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0187c985 SB |
1 | High Assurance Boot (HAB) for i.MX6 CPUs |
2 | ||
8148b824 UC |
3 | To enable the authenticated or encrypted boot mode of U-Boot, it is |
4 | required to set the proper configuration for the target board. This | |
7a037cc9 | 5 | is done by adding the following configuration in the defconfig file: |
8148b824 | 6 | |
7a037cc9 | 7 | CONFIG_SECURE_BOOT=y |
8148b824 UC |
8 | |
9 | In addition, the U-Boot image to be programmed into the | |
0187c985 SB |
10 | boot media needs to be properly constructed, i.e. it must contain a |
11 | proper Command Sequence File (CSF). | |
12 | ||
13 | The Initial Vector Table contains a pointer to the CSF. Please see | |
14 | doc/README.imximage for how to prepare u-boot.imx. | |
15 | ||
16 | The CSF itself is being generated by Freescale HAB tools. | |
17 | ||
18 | mkimage will output additional information about "HAB Blocks" | |
19 | which can be used in the Freescale tooling to authenticate U-Boot | |
20 | (entries in the CSF file). | |
21 | ||
22 | Image Type: Freescale IMX Boot Image | |
23 | Image Ver: 2 (i.MX53/6 compatible) | |
24 | Data Size: 327680 Bytes = 320.00 kB = 0.31 MB | |
25 | Load Address: 177ff420 | |
26 | Entry Point: 17800000 | |
27 | HAB Blocks: 177ff400 00000000 0004dc00 | |
93e14596 | 28 | ^^^^^^^^ ^^^^^^^^ ^^^^^^^^ |
0187c985 SB |
29 | | | | |
30 | | | -------- (1) | |
31 | | | | |
32 | | ------------------- (2) | |
33 | | | |
34 | --------------------------- (3) | |
35 | ||
36 | (1) Size of area in file u-boot.imx to sign | |
37 | This area should include the IVT, the Boot Data the DCD | |
38 | and U-Boot itself. | |
39 | (2) Start of area in u-boot.imx to sign | |
40 | (3) Start of area in RAM to authenticate | |
41 | ||
42 | CONFIG_SECURE_BOOT currently enables only an additional command | |
43 | 'hab_status' in U-Boot to retrieve the HAB status and events. This | |
44 | can be useful while developing and testing HAB. | |
45 | ||
46 | Commands to generate a signed U-Boot using Freescale HAB tools: | |
47 | cst --o U-Boot_CSF.bin < U-Boot.CSF | |
48 | objcopy -I binary -O binary --pad-to 0x2000 --gap-fill=0x00 \ | |
49 | U-Boot_CSF.bin U-Boot_CSF_pad.bin | |
50 | cat u-boot.imx U-Boot_CSF_pad.bin > u-boot-signed.imx | |
51 | ||
52 | NOTE: U-Boot_CSF.bin needs to be padded to the value specified in | |
53 | the imximage.cfg file. | |
0200020b RC |
54 | |
55 | Setup U-Boot Image for Encrypted Boot | |
56 | ------------------------------------- | |
57 | An authenticated U-Boot image is used as starting point for | |
58 | Encrypted Boot. The image is encrypted by Freescale's Code | |
59 | Signing Tool (CST). The CST replaces only the image data of | |
60 | u-boot.imx with the encrypted data. The Initial Vector Table, | |
61 | DCD, and Boot data, remains in plaintext. | |
62 | ||
63 | The image data is encrypted with a Encryption Key (DEK). | |
64 | Therefore, this key is needed to decrypt the data during the | |
65 | booting process. The DEK is protected by wrapping it in a Blob, | |
66 | which needs to be appended to the U-Boot image and specified in | |
67 | the CSF file. | |
68 | ||
69 | The DEK blob is generated by an authenticated U-Boot image with | |
70 | the dek_blob cmd enabled. The image used for DEK blob generation | |
71 | needs to have the following configurations enabled: | |
72 | ||
73 | CONFIG_SECURE_BOOT | |
74 | CONFIG_SYS_FSL_SEC_COMPAT 4 /* HAB version */ | |
75 | CONFIG_FSL_CAAM | |
76 | CONFIG_CMD_DEKBLOB | |
8148b824 | 77 | CONFIG_SYS_FSL_SEC_LE |
0200020b RC |
78 | |
79 | Note: The encrypted boot feature is only supported by HABv4 or | |
80 | greater. | |
81 | ||
82 | The dek_blob command then can be used to generate the DEK blob of | |
83 | a DEK previously loaded in memory. The command is used as follows: | |
84 | ||
85 | dek_blob <DEK address> <Output Address> <Key Size in Bits> | |
86 | example: dek_blob 0x10800000 0x10801000 192 | |
87 | ||
88 | The resulting DEK blob then is used to construct the encrypted | |
89 | U-Boot image. Note that the blob needs to be transferred back | |
90 | to the host.Then the following commands are used to construct | |
91 | the final image. | |
92 | ||
93 | objcopy -I binary -O binary --pad-to 0x2000 --gap-fill=0x00 \ | |
94 | U-Boot_CSF.bin U-Boot_CSF_pad.bin | |
95 | cat u-boot.imx U-Boot_CSF_pad.bin > u-boot-signed.imx | |
96 | objcopy -I binary -O binary --pad-to <blob_dst> --gap-fill=0x00 \ | |
97 | u-boot-signed.imx u-boot-signed-pad.bin | |
98 | cat u-boot-signed-pad.imx DEK_blob.bin > u-boot-encrypted.imx | |
99 | ||
100 | NOTE: u-boot-signed.bin needs to be padded to the value | |
101 | equivalent to the address in which the DEK blob is specified | |
102 | in the CSF. |