Security-Sensitive Hardware Controls with Missing Lock Bit Protection

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.

Abstraction

Base

Structure

Simple

Likelihood of Exploit

Medium

Understand the problem

What is the problem?

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.

Root cause

How and when does the problem arise?

Lifecycle phase

Architecture and Design

Such issues could be introduced during hardware architecture and design and identified later during Testing or System Configuration phases.

Lifecycle phase

Implementation

Such issues could be introduced during implementation and identified later during Testing or System Configuration phases.

Risk

What does successful exploitation lead to?

Modify Memory

Affected security scopes: Access Control

System Configuration protected by the lock bit can be modified even when the lock is set.

Defence

How is it prevented and fixed?

Architecture and Design · Implementation · Testing

Defence to apply across several lifecycle phases

Detail

- Security lock bit protections must be reviewed for design inconsistency and common weaknesses. - Security lock programming flow and lock properties must be tested in pre-silicon and post-silicon testing.

Verification

How is it detected?

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.