Missing Write Protection for Parametric Data Values
The device does not write-protect the parametric data values for sensors that scale the sensor value, allowing untrusted software to manipulate the apparent result and potentially damage hardware or cause operational failure.
Various sensors are used by hardware to detect any devices operating outside of the design limits. The threshold limit values are set by hardware fuses or trusted software such as the BIOS. These limits may be related to thermal, power, voltage, current, and frequency. Hardware mechanisms may be used to protect against alteration of the threshold limit values by untrusted software. The limit values are generally programmed in standard units for the type of value being read. However, the hardware-sensor blocks may report the settings in different units depending upon sensor design and operation. The raw sensor output value is converted to the desired units using a scale conversion based on the parametric data programmed into the sensor. The final converted value is then compared with the previously programmed limits. While the limit values are usually protected, the sensor parametric data values may not be. By changing the parametric data, safe operational limits may be bypassed.
Impact: Quality DegradationDoS: Resource Consumption (Other)
Sensor value manipulation, particularly thermal or power, may allow physical damage to occur or disabling of the device by a false fault shutdown causing a Denial-Of-Service.
Effectiveness: High
Code Example:
The sensor frequency value is scaled by applying the function:
otherwhere a and b are the programmable calibration data coefficients. Software sets a and b to zero ensuring the sensed temperature is always zero.
Code Example:
The sensor frequency value is scaled by applying the function:
otherwhere a and b are the programmable calibration data coefficients. Untrusted software is prevented from changing the values of either a or b, preventing this method of manipulating the temperature.