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+ +=======================================================+
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+ + i.MX6, i.MX7 U-Boot Secure Boot guide using HABv4 +
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+ +=======================================================+
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+
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+1. HABv4 secure boot process
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+-----------------------------
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+
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+This document describes a step-by-step procedure on how to sign and securely
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+boot an U-Boot image for non-SPL targets. It is assumed that the reader is
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+familiar with basic HAB concepts and with the PKI tree generation.
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+
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+Details about HAB can be found in the application note AN4581[1] and in the
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+introduction_habv4.txt document.
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+
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+1.1 Building a u-boot-dtb.imx image supporting secure boot
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+-----------------------------------------------------------
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+
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+The U-Boot provides support to secure boot configuration and also provide
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+access to the HAB APIs exposed by the ROM vector table, the support is
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+enabled by selecting the CONFIG_SECURE_BOOT option.
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+
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+When built with this configuration, the U-Boot provides extra functions for
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+HAB, such as the HAB status logs retrievement through the hab_status command
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+and support for extending the root of trust.
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+
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+The U-Boot also correctly pads the final image by aligning to the next 0xC00
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+address, so the CSF signature data generated by CST can be concatenated to
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+image.
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+
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+The diagram below illustrate a signed u-boot-dtb.imx image layout:
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+
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+ ------- +-----------------------------+ <-- *start
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+ ^ | Image Vector Table |
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+ | +-----------------------------+ <-- *boot_data
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+ | | Boot Data |
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+ | +-----------------------------+ <-- *dcd
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+ | | DCD Table |
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+ | +-----------------------------+
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+ Signed | | Padding |
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+ Data | +-----------------------------+ <-- *entry
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+ | | |
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+ | | |
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+ | | u-boot-dtb.bin |
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+ | | |
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+ | | |
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+ | +-----------------------------+
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+ v | Padding |
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+ ------- +-----------------------------+ <-- *csf
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+ | |
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+ | Command Sequence File (CSF) |
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+ | |
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+ +-----------------------------+
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+ | Padding (optional) |
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+ +-----------------------------+
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+
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+1.2 Enabling the secure boot support
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+-------------------------------------
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+
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+The first step is to generate an U-Boot image supporting the HAB features
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+mentioned above, this can be achieved by adding CONFIG_SECURE_BOOT to the
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+build configuration:
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+
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+- Defconfig:
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+
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+ CONFIG_SECURE_BOOT=y
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+
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+- Kconfig:
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+
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+ ARM architecture -> Support i.MX HAB features
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+
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+1.3 Creating the CSF description file
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+--------------------------------------
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+
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+The CSF contains all the commands that the HAB executes during the secure
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+boot. These commands instruct the HAB on which memory areas of the image
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+to authenticate, which keys to install, use and etc.
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+
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+CSF examples are available under doc/imx/habv4/csf_examples/ directory.
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+
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+A build log containing the "Authenticate Data" parameters is available after
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+the U-Boot build, the example below is a log for mx7dsabresd_defconfig target:
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+
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+- mkimage build log:
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+
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+ $ cat u-boot-dtb.imx.log
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+
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+ Image Type: Freescale IMX Boot Image
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+ Image Ver: 2 (i.MX53/6/7 compatible)
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+ Mode: DCD
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+ Data Size: 667648 Bytes = 652.00 KiB = 0.64 MiB
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+ Load Address: 877ff420
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+ Entry Point: 87800000
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+ HAB Blocks: 0x877ff400 0x00000000 0x0009ec00
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+ ^^^^^^^^^^ ^^^^^^^^^^ ^^^^^^^^^^
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+ | | |
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+ | | ------- (1)
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+ | |
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+ | ------------------ (2)
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+ |
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+ ----------------------------- (3)
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+
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+ (1) Size of area in file u-boot-dtb.imx to sign.
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+ This area should include the IVT, the Boot Data the DCD
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+ and the U-Boot itself.
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+ (2) Start of area in u-boot-dtb.imx to sign.
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+ (3) Start of area in RAM to authenticate.
