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High Assurance Boot (HAB) for i.MX6 CPUs
To authenticate U-Boot only by the CPU there is no code required in
U-Boot itself. However, the U-Boot image to be programmed into the
boot media needs to be properly constructed, i.e. it must contain a
proper Command Sequence File (CSF).
The Initial Vector Table contains a pointer to the CSF. Please see
doc/README.imximage for how to prepare u-boot.imx.
The CSF itself is being generated by Freescale HAB tools.
mkimage will output additional information about "HAB Blocks"
which can be used in the Freescale tooling to authenticate U-Boot
(entries in the CSF file).
Image Type: Freescale IMX Boot Image
Image Ver: 2 (i.MX53/6 compatible)
Data Size: 327680 Bytes = 320.00 kB = 0.31 MB
Load Address: 177ff420
Entry Point: 17800000
HAB Blocks: 177ff400 00000000 0004dc00
^^^^^^^^ ^^^^^^^^ ^^^^^^^^
| | |
| | -------- (1)
| |
| ------------------- (2)
--------------------------- (3)
(1) Size of area in file u-boot.imx to sign
This area should include the IVT, the Boot Data the DCD
and U-Boot itself.
(2) Start of area in u-boot.imx to sign
(3) Start of area in RAM to authenticate
CONFIG_SECURE_BOOT currently enables only an additional command
'hab_status' in U-Boot to retrieve the HAB status and events. This
can be useful while developing and testing HAB.
Commands to generate a signed U-Boot using Freescale HAB tools:
cst --o U-Boot_CSF.bin < U-Boot.CSF
objcopy -I binary -O binary --pad-to 0x2000 --gap-fill=0x00 \
U-Boot_CSF.bin U-Boot_CSF_pad.bin
cat u-boot.imx U-Boot_CSF_pad.bin > u-boot-signed.imx
NOTE: U-Boot_CSF.bin needs to be padded to the value specified in
the imximage.cfg file.