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diff --git a/docs/design_documents/drtm_poc.rst b/docs/design_documents/drtm_poc.rst new file mode 100644 index 0000000..79e1142 --- /dev/null +++ b/docs/design_documents/drtm_poc.rst @@ -0,0 +1,132 @@ +DRTM Proof of Concept +===================== + +Dynamic Root of Trust for Measurement (DRTM) begins a new trust environment +by measuring and executing a protected payload. + +Static Root of Trust for Measurement (SRTM)/Measured Boot implementation, +currently used by TF-A covers all firmwares, from the boot ROM to the normal +world bootloader. As a whole, they make up the system's TCB. These boot +measurements allow attesting to what software is running on the system and +enable enforcing security policies. + +As the boot chain grows or firmware becomes dynamically extensible, +establishing an attestable TCB becomes more challenging. DRTM provides a +solution to this problem by allowing measurement chains to be started at +any time. As these measurements are stored separately from the boot-time +measurements, they reduce the size of the TCB, which helps reduce the attack +surface and the risk of untrusted code executing, which could compromise +the security of the system. + +Components +~~~~~~~~~~ + + - **DCE-Preamble**: The DCE Preamble prepares the platform for DRTM by + doing any needed configuration, loading the target payload image(DLME), + and preparing input parameters needed by DRTM. Finally, it invokes the + DL Event to start the dynamic launch. + + - **D-CRTM**: The D-CRTM is the trust anchor (or root of trust) for the + DRTM boot sequence and is where the dynamic launch starts. The D-CRTM + must be implemented as a trusted agent in the system. The D-CRTM + initializes the TPM for DRTM and prepares the environment for the next + stage of DRTM, the DCE. The D-CRTM measures the DCE, verifies its + signature, and transfers control to it. + + - **DCE**: The DCE executes on an application core. The DCE verifies the + system’s state, measures security-critical attributes of the system, + prepares the memory region for the target payload, measures the payload, + and finally transfers control to the payload. + + - **DLME**: The protected payload is referred to as the Dynamically Launched + Measured Environment, or DLME. The DLME begins execution in a safe state, + with a single thread of execution, DMA protections, and interrupts + disabled. The DCE provides data to the DLME that it can use to verify the + configuration of the system. + +In this proof of concept, DCE and D-CRTM are implemented in BL31 and +DCE-Preamble and DLME are implemented in UEFI application. A DL Event is +triggered as a SMC by DCE-Preamble and handled by D-CRTM, which launches the +DLME via DCE. + +This manual provides instructions to build TF-A code with pre-buit EDK2 +and DRTM UEFI application. + +Building the PoC for the Arm FVP platform +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +(1) Use the below command to clone TF-A source code - + +.. code:: shell + + $ git clone https://git.trustedfirmware.org/TF-A/trusted-firmware-a.git + +(2) There are prebuilt binaries required to execute the DRTM implementation + in the `prebuilts-drtm-bins`_. + Download EDK2 *FVP_AARCH64_EFI.fd* and UEFI DRTM application *test-disk.img* + binary from `prebuilts-drtm-bins`_. + +(3) Build the TF-A code using below command + +.. code:: shell + + $ make CROSS_COMPILE=aarch64-none-elf- ARM_ROTPK_LOCATION=devel_rsa + DEBUG=1 V=1 BL33=</path/to/FVP_AARCH64_EFI.fd> DRTM_SUPPORT=1 + MBEDTLS_DIR=</path/to/mbedTLS-source> USE_ROMLIB=1 all fip + +Running DRTM UEFI application on the Armv8-A AEM FVP +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +To run the DRTM test application along with DRTM implementation in BL31, +you need an FVP model. Please use the version of FVP_Base_RevC-2xAEMvA model +advertised in the TF-A documentation. + +.. code:: shell + + FVP_Base_RevC-2xAEMvA \ + --data cluster0.cpu0=</path/to/romlib.bin>@0x03ff2000 \ + --stat \ + -C bp.flashloader0.fname=<path/to/fip.bin> \ + -C bp.secureflashloader.fname=<path/to/bl1.bin> \ + -C bp.ve_sysregs.exit_on_shutdown=1 \ + -C bp.virtioblockdevice.image_path=<path/to/test-disk.img> \ + -C cache_state_modelled=1 \ + -C cluster0.check_memory_attributes=0 \ + -C cluster0.cpu0.etm-present=0 \ + -C cluster0.cpu1.etm-present=0 \ + -C cluster0.cpu2.etm-present=0 \ + -C cluster0.cpu3.etm-present=0 \ + -C cluster0.stage12_tlb_size=1024 \ + -C cluster1.check_memory_attributes=0 \ + -C cluster1.cpu0.etm-present=0 \ + -C cluster1.cpu1.etm-present=0 \ + -C cluster1.cpu2.etm-present=0 \ + -C cluster1.cpu3.etm-present=0 \ + -C cluster1.stage12_tlb_size=1024 \ + -C pctl.startup=0.0.0.0 \ + -Q 1000 \ + "$@" + +The bottom of the output from *uart1* should look something like the +following to indicate that the last SMC to unprotect memory has been fired +successfully. + +.. code-block:: shell + + ... + + INFO: DRTM service handler: version + INFO: ++ DRTM service handler: TPM features + INFO: ++ DRTM service handler: Min. mem. requirement features + INFO: ++ DRTM service handler: DMA protection features + INFO: ++ DRTM service handler: Boot PE ID features + INFO: ++ DRTM service handler: TCB-hashes features + INFO: DRTM service handler: dynamic launch + WARNING: DRTM service handler: close locality is not supported + INFO: DRTM service handler: unprotect mem + +-------------- + +*Copyright (c) 2022, Arm Limited. All rights reserved.* + +.. _prebuilts-drtm-bins: https://downloads.trustedfirmware.org/tf-a/drtm +.. _DRTM-specification: https://developer.arm.com/documentation/den0113/a |