Proper way to free all data in spdm_context

[steven-bellock]

Discussed in DMTF/libspdm#2320

^{Originally posted by LeeTroy August 22, 2023}
I'm running libspdm in a embedded project, the spdm context will be created and released over and over again.
However, I found there's no proper way to release some of data within context.

spdm-emu/spdm_emu/spdm_requester_emu/spdm_requester_spdm.c

Lines 454 to 467 in 3630f47

	res = libspdm_read_responder_root_public_certificate(m_use_hash_algo,
	m_use_asym_algo,
	&data, &data_size,
	&hash, &hash_size);
	if (res) {
	libspdm_x509_get_cert_from_cert_chain(
	(uint8_t *)data + sizeof(spdm_cert_chain_t) + hash_size,
	data_size - sizeof(spdm_cert_chain_t) - hash_size, 0,
	&root_cert, &root_cert_size);
	libspdm_zero_mem(&parameter, sizeof(parameter));
	parameter.location = LIBSPDM_DATA_LOCATION_LOCAL;
	libspdm_set_data(spdm_context,
	LIBSPDM_DATA_PEER_PUBLIC_ROOT_CERT,
	&parameter, (void *)root_cert, root_cert_size);

res = libspdm_read_responder_root_public_certificate(m_use_hash_algo,
                                                     m_use_asym_algo,
                                                     &data, &data_size,
                                                     &hash, &hash_size);
if (res) {
    libspdm_x509_get_cert_from_cert_chain(
        (uint8_t *)data + sizeof(spdm_cert_chain_t) + hash_size,
        data_size - sizeof(spdm_cert_chain_t) - hash_size, 0,
        &root_cert, &root_cert_size);
    libspdm_zero_mem(&parameter, sizeof(parameter));
    parameter.location = LIBSPDM_DATA_LOCATION_LOCAL;
    libspdm_set_data(spdm_context,
                     LIBSPDM_DATA_PEER_PUBLIC_ROOT_CERT,
                     &parameter, (void *)root_cert, root_cert_size);
}

• libspdm_read_responder_root_public_certificate allocates data
• data can't be release because root_cert sit inside data
• libspdm_get_data doesn't support LIBSPDM_DATA_PEER_PUBLIC_ROOT_CERT, even if it is supported, the pointer is root_cert but not data.

One solution I can think of storing data pointer with LIBSPDM_DATA_APP_CONTEXT_DATA, and release it when the spdm context is not needed.

Thanks!

[jyao1]

I think the integrator (spdm-emu) can free those data instead of libspdm.

The reason is that libspdm does not has any alloc/free function. libspdm has no knowledge on if the data is in heap or global variable.