local_storage.c

@@ -722,13 +722,7 @@ int bpf_local_storage_map_check_btf(const struct bpf_map *map,
 				    const struct btf_type *key_type,
 				    const struct btf_type *value_type)
 {
-	u32 int_data;
-
-	if (BTF_INFO_KIND(key_type->info) != BTF_KIND_INT)
-		return -EINVAL;
-
-	int_data = *(u32 *)(key_type + 1);
-	if (BTF_INT_BITS(int_data) != 32 || BTF_INT_OFFSET(int_data))
+	if (!btf_type_is_i32(key_type))
 		return -EINVAL;
 
 	return 0;

kernel/bpf/btf.c

@@ -858,26 +858,37 @@ const struct btf_type *btf_type_by_id(const struct btf *btf, u32 type_id)
 EXPORT_SYMBOL_GPL(btf_type_by_id);
 
 /*
- * Regular int is not a bit field and it must be either
- * u8/u16/u32/u64 or __int128.
+ * Check that the type @t is a regular int. This means that @t is not
+ * a bit field and it has the same size as either of u8/u16/u32/u64
+ * or __int128. If @expected_size is not zero, then size of @t should
+ * be the same. A caller should already have checked that the type @t
+ * is an integer.
  */
+static bool __btf_type_int_is_regular(const struct btf_type *t, size_t expected_size)
+{
+	u32 int_data = btf_type_int(t);
+	u8 nr_bits = BTF_INT_BITS(int_data);
+	u8 nr_bytes = BITS_ROUNDUP_BYTES(nr_bits);
+
+	return BITS_PER_BYTE_MASKED(nr_bits) == 0 &&
+	       BTF_INT_OFFSET(int_data) == 0 &&
+	       (nr_bytes <= 16 && is_power_of_2(nr_bytes)) &&
+	       (expected_size == 0 || nr_bytes == expected_size);
+}
+
 static bool btf_type_int_is_regular(const struct btf_type *t)
 {
-	u8 nr_bits, nr_bytes;
-	u32 int_data;
+	return __btf_type_int_is_regular(t, 0);
+}
 
-	int_data = btf_type_int(t);
-	nr_bits = BTF_INT_BITS(int_data);
-	nr_bytes = BITS_ROUNDUP_BYTES(nr_bits);
-	if (BITS_PER_BYTE_MASKED(nr_bits) ||
-	    BTF_INT_OFFSET(int_data) ||
-	    (nr_bytes != sizeof(u8) && nr_bytes != sizeof(u16) &&
-	     nr_bytes != sizeof(u32) && nr_bytes != sizeof(u64) &&
-	     nr_bytes != (2 * sizeof(u64)))) {
-		return false;
-	}
+bool btf_type_is_i32(const struct btf_type *t)
+{
+	return btf_type_is_int(t) && __btf_type_int_is_regular(t, 4);
+}
 
-	return true;
+bool btf_type_is_i64(const struct btf_type *t)
+{
+	return btf_type_is_int(t) && __btf_type_int_is_regular(t, 8);
 }
 
 /*

kernel/bpf/local_storage.c

@@ -394,17 +394,10 @@ static int cgroup_storage_check_btf(const struct bpf_map *map,
 		if (!btf_member_is_reg_int(btf, key_type, m, offset, size))
 			return -EINVAL;
 	} else {
-		u32 int_data;
-
 		/*
 		 * Key is expected to be u64, which stores the cgroup_inode_id
 		 */
-
-		if (BTF_INFO_KIND(key_type->info) != BTF_KIND_INT)
-			return -EINVAL;
-
-		int_data = *(u32 *)(key_type + 1);
-		if (BTF_INT_BITS(int_data) != 64 || BTF_INT_OFFSET(int_data))
+		if (!btf_type_is_i64(key_type))
 			return -EINVAL;
 	}