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+
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+- In "Authenticate Data" CSF command users can copy and past the output
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+ addresses:
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+
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+ Block = 0x877ff400 0x00000000 0x0009ec00 "u-boot-dtb.imx"
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+
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+1.4 Signing the U-Boot binary
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+------------------------------
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+
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+The CST tool is used for singing the U-Boot binary and generating a CSF binary,
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+users should input the CSF description file created in the step above and
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+should receive a CSF binary, which contains the CSF commands, SRK table,
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+signatures and certificates.
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+
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+- Create CSF binary file:
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+
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+ $ ./cst -i csf_uboot.txt -o csf_uboot.bin
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+
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+- Append CSF signature to the end of U-Boot image:
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+
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+ $ cat u-boot-dtb.imx csf_uboot.bin > u-boot-signed.imx
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+
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+The u-boot-signed.imx is the signed binary and should be flashed into the boot
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+media.
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+
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+- Flash signed U-Boot binary:
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+
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+ $ sudo dd if=u-boot-signed.imx of=/dev/sd<x> bs=1K seek=1 && sync
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+
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+1.5 Programming SRK Hash
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+-------------------------
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+
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+As explained in AN4581[1] and in introduction_habv4.txt document the SRK Hash
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+fuse values are generated by the srktool and should be programmed in the
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+SoC SRK_HASH[255:0] fuses.
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+
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+Be careful when programming these values, as this data is the basis for the
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+root of trust. An error in SRK Hash results in a part that does not boot.
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+
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+The U-Boot fuse tool can be used for programming eFuses on i.MX SoCs.
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+
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+- Dump SRK Hash fuses values in host machine:
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+
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+ $ hexdump -e '/4 "0x"' -e '/4 "%X""\n"' SRK_1_2_3_4_fuse.bin
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+ 0x20593752
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+ 0x6ACE6962
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+ 0x26E0D06C
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+ 0xFC600661
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+ 0x1240E88F
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+ 0x1209F144
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+ 0x831C8117
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+ 0x1190FD4D
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+
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+- Program SRK_HASH[255:0] fuses, using i.MX6 series as example:
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+
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+ => fuse prog 3 0 0x20593752
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+ => fuse prog 3 1 0x6ACE6962
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+ => fuse prog 3 2 0x26E0D06C
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+ => fuse prog 3 3 0xFC600661
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+ => fuse prog 3 4 0x1240E88F
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+ => fuse prog 3 5 0x1209F144
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+ => fuse prog 3 6 0x831C8117
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+ => fuse prog 3 7 0x1190FD4D
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+
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+The table below lists the SRK_HASH bank and word according to the i.MX device:
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+
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+ +-------------------+---------------+---------------+---------------+
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+ | | i.MX6 Series | i.MX7D/S | i.MX7ULP |
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+ +-------------------+---------------+---------------+---------------+
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+ | SRK_HASH[31:00] | bank 3 word 0 | bank 6 word 0 | bank 5 word 0 |
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+ +-------------------+---------------+---------------+---------------+
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+ | SRK_HASH[63:32] | bank 3 word 1 | bank 6 word 1 | bank 5 word 1 |
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+ +-------------------+---------------+---------------+---------------+
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+ | SRK_HASH[95:64] | bank 3 word 2 | bank 6 word 2 | bank 5 word 2 |
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+ +-------------------+---------------+---------------+---------------+
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+ | SRK_HASH[127:96] | bank 3 word 3 | bank 6 word 3 | bank 5 word 3 |
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+ +-------------------+---------------+---------------+---------------+
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+ | SRK_HASH[159:128] | bank 3 word 4 | bank 7 word 0 | bank 5 word 4 |
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+ +-------------------+---------------+---------------+---------------+
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+ | SRK_HASH[191:160] | bank 3 word 5 | bank 7 word 1 | bank 5 word 5 |
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+ +-------------------+---------------+---------------+---------------+
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+ | SRK_HASH[223:192] | bank 3 word 6 | bank 7 word 2 | bank 5 word 6 |
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+ +-------------------+---------------+---------------+---------------+
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+ | SRK_HASH[255:224] | bank 3 word 7 | bank 7 word 3 | bank 5 word 7 |
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+ +-------------------+---------------+---------------+---------------+
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+
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+1.6 Verifying HAB events
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+-------------------------
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+
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+The next step is to verify that the signature attached to U-Boot is
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+successfully processed without errors. HAB generates events when processing
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+the commands if it encounters issues.
