9. Building FIP images with support for Trusted Board Boot¶
Trusted Board Boot primarily consists of the following two features:
Image Authentication, described in Trusted Board Boot, and
Firmware Update, described in Firmware Update (FWU)
The following steps should be followed to build FIP and (optionally) FWU_FIP images with support for these features:
Fulfill the dependencies of the
mbedtlscryptographic and image parser modules by checking out a recent version of the mbed TLS Repository. It is important to use a version that is compatible with TF-A and fixes any known security vulnerabilities. See mbed TLS Security Center for more information. See the Prerequisites document for the appropriate version of mbed TLS to use.
drivers/auth/mbedtls/mbedtls_*.mkfiles contain the list of mbed TLS source files the modules depend upon.
include/drivers/auth/mbedtls/mbedtls_config.hcontains the configuration options required to build the mbed TLS sources.
Note that the mbed TLS library is licensed under the Apache version 2.0 license. Using mbed TLS source code will affect the licensing of TF-A binaries that are built using this library.
To build the FIP image, ensure the following command line variables are set while invoking
maketo build TF-A:
MBEDTLS_DIR=<path of the directory containing mbed TLS sources>
By default, this will use the Chain of Trust described in the TBBR-client document. To select a different one, use the
In the case of Arm platforms, the location of the ROTPK hash must also be specified at build time. The following locations are currently supported (see
ARM_ROTPK_LOCATION=regs: the ROTPK hash is obtained from the Trusted root-key storage registers present in the platform. On Juno, these registers are read-only. On FVP Base and Cortex models, the registers are also read-only, but the value can be specified using the command line option
bp.trusted_key_storage.public_keywhen launching the model. On Juno board, the default value corresponds to an ECDSA-SECP256R1 public key hash, whose private part is not currently available.
ARM_ROTPK_LOCATION=devel_rsa: use the default hash located in
plat/arm/board/common/rotpk/arm_rotpk_rsa_sha256.bin. Enforce generation of the new hash if
ARM_ROTPK_LOCATION=devel_ecdsa: use the default hash located in
plat/arm/board/common/rotpk/arm_rotpk_ecdsa_sha256.bin. Enforce generation of the new hash if
Example of command line using RSA development keys:
MBEDTLS_DIR=<path of the directory containing mbed TLS sources> \ make PLAT=<platform> TRUSTED_BOARD_BOOT=1 GENERATE_COT=1 \ ARM_ROTPK_LOCATION=devel_rsa \ ROT_KEY=plat/arm/board/common/rotpk/arm_rotprivk_rsa.pem \ BL33=<path-to>/<bl33_image> \ all fip
The result of this build will be the bl1.bin and the fip.bin binaries. This FIP will include the certificates corresponding to the selected Chain of Trust. These certificates can also be found in the output build directory.
The optional FWU_FIP contains any additional images to be loaded from Non-Volatile storage during the Firmware Update (FWU) process. To build the FWU_FIP, any FWU images required by the platform must be specified on the command line. On Arm development platforms like Juno, these are:
NS_BL2U. The AP non-secure Firmware Updater image.
SCP_BL2U. The SCP Firmware Update Configuration image.
Example of Juno command line for generating both
fwu_fiptargets using RSA development:
MBEDTLS_DIR=<path of the directory containing mbed TLS sources> \ make PLAT=juno TRUSTED_BOARD_BOOT=1 GENERATE_COT=1 \ ARM_ROTPK_LOCATION=devel_rsa \ ROT_KEY=plat/arm/board/common/rotpk/arm_rotprivk_rsa.pem \ BL33=<path-to>/<bl33_image> \ SCP_BL2=<path-to>/<scp_bl2_image> \ SCP_BL2U=<path-to>/<scp_bl2u_image> \ NS_BL2U=<path-to>/<ns_bl2u_image> \ all fip fwu_fip
The BL2U image will be built by default and added to the FWU_FIP. The user may override this by adding
BL2U=<path-to>/<bl2u_image>to the command line above.
Building and installing the non-secure and SCP FWU images (NS_BL1U, NS_BL2U and SCP_BL2U) is outside the scope of this document.
The result of this build will be bl1.bin, fip.bin and fwu_fip.bin binaries. Both the FIP and FWU_FIP will include the certificates corresponding to the selected Chain of Trust. These certificates can also be found in the output build directory.
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