How to pass a structure pointer of a recursive structure between Enclave and Untrust memory

[wwfbear789]

Dear All,

I am trying to pass a recursive structure to Untrust memory with Ocall. However, when I try to access the next member of the structure, I get a Segmentation Fault.
What should I do to correctly pass the structure of the recursive structure? I would like to know if anyone can help me.

In the sample below, the process transits to the Enclave with ecall_enter(), creates an instance of the recursive structure there, and passes it to the Untrust area with ocall_struct_test_func4.

recursive structure in edl (OcallClassTest4)

struct OcallStructTest4 {
        [size=100] char* ident;
        struct OcallStructTest4* next;
};

ecall_enter

void ecall_enter() {
    OcallStructTest4* ocall_struct_test4 = new OcallStructTest4();
    ocall_struct_test4->ident            = "hello struct!";
    ocall_struct_test4->next             = new OcallStructTest4();
    OcallStructTest4* next               = ocall_struct_test4->next;
    next->ident                          = "hello next!!!";
    ocall_struct_test_func4(ocall_struct_test4);
}

 ocall_struct_test_func4

void ocall_struct_test_func4(OcallStructTest4* ocall_struct_test4) {
    std::cout << "ocall struct test func4 start.\n";
    std::cout << ocall_struct_test4->ident << std::endl;

    OcallStructTest4* next = ocall_struct_test4->next;
    std::cout << "next ident" << next->ident << std::endl;
}

ocall definition in edl

void ocall_struct_test_func4([in] struct OcallStructTest4* ocall_struct_test);

Execution result

ocall struct test func4 start.
hello struct!
Segmentation fault

[Sahira_Intel]

Hi,

You might need to increase heap size. Seg fault usually means there is not enough memory allocated to the enclave

Can you please send over your enclave config file so I can take a look.

Sincerely,

Sahira

[wwfbear789]

Thanks for the reply!
The config file for Enclave is below (the application I am currently making is based on SampleEnclave from SampleCode, and the config file has not been changed).

Enclave.config.xml

<EnclaveConfiguration>
  <ProdID>0</ProdID>
  <ISVSVN>0</ISVSVN>
  <StackMaxSize>0x40000</StackMaxSize>
  <HeapMaxSize>0x100000</HeapMaxSize>
  <TCSNum>10</TCSNum>
  <TCSPolicy>1</TCSPolicy>
  <!-- Recommend changing 'DisableDebug' to 1 to make the enclave undebuggable for enclave release -->
  <DisableDebug>0</DisableDebug>
  <MiscSelect>0</MiscSelect>
  <MiscMask>0xFFFFFFFF</MiscMask>
</EnclaveConfiguration>

Also, I have a question, is it not possible to access the next referenced data just by passing the pointer of the self-reference structure from the Enclave to the Untrust area (or vice versa)?
Currently I am not able to do that, so I am using a technique such as passing a uint8_t* converted to a byte string. Is there another smarter way?

[Sahira_Intel]

Hi,

I have escalated this issue further. I will let you know when I have more information. 

Sincerely,

Sahira 

[wwfbear789]

Thanks for the reply!

I am sorry for the trouble. I look forward to hearing back from you.

Sincerely

wwfbear789

[Sahira_Intel · Accepted solution]

Hi,

No trouble at all.

In the SGX Developer Guide, there is a section on Structure Deep Copy: https://download.01.org/intel-sgx/latest/linux-latest/docs/Intel_SGX_Developer_Reference_Linux_2.17_Open_Source.pdf#page=56

There is a sample there that you can follow that might help

Sincerely,

Sahira