Pay attention to TPM communication errors

firmware/stub/tpm_lite_stub.c

 /* Copyright (c) 2010 The Chromium OS Authors. All rights reserved.
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  *
  * Stub implementations of utility functions which call their linux-specific
  * equivalents.
  */
 
 #define _STUB_IMPLEMENTATION_
 #include "tlcl.h"
@@ skipping 111 matching lines @@
     device_path = TPM_DEVICE_PATH;
   }
 
   tpm_fd = open(device_path, O_RDWR);
   if (tpm_fd < 0) {
     error("cannot open TPM device %s: %s\n", device_path, strerror(errno));
   }
 }
 
 
-void TlclStubSendReceive(uint8_t* request, int request_length,
-                         uint8_t* response, int max_length) {
+uint32_t TlclStubSendReceive(uint8_t* request, int request_length,
+                             uint8_t* response, int max_length) {
   /*
    * In a real firmware implementation, this function should contain
    * the equivalent API call for the firmware TPM driver which takes a
    * raw sequence of bytes as input command and a pointer to the
    * output buffer for putting in the results.
    *
    * For EFI firmwares, this can make use of the EFI TPM driver as
    * follows (based on page 16, of TCG EFI Protocol Specs Version 1.20
    * availaible from the TCG website):
    *
@@ skipping 32 matching lines @@
   tag = TpmTag(request);
   response_tag = TpmTag(response);
   assert(
     (tag == TPM_TAG_RQU_COMMAND &&
      response_tag == TPM_TAG_RSP_COMMAND) ||
     (tag == TPM_TAG_RQU_AUTH1_COMMAND &&
      response_tag == TPM_TAG_RSP_AUTH1_COMMAND) ||
     (tag == TPM_TAG_RQU_AUTH2_COMMAND &&
      response_tag == TPM_TAG_RSP_AUTH2_COMMAND));
   assert(response_length == TpmResponseSize(response));
+
+  return 0;  /* Success */
 }