44 lines
1.7 KiB
Plaintext
44 lines
1.7 KiB
Plaintext
1. Setup U-Boot Image for Encrypted Boot
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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_IMX_HAB=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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