Merge branch 'fix-BTF-enum'

Yoshiki Komachi says:

====================
btf_enum_check_member() checked if the size of "enum" as a struct
member exceeded struct_size or not. Then, the function compared it
with the size of "int". Although the size of "enum" is 4-byte by
default (i.e., equivalent to "int"), the packing feature enables
us to reduce it, as illustrated by the following example:

struct A {
        char m;
        enum { E0, E1 } __attribute__((packed)) n;
};

With such a setup above, the bpf loader gave an error attempting
to load it:

------------------------------------------------------------------
...

[3] ENUM (anon) size=1 vlen=2
        E0 val=0
        E1 val=1
[4] STRUCT A size=2 vlen=2
        m type_id=2 bits_offset=0
        n type_id=3 bits_offset=8

[4] STRUCT A size=2 vlen=2
        n type_id=3 bits_offset=8 Member exceeds struct_size

libbpf: Error loading .BTF into kernel: -22.

------------------------------------------------------------------

The related issue was previously fixed by the commit 9eea9849 ("bpf:
fix BTF verification of enums"). On the other hand, this series fixes
this issue as well, and adds a selftest program for it.

Changes in v2:
- change an example in commit message based on Andrii's review
- add a selftest program for packed "enum" type members in struct/union
====================
Acked-by: Andrii Nakryiko <andriin@fb.com>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

kernel/bpf/btf.c

@@ -2418,7 +2418,7 @@ static int btf_enum_check_member(struct btf_verifier_env *env,
 
 	struct_size = struct_type->size;
 	bytes_offset = BITS_ROUNDDOWN_BYTES(struct_bits_off);
-	if (struct_size - bytes_offset < sizeof(int)) {
+	if (struct_size - bytes_offset < member_type->size) {
 		btf_verifier_log_member(env, struct_type, member,
 					"Member exceeds struct_size");
 		return -EINVAL;

tools/testing/selftests/bpf/test_btf.c

@@ -1062,6 +1062,48 @@ static struct btf_raw_test raw_tests[] = {
 	.err_str = "Member exceeds struct_size",
 },
 
+/* Test member unexceeds the size of struct
+ *
+ * enum E {
+ *     E0,
+ *     E1,
+ * };
+ *
+ * struct A {
+ *     char m;
+ *     enum E __attribute__((packed)) n;
+ * };
+ */
+{
+	.descr = "size check test #5",
+	.raw_types = {
+		/* int */			/* [1] */
+		BTF_TYPE_INT_ENC(0, BTF_INT_SIGNED, 0, 32, sizeof(int)),
+		/* char */			/* [2] */
+		BTF_TYPE_INT_ENC(0, BTF_INT_SIGNED, 0, 8, 1),
+		/* enum E { */			/* [3] */
+		BTF_TYPE_ENC(NAME_TBD, BTF_INFO_ENC(BTF_KIND_ENUM, 0, 2), 1),
+		BTF_ENUM_ENC(NAME_TBD, 0),
+		BTF_ENUM_ENC(NAME_TBD, 1),
+		/* } */
+		/* struct A { */		/* [4] */
+		BTF_TYPE_ENC(NAME_TBD, BTF_INFO_ENC(BTF_KIND_STRUCT, 0, 2), 2),
+		BTF_MEMBER_ENC(NAME_TBD, 2, 0),	/* char m; */
+		BTF_MEMBER_ENC(NAME_TBD, 3, 8),/* enum E __attribute__((packed)) n; */
+		/* } */
+		BTF_END_RAW,
+	},
+	.str_sec = "\0E\0E0\0E1\0A\0m\0n",
+	.str_sec_size = sizeof("\0E\0E0\0E1\0A\0m\0n"),
+	.map_type = BPF_MAP_TYPE_ARRAY,
+	.map_name = "size_check5_map",
+	.key_size = sizeof(int),
+	.value_size = 2,
+	.key_type_id = 1,
+	.value_type_id = 4,
+	.max_entries = 4,
+},
+
 /* typedef const void * const_void_ptr;
  * struct A {
  *	const_void_ptr m;