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