CWE-1224 Detail

The hardware design control register "sticky bits" or write-once bit fields are improperly implemented, such that they can be reprogrammed by software.

Integrated circuits and hardware IP software programmable controls and settings are commonly stored in register circuits. These register contents have to be initialized at hardware reset to define default values that are hard coded in the hardware description language (HDL) code of the hardware unit. A common security protection method used to protect register settings from modification by software is to make the settings write-once or "sticky." This allows writing to such registers only once, whereupon they become read-only. This is useful to allow initial boot software to configure systems settings to secure values while blocking runtime software from modifying such hardware settings.

Failure to implement write-once restrictions in hardware design can expose such registers to being re-programmed by software and written multiple times. For example, write-once fields could be implemented to only be write-protected if they have been set to value "1", wherein they would work as "write-1-once" and not "write-once".

Modes Of Introduction

Architecture and Design
Implementation : Such issues could be introduced during implementation of hardware design, since IP parameters and defaults are defined in HDL code and identified later during Testing or System Configuration phases.

Applicable Platforms

Language

Name: Verilog (Undetermined)
Name: VHDL (Undetermined)

Technologies

Class: System on Chip (Undetermined)

Common Consequences

Potential Mitigations

Phases : Architecture and Design
During hardware design all register write-once or sticky fields must be evaluated for proper configuration.
Phases : Testing
The testing phase should use automated tools to test that values are not reprogrammable and that write-once fields lock on writing zeros.

Vulnerability Mapping Notes

Justification : This CWE entry is at the Base level of abstraction, which is a preferred level of abstraction for mapping to the root causes of vulnerabilities.
Comment : Carefully read both the name and description to ensure that this mapping is an appropriate fit. Do not try to 'force' a mapping to a lower-level Base/Variant simply to comply with this preferred level of abstraction.

Related Attack Patterns

Submission

Modifications