UEFI TGC2's sendCommand always returns error 21

Question

I'm developing an UEFI app using the TPM2. getCapabilities works, but everything else is shoved onto this submitCommand() function. everything I try there returns EFI_ABORTED as status.

I tried several commands, like read_PCR and get_random_number, but it appears to occur for all commands (TPM2 spec part 3). I chose the random number command because it's a simple command without authorization or encryption that should always return when executed correctly.

struct TPM2_ {
    EFI_HANDLE image;
    EFI_BOOT_SERVICES *BS;
    EFI_TCG2_PROTOCOL *prot;
    UINT32 activePCRbanks;
};

struct TPM2_Rand_Read_Command {
        TPMI_ST_COMMAND_TAG     tag;
        UINT32                  commandSize;
        TPM_CC                  commandCode;
        UINT16                  bytesRequested;
    };
    struct TPM2_Rand_Read_Response {
        TPM_ST                  tag;
        UINT32                  responseSize;
        TPM_RC                  responseCode;
        TPM2B_DIGEST            randomBytes;
    };

UINTN tpm_get_random(TPM2 * tpm) {
    struct TPM2_Rand_Read_Command cmd;
    struct TPM2_Rand_Read_Response resp;

    cmd.tag = __builtin_bswap16(TPM_ST_NO_SESSIONS); //x86 is little endian, TPM2 is big-endian, use bswap to convert!)
    cmd.commandCode = __builtin_bswap32(TPM_CC_GetRandom);
    cmd.commandSize = __builtin_bswap32(sizeof(struct TPM2_Rand_Read_Command));
    cmd.bytesRequested = __builtin_bswap16(4);
    EFI_STATUS stat = tpm->prot->SubmitCommand(tpm->prot,sizeof(struct TPM2_Rand_Read_Command), (UINT8*)&cmd,sizeof(struct TPM2_Rand_Read_Response),(UINT8*)&resp); //responds 0x15 || 21
    Print(L"statreadrand: %x \t %d \r\n", stat, *((UINT32*)resp.randomBytes.buffer));
    CHECK_STATUS(stat, L"SubmitReadCommand");
    return 0;
}

TPM2* tpm_create(EFI_BOOT_SERVICES *BS, EFI_HANDLE image) {
    TPM2* tpm = calloc(1, sizeof(TPM2));
    EFI_GUID prot_guid = (EFI_GUID)EFI_TCG2_PROTOCOL_GUID;
    tpm->BS = BS;
    tpm->image = image;
    EFI_STATUS stat = tpm->BS->LocateProtocol(&prot_guid, NULL, (void **)&tpm->prot);
    CHECK_STATUS(stat, L"LocateTPMProtocol");
    return tpm;
}

I expect the SubmitCommand function to return EFI_SUCCESS (0) and fill the response struct with 4 random bytes. But the function returns EFI_ABORTED (21)

Does anyone know how to solve this?

EDIT: tried different toolchains (GNU-EFI/ plain GCC / EDK2) all give the same behaviour.

Answer 1

The particular PC had this exact problem. probably the TPM was locked. When using a different PC With a TPM2 the problem didn' t occur and instead, I just got a random number back.