Hello,
I'm trying to make secure boot work on i.MX6 SABRE with SPL and u-boot-dtb.img files and I'm not sure how to do it.
I'm using the U-Boot vanilla master branch (2024.04-rc2) with the following configuration:
# Remove some stuff to not exceed file size limit $ cat <<EOF >> configs/mx6sabresd_defconfig CONFIG_BOOTMETH_EFILOADER=n CONFIG_CMD_NET=n CONFIG_NET=n EOF
# Enable secure boot $ cat <<EOF >> configs/mx6sabresd_defconfig CONFIG_IMX_HAB=y CONFIG_SPL_LOAD_FIT_ADDRESS=0x18000000 EOF
$ make ARCH=arm O=build mx6sabresd_defconfig
$ make ARCH=arm O=build
I have no issue to generate a working SPL-signed file following doc/imx/habv4/guides/mx6_mx7_spl_secure_boot.txt instructions.
doc/imx/habv4/guides/mx6_mx7_spl_secure_boot.txt only gives instructions to sign u-boot-ivt.img but this file doesn't contain device trees listed in CONFIG_OF_LIST as u-boot-dtb.img does and I need them.
NXP AN4581 lists 2 possible formats to sign additional images:
- Image format:
------- +-----------------------------+ <-- *load_address ^ | | | | | | | Image data | Signed | | | Data | | | | +-----------------------------+ | | Padding Next Boundary | | +-----------------------------+ <-- *ivt v | Image Vector Table | ------- +-----------------------------+ <-- *csf | | | Command Sequence File (CSF) | | | +-----------------------------+ | Padding (optional) | +-----------------------------+
- FIT image format:
------- +-----------------------------+ ------- ^ | | ^ | | | | | | FDT FIT | | | | | | Signed data | | | | | +-----------------------------+ | | | Padding Next Boundary | | | +-----------------------------+ | v | Image Vector Table | | ------- +-----------------------------+ | FIT image | | | | Command Sequence File (CSF) | | | | | +-----------------------------+ | | Padding (optional) | | ------- +-----------------------------+ | ^ | | | Signed data | | U-Boot | | v | | v ------- +-----------------------------+ -------
And as u-boot-dtb.img is a FIT image, I probably have to use the FIT image format, right?
I manually craft the signed FIT image using doc/imx/habv4/csf_examples/mx8m/csf.sh as reference and everything looks fine:
U-Boot SPL 2024.04-rc2-00025-g9e00b6993f-dirty (Feb 19 2024 - 13:17:31 +0100) >>SPL: board_init_r() spl_init Trying to boot from MMC1 fit read offset 11400, size=12800, dst=18000000, count=12800 spl_load_simple_fit_fix_load: ivt: 18001000 offset: 1000 size: 3060 spl_load_simple_fit_fix_load: ivt self: 18001000 hab fuse not enabled
Authenticate image from DDR location 0x18000000...
ivt_offset = 0x1000, ivt addr = 0x18001000 ivt entry = 0x18000000, dcd = 0x00000000, csf = 0x18001020 Dumping IVT .. @............ ........ ....... Dumping CSF Header ..PC...........P ................ .......<........ ...............8
Calling authenticate_image in ROM ivt_offset = 0x1000 start = 0x18000000 bytes = 0x3060 firmware: 'firmware-1' External data: dst=17800000, offset=3060, size=86138 Image OS is U-Boot fdt: 'fdt-1' Can't get 'load' property from FIT 0x18000000, node: offset 464, name fdt-1 (FDT_ERR_NOTFOUND) External data: dst=17886140, offset=89198, size=ac00 Can't get 'entry' property from FIT 0x18000000, node: offset 464, name fdt-1 (FDT_ERR_NOTFOUND) loadables: 'firmware-1' no string for index 1 Jumping to U-Boot... SPL malloc() used 0x0 bytes (0 KB) image entry point: 0x
U-Boot 2024.04-rc2-00025-g9e00b6993f-dirty (Feb 19 2024 - 13:17:31 +0100)
CPU: Freescale i.MX6Q rev1.2 996 MHz (running at 792 MHz) CPU: Automotive temperature grade (-40C to 125C) at 35C Reset cause: POR Model: Freescale i.MX6 Quad SABRE Smart Device Board DRAM: 1 GiB Core: 94 devices, 23 uclasses, devicetree: separate WDT: Started watchdog@20c0000 with servicing every 1000ms (128s timeout) MMC: FSL_SDHC: 4, FSL_SDHC: 1, FSL_SDHC: 3 Loading Environment from MMC... *** Warning - bad CRC, using default environment
No panel detected: default to Hannstar-XGA Display: Hannstar-XGA (1024x768) In: serial Out: serial Err: serial SEC0: RNG instantiated Hit any key to stop autoboot: 0 => hab_status
Secure boot disabled
HAB Configuration: 0xf0, HAB State: 0x66 No HAB Events Found!
But as only the FDT part of the FIT image is checked through HAB, U-Boot and DTB are only protected by FIT image hashes, right?
Using fdtdump shows that crc32 is used as hash algorithm for FIT image which is a super weak one. I tried to pass another algo (sha256) using mkimage -o option but that doesn't work.
./tools/mkimage -f auto -A arm -T firmware -C none -O u-boot -a 0x17800000 -e 0x17800000 -p 0x0 -n "U-Boot 2024.04-rc2-00025-g9e00b6993f-dirty for mx6sabresd board" -E -b arch/arm/dts/imx6q-sabresd.dtb -b arch/arm/dts/imx6qp-sabresd.dtb -b arch/arm/dts/imx6dl-sabresd.dtb -d u-boot-nodtb.bin -o sha256 u-boot-dtb.img
Is there any way to change U-Boot FIT image hash?
I also try to use image format and force the HAB to verify the whole u-boot-dtb.img file by patching the FIT image size:
image_size=$(stat -tc %s u-boot-dtb.img) printf "00000004: %08x" "$image_size" | xxd -r - u-boot-dtb.img
SPL starts, authentication looks fine but the boot fails. Is there any chance to make it work or is it insane to try to use this format?
Regards,
Benjamin