Tolerate lack of TPM reset in common cases.

This is a temporary workaround for Tegra boards that don't reset the TPM
when the CPU is reset.  It makes the firmware more lenient when execution
starts with an already locked TPM.

BUG=chromeos-partner:3574
TEST=none (yet)

Change-Id: If6a060595c1eb41e95e0935f8467de8bb6256b12
Reviewed-on: http://gerrit.chromium.org/gerrit/1429
Reviewed-by: Gaurav Shah <gauravsh@chromium.org>
Reviewed-by: Randall Spangler <rspangler@chromium.org>
Tested-by: Nick Sanders <nsanders@chromium.org>

firmware/arch/arm/include/biosincludes.h

@@ -43,4 +43,9 @@ extern void debug(const char *format, ...);
 #define UINT64_MAX (UINT64_C(0xffffffffffffffffULL))
 #endif
 
+/* This workaround applies to Kaen prototypes and is not expected to be needed
+ * in the final products.  See crosbug.com/15759.
+ */
+#define TEGRA_SOFT_REBOOT_WORKAROUND
+
 #endif /*__ARCH_ARM_BIOSINCLUDES_H__ */

firmware/lib/rollback_index.c

@@ -15,6 +15,10 @@
 
 static int g_rollback_recovery_mode = 0;
 
+#ifdef TEGRA_SOFT_REBOOT_WORKAROUND
+static int soft_reset = 0;
+#endif
+
 /* disable MSVC warning on const logical expression (as in } while(0);) */
 __pragma(warning (disable: 4127))
 
@@ -47,6 +51,21 @@ static uint32_t SafeWrite(uint32_t index, const void* data, uint32_t length) {
   if (result == TPM_E_MAXNVWRITES) {
     RETURN_ON_FAILURE(TPMClearAndReenable());
     return TlclWrite(index, data, length);
+#ifdef TEGRA_SOFT_REBOOT_WORKAROUND
+  } else if ((result == TPM_E_BAD_PRESENCE ||
+              result == TPM_E_AREA_LOCKED) &&
+             soft_reset == 1) {
+    /* Ignore writes that failed because the TPM wasn't unlocked.
+     *
+     * This may have security implications.  1. It may delay updating the
+     * version number, therefore widening the window for a rollback attack.
+     * 2. It may prevent noticing transitions between developer mode and normal
+     * mode, in which case the TPM owner will not be cleared when
+     * transitioning.  See crosbug.com/15759.  Note that this code path is not
+     * taken on systems where a CPU reset implies a TPM reset.
+     */
+    return TPM_SUCCESS;
+#endif
   } else {
     return result;
   }
@@ -190,7 +209,22 @@ uint32_t SetupTPM(int recovery_mode, int developer_mode,
 
   RETURN_ON_FAILURE(TlclLibInit());
 
+#ifdef TEGRA_SOFT_REBOOT_WORKAROUND
+  result = TlclStartup();
+  if (result == TPM_E_INVALID_POSTINIT) {
+    /* Some prototype hardware doesn't reset the TPM on a CPU reset.  We try to
+     * tolerate this failure, which is possible in most cases.
+     */
+    VBDEBUG(("TPM: soft reset detected\n", result));
+    soft_reset = 1;
+  } else if (result != TPM_SUCCESS) {
+    VBDEBUG(("TPM: TlclStartup returned %08x\n", result));
+    return result;
+  }
+#else
   RETURN_ON_FAILURE(TlclStartup());
+#endif
+
   /* Some TPMs start the self test automatically at power on.  In that case we
    * don't need to call ContinueSelfTest.  On some (other) TPMs,
    * ContinueSelfTest may block.  In that case, we definitely don't want to
@@ -210,7 +244,20 @@ uint32_t SetupTPM(int recovery_mode, int developer_mode,
   RETURN_ON_FAILURE(TlclContinueSelfTest());
 #endif
   result = TlclAssertPhysicalPresence();
-  if (result != 0) {
+#ifdef TEGRA_SOFT_REBOOT_WORKAROUND
+    /*
+     * If soft_reset is true, the failure to assert PP is expected because the
+     * TPM is locked from a previous boot.  In this case we will never execute
+     * the PhysicalPresenceCMDEnable below, but that's OK because this is a
+     * warm boot and at some point in the past we must have cold-booted with
+     * this firmware (one would hope), so that situation (TPM delivered with PP
+     * disabled) has already been resolved.
+     */
+  if (soft_reset) {
+    result = TPM_SUCCESS;
+  }
+#endif
+  if (result != TPM_SUCCESS) {
     /* It is possible that the TPM was delivered with the physical presence
      * command disabled.  This tries enabling it, then tries asserting PP
      * again.
@@ -437,7 +484,18 @@ uint32_t RollbackKernelLock(void) {
   if (g_rollback_recovery_mode) {
     return TPM_SUCCESS;
   } else {
+#ifdef TEGRA_SOFT_REBOOT_WORKAROUND
+    TPM_STCLEAR_FLAGS flags;
+    uint32_t result = TlclLockPhysicalPresence();
+    if (result == TPM_SUCCESS) {
+      return result;
+    }
+    RETURN_ON_FAILURE(TlclGetSTClearFlags(&flags));
+    /* Ignore PP locking failure if PP is already locked. */
+    return flags.physicalPresenceLock == 1 ? TPM_SUCCESS : result;
+#else
     return TlclLockPhysicalPresence();
+#endif
   }
 }