The current U-Boot implementation includes SPL targets for some NXP development boards:
- mx6sabreauto_defconfig - mx6sabresd_defconfig - mx6ul_14x14_evk_defconfig - mx6ul_9x9_evk_defconfig
Add additional steps needed to completly secure the bootloader image.
Signed-off-by: Breno Lima breno.lima@nxp.com --- .../habv4/guides/mx6_mx7_spl_secure_boot.txt | 181 ++++++++++++++++++ 1 file changed, 181 insertions(+) create mode 100644 doc/imx/habv4/guides/mx6_mx7_spl_secure_boot.txt
diff --git a/doc/imx/habv4/guides/mx6_mx7_spl_secure_boot.txt b/doc/imx/habv4/guides/mx6_mx7_spl_secure_boot.txt new file mode 100644 index 0000000000..0d7931aac0 --- /dev/null +++ b/doc/imx/habv4/guides/mx6_mx7_spl_secure_boot.txt @@ -0,0 +1,181 @@ + +===============================================================+ + + i.MX6, i.MX7 U-Boot HABv4 Secure Boot guide for SPL targets + + +===============================================================+ + +1. HABv4 secure boot process +----------------------------- + +This document is an addendum of mx6_mx7_secure_boot.txt guide describing a +step-by-step procedure on how to sign and securely boot an U-Boot image for +SPL targets. + +Details about HAB can be found in the application note AN4581[1] and in the +introduction_habv4.txt document. + +1.1 Building a SPL target supporting secure boot +------------------------------------------------- + +The U-Boot provides Second Program Loader (SPL) support which generates two +final images, SPL and U-Boot proper. The HABv4 can be used to authenticate +both binaries. + +Out of reset the ROM code authenticates the SPL which is responsible for +initializing essential features such as DDR, UART, PMIC and clock +enablement. Once the DDR is available, the SPL code loads the U-Boot proper +image to its specific execution address and call the HAB APIs to extend the +root of trust. + +The U-Boot provides support to secure boot configuration and also provide +access to the HAB APIs exposed by the ROM vector table, the support is +enabled by selecting the CONFIG_SECURE_BOOT option. + +When built with this configuration the U-Boot correctly pads the final SPL +image by aligning to the next 0xC00 address, so the CSF signature data +generated by CST can be concatenated to the image. + +The U-Boot also append an Image Vector Table (IVT) in the final U-Boot proper +binary (u-boot-ivt.img) so it can be used by HAB API in a post ROM stage. + +The diagram below illustrate a signed SPL image layout: + + ------- +-----------------------------+ <-- *start + ^ | Image Vector Table | + | +-----------------------------+ <-- *boot_data + | | Boot Data | + | +-----------------------------+ + Signed | | Padding | + Data | +-----------------------------+ <-- *entry + | | | + | | SPL | + | | | + | +-----------------------------+ + v | Padding | + ------- +-----------------------------+ <-- *csf + | | + | Command Sequence File (CSF) | + | | + +-----------------------------+ + | Padding (optional) | + +-----------------------------+ + +The diagram below illustrate a signed u-boot-ivt.img image layout: + + ------- +-----------------------------+ <-- *load_address + ^ | | + | | | + | | u-boot.img | + Signed | | | + Data | | | + | +-----------------------------+ + | | Padding Next Boundary | + | +-----------------------------+ <-- *ivt + v | Image Vector Table | + ------- +-----------------------------+ <-- *csf + | | + | Command Sequence File (CSF) | + | | + +-----------------------------+ + | Padding (optional) | + +-----------------------------+ + +1.2 Enabling the secure boot support +------------------------------------- + +The first step is to generate an U-Boot image supporting the HAB features +mentioned above, this can be achieved by adding CONFIG_SECURE_BOOT to the +build configuration: + +- Defconfig: + + CONFIG_SECURE_BOOT=y + +- Kconfig: + + ARM architecture -> Support i.MX HAB features + +1.3 Creating the CSF description file +-------------------------------------- + +The CSF contains all the commands that the HAB executes during the secure +boot. These commands instruct the HAB code on which memory areas of the image +to authenticate, which keys to install, use and etc. + +CSF examples are available under doc/imx/habv4/csf_examples/ directory. + +Build logs containing the "Authenticate Data" parameters are available after +the U-Boot build, the example below is a log for mx6sabresd_defconfig target: + +- SPL build log: + + $ cat SPL.log + Image Type: Freescale IMX Boot Image + Image Ver: 2 (i.MX53/6/7 compatible) + Mode: DCD + Data Size: 69632 Bytes = 68.00 KiB = 0.07 MiB + Load Address: 00907420 + Entry Point: 00908000 + HAB Blocks: 0x00907400 0x00000000 0x0000ec00 + +- u-boot-ivt.img build log: + + $ cat u-boot-ivt.img.log + Image Name: U-Boot 2019.01-00003-g78ee492eb3 + Created: Mon Jan 14 17:58:10 2019 + Image Type: ARM U-Boot Firmware with HABv4 IVT (uncompressed) + Data Size: 458688 Bytes = 447.94 KiB = 0.44 MiB + Load Address: 17800000 + Entry Point: 00000000 + HAB Blocks: 0x177fffc0 0x0000 0x0006e020 + +As explained in section above the SPL is first authenticated by the ROM code +and the root of trust is extended to the U-Boot image, hence two CSF files are +necessary to completely sign a bootloader image. + +In "Authenticate Data" CSF command users can copy and past the output +addresses, the csf_uboot.txt can be used as example: + +- In csf_SPL.txt: + + Block = 0x00907400 0x00000000 0x0000ec00 "SPL" + +- In csf_uboot-ivt.txt: + + Block = 0x177fffc0 0x0000 0x0006e020 "u-boot-ivt.img" + +1.4 Signing the images +----------------------- + +The CST tool is used for singing the U-Boot binary and generating a CSF binary, +users should input the CSF description file created in the step above and +receive a CSF binary, which contains the CSF commands, SRK table, signatures +and certificates. + +- Create SPL CSF binary file: + + $ ./cst -i csf_SPL.txt -o csf_SPL.bin + +- Append CSF signature to the end of SPL image: + + $ cat SPL csf_SPL.bin > SPL-signed + +- Create U-Boot proper CSF binary file: + + $ ./cst -i csf_uboot-ivt.txt -o csf_uboot-ivt.bin + +- Append CSF signature to the end of U-Boot proper image: + + $ cat u-boot-ivt.img csf_uboot-ivt.bin > u-boot-signed.img + +The bootloader is signed and can be flashed into the boot media. + +1.5 Closing the device +----------------------- + +The procedure for closing the device is similar as in Non-SPL targets, for a +complete procedure please refer to section "1.5 Programming SRK Hash" in +mx6_mx7_secure_boot.txt document available under doc/imx/habv4/guides/ +directory. + +References: +[1] AN4581: "Secure Boot on i.MX 50, i.MX 53, i.MX 6 and i.MX 7 Series using + HABv4" - Rev 2.