Pay attention to TPM communication errors

firmware/lib/tpm_lite/tlcl.c

Index: firmware/lib/tpm_lite/tlcl.c
diff --git a/firmware/lib/tpm_lite/tlcl.c b/firmware/lib/tpm_lite/tlcl.c
index 21966457f09237d7c2c58312840fd460087ba547..94a282863a55414f3a6fa6ca5eb2409ac80c87e3 100644
--- a/firmware/lib/tpm_lite/tlcl.c
+++ b/firmware/lib/tpm_lite/tlcl.c
@@ -45,21 +45,12 @@ static INLINE int TpmReturnCode(const uint8_t* buffer) {
   return TpmCommandCode(buffer);
 }
 
-/* Checks for errors in a TPM response. */
-static void CheckResult(uint8_t* request, uint8_t* response, int warn_only) {
-  int command = TpmCommandCode(request);
-  int result = TpmReturnCode(response);
-  if (result != TPM_SUCCESS) {
-    if (warn_only)
-      VBDEBUG(("TPM: command 0x%x failed: 0x%x\n", command, result));
-    else
-      error("TPM: command 0x%x failed: 0x%x\n", command, result);
-  }
-}
+/* Sends a TPM command and gets a response.  Returns 0 if success or the TPM
+ * error code if error. */
+static uint32_t TlclSendReceive(uint8_t* request, uint8_t* response,
+                                int max_length) {
 
-/* Sends a TPM command and gets a response. */
-static void TlclSendReceive(uint8_t* request, uint8_t* response,
-                            int max_length) {
+  uint32_t result;
 
 #ifdef EXTRA_LOGGING
   VBDEBUG(("TPM: command: %x%x %x%x%x%x %x%x%x%x\n",
@@ -68,8 +59,16 @@ static void TlclSendReceive(uint8_t* request, uint8_t* response,
            request[6], request[7], request[8], request[9]));
 #endif
 
-  TlclStubSendReceive(request, TpmCommandSize(request),
-                      response, max_length);
+  result = TlclStubSendReceive(request, TpmCommandSize(request),
+                               response, max_length);
+  if (0 != result) {
+    /* Communication with TPM failed, so response is garbage */
+    VBDEBUG(("TPM: command 0x%x send/receive failed: 0x%x\n",
+             TpmCommandCode(request), result));
+    return TPM_E_COMMUNICATION_ERROR;
+  }
+  /* Otherwise, use the result code from the response */
+  result = TpmReturnCode(response);
 
 #ifdef EXTRA_LOGGING
   VBDEBUG(("TPM: response: %x%x %x%x%x%x %x%x%x%x\n",
@@ -78,21 +77,17 @@ static void TlclSendReceive(uint8_t* request, uint8_t* response,
            response[6], response[7], response[8], response[9]));
 #endif
 
-#ifdef VBOOT_DEBUG
-  {
-    int command = TpmCommandCode(request);
-    int result = TpmReturnCode(response);
-    VBDEBUG(("TPM: command 0x%x returned 0x%x\n", command, result));
-  }
-#endif
+  VBDEBUG(("TPM: command 0x%x returned 0x%x\n",
+           TpmCommandCode(request), result));
+
+  return result;
 }
 
 
 /* Sends a command and returns the error code. */
 static uint32_t Send(uint8_t* command) {
   uint8_t response[TPM_LARGE_ENOUGH_COMMAND_SIZE];
-  TlclSendReceive(command, response, sizeof(response));
-  return TpmReturnCode(response);
+  return TlclSendReceive(command, response, sizeof(response));
 }
 
 /* Exported functions. */
@@ -141,10 +136,7 @@ uint32_t TlclWrite(uint32_t index, uint8_t* data, uint32_t length) {
   ToTpmUint32(cmd.buffer + tpm_nv_write_cmd.length, length);
   Memcpy(cmd.buffer + tpm_nv_write_cmd.data, data, length);
 
-  TlclSendReceive(cmd.buffer, response, sizeof(response));
-  CheckResult(cmd.buffer, response, 1);
-
-  return TpmReturnCode(response);
+  return TlclSendReceive(cmd.buffer, response, sizeof(response));
 }
 
 uint32_t TlclRead(uint32_t index, uint8_t* data, uint32_t length) {
@@ -158,8 +150,7 @@ uint32_t TlclRead(uint32_t index, uint8_t* data, uint32_t length) {
   ToTpmUint32(cmd.buffer + tpm_nv_read_cmd.index, index);
   ToTpmUint32(cmd.buffer + tpm_nv_read_cmd.length, length);
 
