doc: imx6: add section for secure boot with SPL

Cc: sbabic@denx.de
Signed-off-by: Sven Ebenfeld <sven.ebenfeld@gmail.com>
Reviewed-by: George McCollister <george.mccollister@gmail.com>

diff --git a/doc/README.imx6 b/doc/README.imx6
index 73b8b0b..add1d80 100644 (file)
--- a/doc/README.imx6
+++ b/doc/README.imx6
@@ -138,3 +138,51 @@ c
 The last "c" command tells kermit (from ckermit package in most distros)
 to switch from command line mode to communication mode, and when the
 script is finished, the U-Boot prompt is shown in the same shell.
 The last "c" command tells kermit (from ckermit package in most distros)
 to switch from command line mode to communication mode, and when the
 script is finished, the U-Boot prompt is shown in the same shell.

+
+3. Using Secure Boot on i.MX6 machines with SPL support
+-------------------------------------------------------
+
+This version of U-Boot is able to build a signable version of the SPL
+as well as a signable version of the U-Boot image. The signature can
+be verified through High Assurance Boot (HAB).
+
+CONFIG_SECURE_BOOT is needed to build those two binaries.
+After building, you need to create a command sequence file and use
+Freescales Code Signing Tool to sign both binaries. After creation,
+the mkimage tool outputs the required information about the HAB Blocks
+parameter for the CSF.
+
+More information about the CSF and HAB can be found in the AN4581.
+https://cache.freescale.com/files/32bit/doc/app_note/AN4581.pdf
+
+We don't want to explain how to create a PKI tree or SRK table as
+this is well explained in the Application Note.
+
+Example Output of the SPL (imximage) creation:
+ Image Type:   Freescale IMX Boot Image
+ Image Ver:    2 (i.MX53/6/7 compatible)
+ Mode:         DCD
+ Data Size:    61440 Bytes = 60.00 kB = 0.06 MB
+ Load Address: 00907420
+ Entry Point:  00908000
+ HAB Blocks:   00907400 00000000 0000cc00
+
+Example Output of the u-boot-ivt.img (firmware_ivt) creation:
+ Image Name:   U-Boot 2016.11-rc1-31589-g2a4411
+ Created:      Sat Nov  5 21:53:28 2016
+ Image Type:   ARM U-Boot Firmware with HABv4 IVT (uncompressed)
+ Data Size:    352192 Bytes = 343.94 kB = 0.34 MB
+ Load Address: 17800000
+ Entry Point:  00000000
+ HAB Blocks:   0x177fffc0   0x0000   0x00054020
+
+The CST (Code Signing Tool) can be downloaded from NXP.
+# Compile CSF and create signature
+./cst --o csf-u-boot.bin < command_sequence_uboot.csf
+./cst --o csf-SPL.bin < command_sequence_spl.csf
+# Append compiled CSF to Binary
+cat SPL csf-SPL.bin > SPL-signed
+cat u-boot-ivt.img csf-u-boot.bin > u-boot-signed.img
+
+These two signed binaries can be used on an i.MX6 in closed
+configuration when the according SRK Table Hash has been flashed.
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