Untrusted agents can disable alerts about signal conditions exceeding limits or the response mechanism that handles such alerts.
Hardware sensors are used to detect whether a device is operating within design limits. The threshold values for these limits are set by hardware fuses or trusted software such as a BIOS. Modification of these limits may be protected by hardware mechanisms. When device sensors detect out of bound conditions, alert signals may be generated for remedial action, which may take the form of device shutdown or throttling. Warning signals that are not properly secured may be disabled or used to generate spurious alerts, causing degraded performance or denial-of-service (DoS). These alerts may be masked by untrusted software. Examples of these alerts involve thermal and power sensor alerts.
Threat Mapped score: 1.5
Industry: Finiancial
Threat priority: P4 - Informational (Low)
| Phase | Note |
|---|---|
| Architecture and Design | N/A |
| Implementation | N/A |
Intro: Consider a platform design where a Digital-Thermal Sensor (DTS) is used to monitor temperature and compare that output against a threshold value. If the temperature output equals or exceeds the threshold value, the DTS unit sends an alert signal to the processor. The processor, upon getting the alert, input triggers system shutdown. The alert signal is handled as a General-Purpose-I/O (GPIO) pin in input mode.
Body: Reprogramming the state of the GPIO pin allows malicious software to trigger spurious alerts or to set the alert pin to a zero value so that thermal sensor alerts are not received by the processor.
The processor-GPIO controller exposes software-programmable controls that allow untrusted software to reprogram the state of the GPIO pin.