5.9. 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
mbedtls
cryptographic 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.The
drivers/auth/mbedtls/mbedtls_*.mk
files contain the list of mbed TLS source files the modules depend upon.include/drivers/auth/mbedtls/mbedtls_config.h
contains 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
make
to build TF-A:MBEDTLS_DIR=<path of the directory containing mbed TLS sources>
TRUSTED_BOARD_BOOT=1
GENERATE_COT=1
By default, this will use the Chain of Trust described in the TBBR-client document. To select a different one, use the
COT
build option.If using a custom build of OpenSSL, set the
OPENSSL_DIR
variable accordingly so it points at the OpenSSL installation path, as explained in Build Options. In addition, set theLD_LIBRARY_PATH
variable when running to point at the custom OpenSSL path, so the OpenSSL libraries are loaded from that path instead of the default OS path. Export this variable if necessary.In the case of Arm platforms, the location of the ROTPK must also be specified at build time. The following locations are currently supported (see
ARM_ROTPK_LOCATION
build option):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 optionbp.trusted_key_storage.public_key
when 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 inplat/arm/board/common/rotpk/arm_rotpk_rsa_sha256.bin
. Enforce generation of the new hash ifROT_KEY
is specified.ARM_ROTPK_LOCATION=devel_ecdsa
: use the default hash located inplat/arm/board/common/rotpk/arm_rotpk_ecdsa_sha256.bin
. Enforce generation of the new hash ifROT_KEY
is specified.ARM_ROTPK_LOCATION=devel_full_dev_rsa_key
: use the key located inplat/arm/board/common/rotpk/arm_full_dev_rsa_rotpk.S
.
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> OPENSSL_DIR=<path-to>/<openssl> \ 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
andfwu_fip
targets 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> OPENSSL_DIR=<path-to>/<openssl> \ 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
Note
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.Note
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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