Protect the kernel version space from redefinition.

vboot_firmware/include/rollback_index.h

 /* 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.
  *
  * Functions for querying, manipulating and locking rollback indices
  * stored in the TPM NVRAM.
  */
 
 #ifndef VBOOT_REFERENCE_ROLLBACK_INDEX_H_
 #define VBOOT_REFERENCE_ROLLBACK_INDEX_H_
 
 #include <stdint.h>
 
 extern uint16_t g_firmware_key_version;
 extern uint16_t g_firmware_version;
 extern uint16_t g_kernel_key_version;
 extern uint16_t g_kernel_version;
 
 /* Rollback version types. */
 #define FIRMWARE_VERSIONS 0
 #define KERNEL_VERSIONS   1
 
 /* TPM NVRAM location indices. */
 #define FIRMWARE_VERSIONS_NV_INDEX      0x1001
 #define KERNEL_VERSIONS_NV_INDEX        0x1002
 #define TPM_IS_INITIALIZED_NV_INDEX     0x1003
 #define KERNEL_VERSIONS_BACKUP_NV_INDEX 0x1004
-#define KERNEL_BACKUP_IS_VALID_NV_INDEX 0x1005
+#define KERNEL_MUST_USE_BACKUP_NV_INDEX 0x1005
+
+/* Unique ID to detect kernel space redefinition */
+#define KERNEL_SPACE_UID "GRWL"        /* unique ID with secret meaning */
+#define KERNEL_SPACE_UID_SIZE (sizeof(KERNEL_SPACE_UID) - 1)
+#define KERNEL_SPACE_INIT_DATA ((uint8_t*) "\0\0\0\0" KERNEL_SPACE_UID)
+#define KERNEL_SPACE_SIZE (sizeof(uint32_t) + KERNEL_SPACE_UID_SIZE)
 
 /* All functions return 0 if successful, non-zero if error */
 uint32_t SetupTPM(void);
 uint32_t GetStoredVersions(int type, uint16_t* key_version, uint16_t* version);
 uint32_t WriteStoredVersions(int type, uint16_t key_version, uint16_t version);
 uint32_t LockFirmwareVersions(void);
 uint32_t LockKernelVersionsByLockingPP(void);
 
 #endif  /* VBOOT_REFERENCE_ROLLBACK_INDEX_H_ */