1High Assurance Boot (HAB) for i.MX6 CPUs 2 3To enable the authenticated or encrypted boot mode of U-Boot, it is 4required to set the proper configuration for the target board. This 5is done by adding the following configuration in in the proper config 6file (e.g. include/configs/mx6qarm2.h) 7 8#define CONFIG_SECURE_BOOT 9 10In addition, the U-Boot image to be programmed into the 11boot media needs to be properly constructed, i.e. it must contain a 12proper Command Sequence File (CSF). 13 14The Initial Vector Table contains a pointer to the CSF. Please see 15doc/README.imximage for how to prepare u-boot.imx. 16 17The CSF itself is being generated by Freescale HAB tools. 18 19mkimage will output additional information about "HAB Blocks" 20which can be used in the Freescale tooling to authenticate U-Boot 21(entries in the CSF file). 22 23Image Type: Freescale IMX Boot Image 24Image Ver: 2 (i.MX53/6 compatible) 25Data Size: 327680 Bytes = 320.00 kB = 0.31 MB 26Load Address: 177ff420 27Entry Point: 17800000 28HAB Blocks: 177ff400 00000000 0004dc00 29 ^^^^^^^^ ^^^^^^^^ ^^^^^^^^ 30 | | | 31 | | -------- (1) 32 | | 33 | ------------------- (2) 34 | 35 --------------------------- (3) 36 37(1) Size of area in file u-boot.imx to sign 38 This area should include the IVT, the Boot Data the DCD 39 and U-Boot itself. 40(2) Start of area in u-boot.imx to sign 41(3) Start of area in RAM to authenticate 42 43CONFIG_SECURE_BOOT currently enables only an additional command 44'hab_status' in U-Boot to retrieve the HAB status and events. This 45can be useful while developing and testing HAB. 46 47Commands to generate a signed U-Boot using Freescale HAB tools: 48cst --o U-Boot_CSF.bin < U-Boot.CSF 49objcopy -I binary -O binary --pad-to 0x2000 --gap-fill=0x00 \ 50 U-Boot_CSF.bin U-Boot_CSF_pad.bin 51cat u-boot.imx U-Boot_CSF_pad.bin > u-boot-signed.imx 52 53NOTE: U-Boot_CSF.bin needs to be padded to the value specified in 54the imximage.cfg file. 55 56Setup U-Boot Image for Encrypted Boot 57------------------------------------- 58An authenticated U-Boot image is used as starting point for 59Encrypted Boot. The image is encrypted by Freescale's Code 60Signing Tool (CST). The CST replaces only the image data of 61u-boot.imx with the encrypted data. The Initial Vector Table, 62DCD, and Boot data, remains in plaintext. 63 64The image data is encrypted with a Encryption Key (DEK). 65Therefore, this key is needed to decrypt the data during the 66booting process. The DEK is protected by wrapping it in a Blob, 67which needs to be appended to the U-Boot image and specified in 68the CSF file. 69 70The DEK blob is generated by an authenticated U-Boot image with 71the dek_blob cmd enabled. The image used for DEK blob generation 72needs to have the following configurations enabled: 73 74CONFIG_SECURE_BOOT 75CONFIG_SYS_FSL_SEC_COMPAT 4 /* HAB version */ 76CONFIG_FSL_CAAM 77CONFIG_CMD_DEKBLOB 78CONFIG_SYS_FSL_SEC_LE 79 80Note: The encrypted boot feature is only supported by HABv4 or 81greater. 82 83The dek_blob command then can be used to generate the DEK blob of 84a DEK previously loaded in memory. The command is used as follows: 85 86dek_blob <DEK address> <Output Address> <Key Size in Bits> 87example: dek_blob 0x10800000 0x10801000 192 88 89The resulting DEK blob then is used to construct the encrypted 90U-Boot image. Note that the blob needs to be transferred back 91to the host.Then the following commands are used to construct 92the final image. 93 94objcopy -I binary -O binary --pad-to 0x2000 --gap-fill=0x00 \ 95 U-Boot_CSF.bin U-Boot_CSF_pad.bin 96cat u-boot.imx U-Boot_CSF_pad.bin > u-boot-signed.imx 97objcopy -I binary -O binary --pad-to <blob_dst> --gap-fill=0x00 \ 98 u-boot-signed.imx u-boot-signed-pad.bin 99cat u-boot-signed-pad.imx DEK_blob.bin > u-boot-encrypted.imx 100 101 NOTE: u-boot-signed.bin needs to be padded to the value 102 equivalent to the address in which the DEK blob is specified 103 in the CSF. 104