Improper Implementation of Lock Protection Registers
The product incorrectly implements register lock bit protection features such that protected controls can be programmed even after the lock has been set.
In integrated circuits and hardware IPs, device configuration controls are commonly programmed after a device power reset by a trusted firmware or software module (e.g., BIOS/bootloader) and then locked from any further modification. This is commonly implemented using a trusted lock bit, which when set disables writes to a protected set of registers or address regions. Design or coding errors in the implementation of the lock bit protection feature may allow the lock bit to be modified or cleared by software after being set to unlock the system.
The following examples help to illustrate the nature of this weakness and describe methods or techniques which can be used to mitigate the risk.
Note that the examples here are by no means exhaustive and any given weakness may have many subtle varieties, each of which may require different detection methods or runtime controls.
Consider the example design below or a digital thermal sensor used in the design to detect overheating of the silicon and trigger system shutdown. The system critical temperature limit (CRITICAL_TEMP_LIMIT) and thermal sensor calibration (TEMP_SENSOR_CALIB) data have to be programmed by firmware and then the register needs to be locked (TEMP_SENSOR_LOCK).
In this example note that the response of the system if the system heats to critical temperature is controlled by TEMP_HW_SHUTDOWN bit , which is not lockable. Thus, the intended security property of the critical temperature sensor cannot be fully protected,since software can misconfigure the TEMP_HW_SHUTDOWN register even after the lock bit is set to disable the shutdown response.
Weaknesses in this category are related to hardware-circuit design and logic (e.g., CMOS transistors, finite state machines, and registers) as well as issues related t...
This view (slice) covers all the elements in CWE.
CWE identifiers in this view are weaknesses that do not have associated Software Fault Patterns (SFPs), as covered by the CWE-888 view. As such, they represent gaps in...
This view (slice) lists weaknesses that can be introduced during implementation.