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+
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+The hab_status U-Boot command call the hab_report_event() and hab_status()
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+HAB API functions to verify the processor security configuration and status.
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+This command displays any events that were generated during the process.
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+
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+Prior to closing the device users should ensure no HAB events were found, as
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+the example below:
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+
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+- Verify HAB events:
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+
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+ => hab_status
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+
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+ Secure boot disabled
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+
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+ HAB Configuration: 0xf0, HAB State: 0x66
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+ No HAB Events Found!
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+
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+1.7 Closing the device
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+-----------------------
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+
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+After the device successfully boots a signed image without generating any HAB
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+events, it is safe to close the device. This is the last step in the HAB
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+process, and is achieved by programming the SEC_CONFIG[1] fuse bit.
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+
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+Once the fuse is programmed, the chip does not load an image that has not been
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+signed using the correct PKI tree.
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+
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+- Program SEC_CONFIG[1] fuse, using i.MX6 series as example:
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+
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+ => fuse prog 0 6 0x00000002
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+
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+The table below list the SEC_CONFIG[1] bank and word according to the i.MX
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+device:
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+
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+ +--------------+-----------------+------------+
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+ | Device | Bank and Word | Value |
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+ +--------------+-----------------+------------+
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+ | i.MX6 Series | bank 0 word 6 | 0x00000002 |
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+ +--------------+-----------------+------------+
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+ | i.MX7D/S | bank 1 word 3 | 0x02000000 |
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+ +--------------+-----------------+------------+
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+ | i.MX7ULP | bank 29 word 6 | 0x80000000 |
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+ +--------------+-----------------+------------+
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+
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+1.8 Completely secure the device
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+---------------------------------
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+
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+Additional fuses can be programmed for completely secure the device, more
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+details about these fuses and their possible impact can be found at AN4581[1].
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+
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+- Program SRK_LOCK, using i.MX6 series as example:
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+
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+ => fuse prog 0 0 0x4000
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+
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+- Program DIR_BT_DIS, using i.MX6 series as example:
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+
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+ => fuse prog 0 6 0x8
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+
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+- Program SJC_DISABLE, using i.MX6 series as example:
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+
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+ => fuse prog 0 6 0x100000
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+
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+- JTAG_SMODE, using i.MX6 series as example:
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+
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+ => fuse prog 0 6 0xC00000
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+
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+The table below list the SRK_LOCK, DIR_BT_DIS, SJC_DISABLE, and JTAG_SMODE bank
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+and word according to the i.MX device:
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+
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+ +--------------+---------------+------------+
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+ | Device | Bank and Word | Value |
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+ +--------------+---------------+------------+
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+ | SRK_LOCK |
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+ +-------------------------------------------+
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+ | i.MX6 Series | bank 0 word 0 | 0x00004000 |
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+ +--------------+---------------+------------+
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+ | i.MX7D/S | bank 0 word 0 | 0x00000200 |
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+ +--------------+---------------+------------+
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+ | i.MX7ULP | bank 1 word 1 | 0x00000080 |
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+ +--------------+---------------+------------+
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+ | DIR_BT_DIS |
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+ +-------------------------------------------+
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+ | i.MX6 Series | bank 0 word 6 | 0x00000008 |
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+ +--------------+---------------+------------+
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+ | i.MX7D/S | bank 1 word 3 | 0x08000000 |
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+ +--------------+---------------+------------+
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+ | i.MX7ULP | bank 1 word 1 | 0x00002000 |
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+ +--------------+---------------+------------+
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+ | SJC_DISABLE |
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+ +-------------------------------------------+
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+ | i.MX6 Series | bank 0 word 6 | 0x00100000 |
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+ +--------------+---------------+------------+
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+ | i.MX7D/S | bank 1 word 3 | 0x00200000 |
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+ +--------------+---------------+------------+
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+ | i.MX7ULP | bank 1 word 1 | 0x00000020 |
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+ +--------------+---------------+------------+
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+ | JTAG_SMODE |
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+ +-------------------------------------------+
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+ | i.MX6 Series | bank 0 word 6 | 0x00C00000 |
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+ +--------------+---------------+------------+
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+ | i.MX7D/S | bank 1 word 3 | 0x00C00000 |
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+ +--------------+---------------+------------+
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+ | i.MX7ULP | bank 1 word 1 | 0x000000C0 |
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+ +--------------+---------------+------------+
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+
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+2. Extending the root of trust
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+-------------------------------
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+
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+The High Assurance Boot (HAB) code located in the on-chip ROM provides an
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+Application Programming Interface (API) making it possible to call back
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+into the HAB code for authenticating additional boot images.
