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.

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.

Potential Impact

Demonstrative Examples

Register
				        Field description
				    
				
				  CRITICAL_TEMP_LIMIT
				  
				  [31:8] Reserved field; Read only; Default 0[7:0] Critical temp 0-255 Centigrade; Read-write-lock; Default 125
				  
				  
				  
				  TEMP_SENSOR_CALIB
				  
				  [31:0] Thermal sensor calibration data. A slope value used to map sensor reading to a degree Centigrade. Read-write; Default 25
				  
				  
				  
				  TEMP_SENSOR_LOCK
				  
				  [31:1] Reserved field; Read only; Default 0[0] Lock bit, locks CRITICAL_TEMP_LIMIT register; Write-1-once; Default 0
				  
				  
				  
				  TEMP_HW_SHUTDOWN
				  
				  [31:2] Reserved field; Read only; Default 0[1] Enable hardware shutdown on a critical temperature detection; Read-write; Default 0
				  
				  
				  
				  CURRENT_TEMP
				  
				  [31:8] Reserved field; Read only; Default 0[7:0]   Current Temp 0-255 Centigrade; Read-only; Default 0

Change TEMP_HW_SHUTDOWN and TEMP_SENSOR_CALIB controls to be locked by TEMP_SENSOR_LOCK.
			   
			   
				
				  TEMP_SENSOR_CALIB
				  
				  [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]
				  
				  
				  
				  TEMP_HW_SHUTDOWN
				  
				  [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]

Mitigations & Prevention

Detection Methods

• Manual Analysis High — Set the lock bit. Attempt to modify the information protected by the lock bit. If the information is changed, implement a design fix. Retest. Also, attempt to indirectly clear the lock bit or bypass it.

Real-World CVE Examples

Related Weaknesses