The following section describes the components used in the silicon test environment.
- opentitantool: provides a common interface to interact with an OpenTitan Device Under Test (DUT). Leverages opentitanlib to expose DUT common functionality such as SPI bootstrap, reset, and general DUT I/O interfaces. Written in Rust.
- opentitanlib (documentation): implements interfaces to access DUT functionality through various backend interfaces. Backed interfaces are used to abstract various target configurations (e.g. FPGA vs Verilator vs Silicon). Written in Rust.
- test software: implement DUT test sequences. The most basic test program loads a binary into the DUT using the spi bootstrap protocol and polls the UART interface for results. All test cases are written in Rust.
- Bazel: OpenTitan software build system. Used to build host and device (DUT) software and trigger unit tests as well as tests requiring an OpenTitan target. FPGA, Verilator and Silicon targets are supported. DV test targets are integrated using dvsim.
- hsmtool: utility used to interface with hardware used to manage signing keys. The tool uses PKCS#11 to access HSM and USB tokens. Only NitroKey HSM2 is supported at the moment.
- hyperdebug: standard OpenTitan test board interface. Implements a DUT hardware abstraction layer (hyperdebug firmware) used to drive DUT peripheral interfaces. opentitantool supports a hyperdebug backend implementation.
- test board: Additional test boards are going to be used to support silicon validation, pentesting and integration activities. It is strongly recommended that all test boards support hyperdebug to simplify DUT management. Boards without hyperdebug support will require a custom backend in opentitantool.
- OTP: One-Time-Programmable memory. Defines the DUT lifecycle and various hardware and software configuration settings.
- ROM: Read-Only Memory (ROM) boot firmware. As its name suggests, this component is non-mutable and fixed at tape-out time. The code is not signed but is physically and logically protected by the DUT hardware, hence it is used as the Root of Trust in the DUT secure boot implementation.
- ROM_EXT: ROM extensions stored in mutable memory. Depending on the lifecycle of the device and mode of execution, this boot component may be required to support signature verification and execution of DUT test programs.
- OpenTitan Test Framework (OTTF): On-Device Test Framework used to instrument test programs.
- HSM/Signing Fob: Hardware backed storage for signing keys.
- JTAG: JTAG interface to OpenTitan rv_dm and lc_ctrl TAP interfaces.
- Common Criteria certified test lab; or,
- Test lab meeting MSSR guidelines and that is in the process of being certified as a site or as part of the certification of an OpenTitan device
- Any testing performed outside a secure environment.
There are various modes of firmware execution aiming to provide flexible DUT and code signing configurations. The following sections describe the available modes of execution for Silicon Validation.
Covers any of the following:
- DUT test binaries signed with ROM keys. Binary is loaded into DUT via bootstrap. The ROM verifies the binary signature before starting execution. Code signing requires access to TEST or DEV signing keys, which can be loaded into USB signing fobs.
- DUT binaries loaded into SRAM or flash via JTAG in TEST_UNLOCKED, DEV or RMA stages. In this case binaries don’t necessarily need to be signed depending on how the device is configured via JTAG.
Bare metal execution provides a high level of configurability, potentially leaving the DUTs exposed to potential vulnerability identification. For this reason, this mode of execution is restricted to secure environments.
ROM_EXT developers without access to secure environments will be required to perform most of the development using an FPGA target.
Represents custom ROM_EXT binaries supporting a special configuration not available in a production signed ROM_EXT binary. The ROM_EXT is signed with a usage constraints manifest allowing it to run only on a DUT with a matching device identifier. This is done to mitigate the exposure of any potential vulnerabilities released in the custom configuration.
Another potential use case is to implement sample management policies backed by the signing configuration. For example, if there is a requirement to distribute individual signing fobs per DUT.
The ROM_EXT itself may opt to only support node-locked binary payloads. This is useful in cases in which it is required to enforce node-locked policies for later boot stages.
Represents ROM_EXT binaries signed with production keys. These binaries are expected to be of production quality from a functional and security perspective. DUTs distributed with production ROM_EXT will be required to support test programs signed with keys known to the ROM_EXT. This can be supported via ownership transfer and/or by a ROM_EXT with embedded verification keys.
- For test chips, it is expected that some vulnerabilities will be detected during the penetration test phase. It is then important to discontinue PROD signing keys used to sign ROM_EXT binaries with exposed critical vulnerabilities.
- Due to the previous point, it is also important to rotate all ROM keys between tape-outs.
|Lifecycle||Bare Metal||Node Locked||PROD ROM_EXT|
|Lifecycle||Bare Metal||Node Locked||PROD ROM_EXT|