Improperly Preserved Integrity of Hardware Configuration State During a Power Save/Restore Operation

Description

The product performs a power save/restore operation, but it does not ensure that the integrity of the configuration state is maintained and/or verified between the beginning and ending of the operation.

Extended Description

Before powering down, the Intellectual Property (IP) saves current state (S) to persistent storage such as flash or always-on memory in order to optimize the restore operation. During this process, an attacker with access to the persistent storage may alter (S) to a configuration that could potentially modify privileges, disable protections, and/or cause damage to the hardware. If the IP does not validate the configuration state stored in persistent memory, upon regaining power or becoming operational again, the IP could be compromised through the activation of an unwanted/harmful configuration.

Common Consequences 1

Scope: ConfidentialityIntegrity

Impact: DoS: InstabilityDoS: Crash, Exit, or RestartDoS: Resource Consumption (Other)Gain Privileges or Assume IdentityBypass Protection MechanismAlter Execution LogicQuality DegradationUnexpected StateReduce MaintainabilityReduce PerformanceReduce Reliability

Potential Mitigations 3

Phase: Architecture and Design

Inside the IP, incorporate integrity checking on the configuration state via a cryptographic hash. The hash can be protected inside the IP such as by storing it in internal registers which never lose power. Before powering down, the IP performs a hash of the configuration and saves it in these persistent registers. Upon restore, the IP performs a hash of the saved configuration and compares it with the saved hash. If they do not match, then the IP should not trust the configuration.

Phase: Integration

Outside the IP, incorporate integrity checking of the configuration state via a trusted agent. Before powering down, the trusted agent performs a hash of the configuration and saves the hash in persistent storage. Upon restore, the IP requests the trusted agent validate its current configuration. If the configuration hash is invalid, then the IP should not trust the configuration.

Phase: Integration

Outside the IP, incorporate a protected environment that prevents undetected modification of the configuration state by untrusted agents. Before powering down, a trusted agent saves the IP's configuration state in this protected location that only it is privileged to. Upon restore, the trusted agent loads the saved state into the IP.

Demonstrative Examples 1

The following pseudo code demonstrates the power save/restore workflow which may lead to weakness through a lack of validation of the config state after restore.

Code Example:

Bad

void save_config_state() {

The following pseudo-code is the proper workflow for the integrity checking mitigation:

Code Example:

Good

void save_config_state() {

It must be noted that in the previous example of good pseudo code, the memory (where the hash of the config state is stored) must be trustworthy while the hardware is between the power save and restore states.