-  TlclSendReceive(cmd.buffer, response, sizeof(response));
-  result = TpmReturnCode(response);
+  result = TlclSendReceive(cmd.buffer, response, sizeof(response));
   if (result == TPM_SUCCESS && length > 0) {
     uint8_t* nv_read_cursor = response + kTpmResponseHeaderLength;
     FromTpmUint32(nv_read_cursor, &result_length);
@@ -187,8 +178,7 @@ uint32_t TlclAssertPhysicalPresence(void) {
 
 uint32_t TlclAssertPhysicalPresenceResult(void) {
   uint8_t response[TPM_LARGE_ENOUGH_COMMAND_SIZE];
-  TlclSendReceive(tpm_ppassert_cmd.buffer, response, sizeof(response));
-  return TpmReturnCode(response);
+  return TlclSendReceive(tpm_ppassert_cmd.buffer, response, sizeof(response));
 }
 
 uint32_t TlclLockPhysicalPresence(void) {
@@ -204,8 +194,7 @@ uint32_t TlclSetNvLocked(void) {
 int TlclIsOwned(void) {
   uint8_t response[TPM_LARGE_ENOUGH_COMMAND_SIZE + TPM_PUBEK_SIZE];
   uint32_t result;
-  TlclSendReceive(tpm_readpubek_cmd.buffer, response, sizeof(response));
-  result = TpmReturnCode(response);
+  result = TlclSendReceive(tpm_readpubek_cmd.buffer, response, sizeof(response));
   return (result != TPM_SUCCESS);
 }
 
@@ -239,11 +228,10 @@ uint32_t TlclGetFlags(uint8_t* disable, uint8_t* deactivated, uint8_t *nvlocked)
   uint32_t size;
   VBDEBUG(("TPM: Get flags\n"));
 
-  TlclSendReceive(tpm_getflags_cmd.buffer, response, sizeof(response));
-  result = TpmReturnCode(response);
-  if (result != TPM_SUCCESS) {
+  result = TlclSendReceive(tpm_getflags_cmd.buffer, response, sizeof(response));
+  if (result != TPM_SUCCESS)
     return result;
-  }
+
   FromTpmUint32(response + kTpmResponseHeaderLength, &size);
   assert(size == sizeof(TPM_PERMANENT_FLAGS));
   pflags =
@@ -261,20 +249,25 @@ uint32_t TlclGetFlags(uint8_t* disable, uint8_t* deactivated, uint8_t *nvlocked)
 
 uint32_t TlclSetGlobalLock(void) {
   uint32_t x;
-  VBDEBUG(("TPM: Set Set global lock\n"));
+  VBDEBUG(("TPM: Set global lock\n"));
   return TlclWrite(TPM_NV_INDEX0, (uint8_t*) &x, 0);
 }
 
 uint32_t TlclExtend(int pcr_num, uint8_t* in_digest, uint8_t* out_digest) {
   struct s_tpm_extend_cmd cmd;
   uint8_t response[kTpmResponseHeaderLength + kPcrDigestLength];
+  uint32_t result;
 
   Memcpy(&cmd, &tpm_extend_cmd, sizeof(cmd));
   ToTpmUint32(cmd.buffer + tpm_extend_cmd.pcrNum, pcr_num);
   Memcpy(cmd.buffer + cmd.inDigest, in_digest, kPcrDigestLength);
-  TlclSendReceive(cmd.buffer, response, sizeof(response));
+
+  result = TlclSendReceive(cmd.buffer, response, sizeof(response));
+  if (result != TPM_SUCCESS)
+    return result;
+
   Memcpy(out_digest, response + kTpmResponseHeaderLength, kPcrDigestLength);
-  return TpmReturnCode(response);
+  return result;
 }
 
 uint32_t TlclGetPermissions(uint32_t index, uint32_t* permissions) {
@@ -286,11 +279,10 @@ uint32_t TlclGetPermissions(uint32_t index, uint32_t* permissions) {
 
   Memcpy(&cmd, &tpm_getpermissions_cmd, sizeof(cmd));
   ToTpmUint32(cmd.buffer + tpm_getpermissions_cmd.index, index);
-  TlclSendReceive(cmd.buffer, response, sizeof(response));
-  result = TpmReturnCode(response);
-  if (result != TPM_SUCCESS) {
+  result = TlclSendReceive(cmd.buffer, response, sizeof(response));
+  if (result != TPM_SUCCESS)
     return result;
-  }
+
   nvdata = response + kTpmResponseHeaderLength + sizeof(size);
   FromTpmUint32(nvdata + kNvDataPublicPermissionsOffset, permissions);
   return result;