Add license and readme files.

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  1. LICENSE
  2. README.md
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  6. secure_storage.cpp
README.md

Access-controlled NVRAM app for Trusty

This repository contains code to host the reference implementation of Android‘s Access-Controlled NVRAM HAL in a Trusty app. The app exposes its service via a standard Trusty IPC endpoint, accepting commands and producing replies in the message format defined by the reference implementation. The app relies on Trusty’s secure storage abstraction to store persistent NVRAM space contents and meta data.

IMPORTANT NOTE: The Access-Controlled NVRAM HAL spec calls for locked NVRAM contents to be persisted “until the next full device reset”. This means that locked persistent NVRAM spaces must remain intact unless the user factory-resets the entire device. In particular, NVRAM data may not be lost unless all other device state gets wiped as well. The code in this repository DOES NOT achieve this in its current state. To achieve compliance with the HAL spec, an implementation can implement one of the following approaches:

  • Use tamper-evident storage and enforce a full device wipe upon detecting tampering with NVRAM data. The code as is uses tamper-evident storage (as provided by STORAGE_CLIENT_TDEA_PORT), but Trusty‘s secure storage layer currently (1) can’t distinguish tampering from initial setup and (2) doesn't indicate to the app when tampering has been detected.
  • Use tamper-resistant storage (e.g. switch to STORAGE_CLIENT_TP_PORT) to enable secure storage to store NVRAM state in RPMB and make sure that NVRAM data gets wiped as part of hardware reset. This will generally require bootloader/recovery integration, which should either use an out-of-band approach to clear RPMB during hardware reset / recovery or send COMMAND_DISABLE_WIPE and COMMAND_WIPE_STORAGE to the Trusty NVRAM app at the appropriate points during boot and recovery, respectively.