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+
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+The U-Boot supports this feature and can be used to authenticate the Linux
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+Kernel Image.
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+
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+The process of signing an additional image is similar to the U-Boot.
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+The diagram below illustrate the zImage layout:
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+
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+ ------- +-----------------------------+ <-- *load_address
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+ ^ | |
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+ | | |
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+ | | |
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+ | | |
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+ | | zImage |
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+ Signed | | |
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+ Data | | |
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+ | | |
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+ | +-----------------------------+
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+ | | Padding Next Boundary |
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+ | +-----------------------------+ <-- *ivt
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+ v | Image Vector Table |
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+ ------- +-----------------------------+ <-- *csf
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+ | |
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+ | Command Sequence File (CSF) |
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+ | |
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+ +-----------------------------+
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+ | Padding (optional) |
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+ +-----------------------------+
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+
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+2.1 Padding the image
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+----------------------
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+
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+The zImage must be padded to the next boundary address (0x1000), for instance
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+if the image size is 0x649920 it must be padded to 0x64A000.
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+
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+The tool objcopy can be used for padding the image.
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+
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+- Pad the zImage:
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+
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+ $ objcopy -I binary -O binary --pad-to 0x64A000 --gap-fill=0x00 \
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+ zImage zImage_pad.bin
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+
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+2.2 Generating Image Vector Table
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+----------------------------------
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+
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+The HAB code requires an Image Vector Table (IVT) for determining the image
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+length and the CSF location. Since zImage does not include an IVT this has
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+to be manually created and appended to the end of the padded zImage, the
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+script genIVT.pl in script_examples directory can be used as reference.
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+
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+- Generate IVT:
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+
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+ $ genIVT.pl
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+
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+Note: The load Address may change depending on the device.
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+
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+- Append the ivt.bin at the end of the padded zImage:
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+
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+ $ cat zImage_pad.bin ivt.bin > zImage_pad_ivt.bin
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+
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+2.3 Signing the image
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+----------------------
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+
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+A CSF file has to be created to sign the image. HAB does not allow to change
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+the SRK once the first image is authenticated, so the same SRK key used in
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+U-Boot must be used when extending the root of trust.
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+
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+CSF examples are available in ../csf_examples/additional_images/
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+directory.
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+
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+- Create CSF binary file:
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+
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+ $ ./cst --i csf_additional_images.txt --o csf_zImage.bin
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+
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+- Attach the CSF binary to the end of the image:
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+
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+ $ cat zImage_pad_ivt.bin csf_zImage.bin > zImage_signed.bin
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+
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+2.4 Verifying HAB events
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+-------------------------
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+
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+The U-Boot includes the hab_auth_img command which can be used for
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+authenticating and troubleshooting the signed image, zImage must be
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+loaded at the load address specified in the IVT.
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+
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+- Authenticate additional image:
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+
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+ => hab_auth_img <Load Address> <Image Size> <IVT Offset>
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+
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+If no HAB events were found the zImage is successfully signed.
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+
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+References:
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+[1] AN4581: "Secure Boot on i.MX 50, i.MX 53, i.MX 6 and i.MX 7 Series using
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+ HABv4" - Rev 2.
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