alloc_guarded_buf
data1_buf = alloc_guarded_buf(test, max_data_len);
data2_buf = alloc_guarded_buf(test, max_data_len);
hash1 = alloc_guarded_buf(test, SHA256_DIGEST_SIZE);
hash2 = alloc_guarded_buf(test, SHA256_DIGEST_SIZE);
ctx = alloc_guarded_buf(test, sizeof(*ctx));