bpf: fix BTF verification of enums

vmlinux BTF has enums that are 8 byte and 1 byte in size.
2 byte enum is a valid construct as well.
Fix BTF enum verification to accept those sizes.

Fixes: 69b693f0 ("bpf: btf: Introduce BPF Type Format (BTF)")
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>
Acked-by: NMartin KaFai Lau <kafai@fb.com>
Signed-off-by: NDaniel Borkmann <daniel@iogearbox.net>

kernel/bpf/btf.c

@@ -2377,9 +2377,8 @@ static s32 btf_enum_check_meta(struct btf_verifier_env *env,
 		return -EINVAL;
 	}
 
-	if (t->size != sizeof(int)) {
-		btf_verifier_log_type(env, t, "Expected size:%zu",
-				      sizeof(int));
+	if (t->size > 8 || !is_power_of_2(t->size)) {
+		btf_verifier_log_type(env, t, "Unexpected size");
 		return -EINVAL;
 	}