CWE-1233: Security-Sensitive Hardware Controls with Missing Lock Bit Protection
Description
The product uses a register lock bit protection mechanism, but it does not ensure that the lock bit prevents modification of system registers or controls that perform changes to important hardware system configuration.
Submission Date :
Jan. 15, 2020, midnight
Modification Date :
2023-06-29 00:00:00+00:00
Organization :
Intel Corporation
Extended Description
Integrated circuits and hardware intellectual properties (IPs) might provide device configuration controls that need to be programmed after device power reset by a trusted firmware or software module, commonly set by BIOS/bootloader. After reset, there can be an expectation that the controls cannot be used to perform any further modification. This behavior is commonly implemented using a trusted lock bit, which can be set to disable writes to a protected set of registers or address regions. The lock protection is intended to prevent modification of certain system configuration (e.g., memory/memory protection unit configuration).
However, if the lock bit does not effectively write-protect all system registers or controls that could modify the protected system configuration, then an adversary may be able to use software to access the registers/controls and modify the protected hardware configuration.
Example - 1
Consider the example design below for a digital thermal sensor that detects overheating of the silicon and triggers system shutdown. The system critical temperature limit (CRITICAL_TEMP_LIMIT) and thermal sensor calibration (TEMP_SENSOR_CALIB) data have to be programmed by the firmware.
<xhtml_table><xhtml_tr><xhtml_th>Register</xhtml_th><xhtml_th>Field description</xhtml_th></xhtml_tr><xhtml_tr><xhtml_td>CRITICAL_TEMP_LIMIT</xhtml_td><xhtml_td>
[31:8] Reserved field; Read only; Default 0[7:0] Critical temp 0-255 Centigrade; Read-write-lock; Default 125</xhtml_td></xhtml_tr><xhtml_tr><xhtml_td>TEMP_SENSOR_CALIB</xhtml_td><xhtml_td>[31:0] Thermal sensor calibration data. A slope value used to map sensor reading to a degree Centigrade. Read-write; Default 25</xhtml_td></xhtml_tr><xhtml_tr><xhtml_td>TEMP_SENSOR_LOCK</xhtml_td><xhtml_td>
[31:1] Reserved field; Read only; Default 0[0] Lock bit, locks CRITICAL_TEMP_LIMIT register; Write-1-once; Default 0</xhtml_td></xhtml_tr><xhtml_tr><xhtml_td>TEMP_HW_SHUTDOWN</xhtml_td><xhtml_td>
[31:2] Reserved field; Read only; Default 0[1] Enable hardware shutdown on a critical temperature detection; Read-write; Default 0</xhtml_td></xhtml_tr><xhtml_tr><xhtml_td>CURRENT_TEMP</xhtml_td><xhtml_td>
[31:8] Reserved field; Read only; Default 0[7:0] Current Temp 0-255 Centigrade; Read-only; Default 0 </xhtml_td></xhtml_tr></xhtml_table>
<xhtml_p>Change TEMP_HW_SHUTDOWN and TEMP_SENSOR_CALIB controls to be locked by TEMP_SENSOR_LOCK.</xhtml_p><xhtml_table><xhtml_tr><xhtml_td>TEMP_SENSOR_CALIB</xhtml_td><xhtml_td>[31:0] Thermal sensor calibration data. A slope value used to map sensor reading to a degree Centigrade. Read-write-Lock; Default 25; Locked by TEMP_SENSOR_LOCK bit[0]</xhtml_td></xhtml_tr><xhtml_tr><xhtml_td>TEMP_HW_SHUTDOWN</xhtml_td><xhtml_td><xhtml_p></xhtml_p>[31:2] Reserved field; Read only; Default 0[1] Enable hardware shutdown on critical temperature detection; Read-write-Lock; Default 0; Locked by TEMP_SENSOR_LOCK bit[0]</xhtml_td></xhtml_tr></xhtml_table>
Related Weaknesses
This table shows the weaknesses and high level categories that are related to this weakness. These relationships are defined to give an overview of the different insight to similar items that may exist at higher and lower levels of abstraction.
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