6d7403bf72
The README.mxc_hab is outdated and need improvements, add the following modifications: - Reorganize document and remove duplicate content - Add CST download link - Update CST package name - Align command lines with CST v2.3.3 - Update U-Boot binary name - Remove CSF padding since is not documented in AN4581 Signed-off-by: Breno Lima <breno.lima@nxp.com>
145 lines
5.4 KiB
Plaintext
145 lines
5.4 KiB
Plaintext
1. High Assurance Boot (HAB) for i.MX CPUs
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------------------------------------------
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To enable the authenticated or encrypted boot mode of U-Boot, it is
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required to set the proper configuration for the target board. This
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is done by adding the following configuration in the defconfig file:
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CONFIG_SECURE_BOOT=y
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In addition, 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 CSF itself is generated by the i.MX High Assurance Boot Reference
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Code Signing Tool.
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https://www.nxp.com/webapp/sps/download/license.jsp?colCode=IMX_CST_TOOL
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More information about the CSF and HAB can be found in the AN4581.
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https://www.nxp.com/docs/en/application-note/AN4581.pdf
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We don't want to explain how to create a PKI tree or SRK table as
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this is well explained in the Application Note.
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2. Secure Boot on non-SPL targets
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---------------------------------
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On non-SPL targets a singe U-Boot binary is generated, mkimage will
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output additional information about "HAB Blocks" which can be used
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in the CST to authenticate the U-Boot image (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-dtb.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-dtb.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 i.MX HAB CST tool:
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# Compile CSF and create signature
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cst --o csf-u-boot.bin --i command_sequence_uboot.csf
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# Append compiled CSF to Binary
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cat u-boot-dtb.imx csf-u-boot.bin > u-boot-signed.imx
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3. Secure Boot on SPL targets
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-----------------------------
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This version of U-Boot is able to build a signable version of the SPL
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as well as a signable version of the U-Boot image. The signature can
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be verified through High Assurance Boot (HAB).
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After building, you need to create a command sequence file and use
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i.MX HAB Code Signing Tool to sign both binaries. After creation,
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the mkimage tool outputs the required information about the HAB Blocks
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parameter for the CSF. During the build, the information is preserved
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in log files named as the binaries. (SPL.log and u-boot-ivt.log).
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Example Output of the SPL (imximage) creation:
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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: 61440 Bytes = 60.00 kB = 0.06 MB
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Load Address: 00907420
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Entry Point: 00908000
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HAB Blocks: 00907400 00000000 0000cc00
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Example Output of the u-boot-ivt.img (firmware_ivt) creation:
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Image Name: U-Boot 2016.11-rc1-31589-g2a4411
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Created: Sat Nov 5 21:53:28 2016
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Image Type: ARM U-Boot Firmware with HABv4 IVT (uncompressed)
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Data Size: 352192 Bytes = 343.94 kB = 0.34 MB
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Load Address: 17800000
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Entry Point: 00000000
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HAB Blocks: 0x177fffc0 0x0000 0x00054020
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# Compile CSF and create signature
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cst --o csf-u-boot.bin --i command_sequence_uboot.csf
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cst --o csf-SPL.bin --i command_sequence_spl.csf
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# Append compiled CSF to Binary
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cat SPL csf-SPL.bin > SPL-signed
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cat u-boot-ivt.img csf-u-boot.bin > u-boot-signed.img
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These two signed binaries can be used on an i.MX in closed
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configuration when the according SRK Table Hash has been flashed.
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4. Setup U-Boot Image for Encrypted Boot
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----------------------------------------
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An authenticated U-Boot image is used as starting point for
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Encrypted Boot. The image is encrypted by i.MX Code Signing
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Tool (CST). The CST replaces only the image data of
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u-boot-dtb.imx with the encrypted data. The Initial Vector Table,
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DCD, and Boot data, remains in plaintext.
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The image data is encrypted with a Encryption Key (DEK).
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Therefore, this key is needed to decrypt the data during the
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booting process. The DEK is protected by wrapping it in a Blob,
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which needs to be appended to the U-Boot image and specified in
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the CSF file.
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The DEK blob is generated by an authenticated U-Boot image with
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the dek_blob cmd enabled. The image used for DEK blob generation
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needs to have the following configurations enabled in Kconfig:
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CONFIG_SECURE_BOOT=y
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CONFIG_CMD_DEKBLOB=y
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Note: The encrypted boot feature is only supported by HABv4 or
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greater.
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The dek_blob command then can be used to generate the DEK blob of
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a DEK previously loaded in memory. The command is used as follows:
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dek_blob <DEK address> <Output Address> <Key Size in Bits>
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example: dek_blob 0x10800000 0x10801000 192
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The resulting DEK blob then is used to construct the encrypted
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U-Boot image. Note that the blob needs to be transferred back
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to the host.Then the following commands are used to construct
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the final image.
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cat u-boot-dtb.imx csf-u-boot.bin > u-boot-signed.imx
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objcopy -I binary -O binary --pad-to <blob_dst> --gap-fill=0x00 \
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u-boot-signed.imx u-boot-signed-pad.bin
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cat u-boot-signed-pad.imx DEK_blob.bin > u-boot-encrypted.imx
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NOTE: u-boot-signed.bin needs to be padded to the value
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equivalent to the address in which the DEK blob is specified
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in the CSF.
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