7.19. NXP i.MX7 WaRP7

The Trusted Firmware-A port for the i.MX7Solo WaRP7 implements BL2 at EL3. The i.MX7S contains a BootROM with a High Assurance Boot (HAB) functionality. This functionality provides a mechanism for establishing a root-of-trust from the reset vector to the command-line in user-space.

7.19.1. Boot Flow

BootROM –> TF-A BL2 –> BL32(OP-TEE) –> BL33(U-Boot) –> Linux

In the WaRP7 port we encapsulate OP-TEE, DTB and U-Boot into a FIP. This FIP is expected and required

7.19.2. Build Instructions

We need to use a file generated by u-boot in order to generate a .imx image the BootROM will boot. It is therefore _required_ to build u-boot before TF-A and furthermore it is _recommended_ to use the mkimage in the u-boot/tools directory to generate the TF-A .imx image. U-Boot


git checkout -b rms-atf-optee-uboot linaro-mbl/rms-atf-optee-uboot
make warp7_bl33_defconfig;
make u-boot.imx arch=ARM CROSS_COMPILE=arm-linux-gnueabihf- OP-TEE


make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- PLATFORM=imx PLATFORM_FLAVOR=mx7swarp7 ARCH=arm CFG_PAGEABLE_ADDR=0 CFG_DT_ADDR=0x83000000 CFG_NS_ENTRY_ADDR=0x87800000 TF-A


The following commands assume that a directory exits in the top-level TFA build directory “fiptool_images”. “fiptool_images” contains

  • u-boot.bin The binary output from the u-boot instructions above

  • tee-header_v2.bin

  • tee-pager_v2.bin

  • tee-pageable_v2.bin Binary outputs from the previous OPTEE build steps

It is also assumed copy of mbedtls is available on the path path ../mbedtls

https://github.com/ARMmbed/mbedtls.git At the time of writing HEAD points to 0592ea772aee48ca1e6d9eb84eca8e143033d973

mkdir fiptool_images
cp /path/to/optee/out/arm-plat-imx/core/tee-header_v2.bin fiptool_images
cp /path/to/optee/out/arm-plat-imx/core/tee-pager_v2.bin fiptool_images
cp /path/to/optee/out/arm-plat-imx/core/tee-pageable_v2.bin fiptool_images

     NEED_BL32=yes BL32=fiptool_images/tee-header_v2.bin \
     BL32_EXTRA1=fiptool_images/tee-pager_v2.bin \
     BL32_EXTRA2=fiptool_images/tee-pageable_v2.bin \
     BL33=fiptool_images/u-boot.bin certificates all

/path/to/u-boot/tools/mkimage -n /path/to/u-boot/u-boot.cfgout -T imximage -e 0x9df00000 -d ./build/warp7/debug/bl2.bin ./build/warp7/debug/bl2.bin.imx FIP

cp /path/to/uboot/u-boot.bin fiptool_images
cp /path/to/linux/arch/boot/dts/imx7s-warp.dtb fiptool_images

tools/cert_create/cert_create -n --rot-key "build/warp7/debug/rot_key.pem" \
           --tfw-nvctr 0 \
           --ntfw-nvctr 0 \
           --trusted-key-cert fiptool_images/trusted-key-cert.key-crt \
           --tb-fw=build/warp7/debug/bl2.bin \
           --tb-fw-cert fiptool_images/trusted-boot-fw.key-crt\
           --tos-fw fiptool_images/tee-header_v2.bin \
           --tos-fw-cert fiptool_images/tee-header_v2.bin.crt \
           --tos-fw-key-cert fiptool_images/tee-header_v2.bin.key-crt \
           --tos-fw-extra1 fiptool_images/tee-pager_v2.bin \
           --tos-fw-extra2 fiptool_images/tee-pageable_v2.bin \
           --nt-fw fiptool_images/u-boot.bin \
           --nt-fw-cert fiptool_images/u-boot.bin.crt \
           --nt-fw-key-cert fiptool_images/u-boot.bin.key-crt \
           --hw-config fiptool_images/imx7s-warp.dtb

tools/fiptool/fiptool create --tos-fw fiptool_images/tee-header_v2.bin \
          --tos-fw-extra1 fiptool_images/tee-pager_v2.bin \
          --tos-fw-extra2 fiptool_images/tee-pageable_v2.bin \
          --nt-fw fiptool_images/u-boot.bin \
          --hw-config fiptool_images/imx7s-warp.dtb \
          --tos-fw-cert fiptool_images/tee-header_v2.bin.crt \
          --tos-fw-key-cert fiptool_images/tee-header_v2.bin.key-crt \
          --nt-fw-cert fiptool_images/u-boot.bin.crt \
          --nt-fw-key-cert fiptool_images/u-boot.bin.key-crt \
          --trusted-key-cert fiptool_images/trusted-key-cert.key-crt \
          --tb-fw-cert fiptool_images/trusted-boot-fw.key-crt warp7.fip

7.19.3. Deploy Images

First place the WaRP7 into UMS mode in u-boot this should produce an entry in /dev like /dev/disk/by-id/usb-Linux_UMS_disk_0_WaRP7-0xf42400d3000001d4-0:0

=> ums 0 mmc 0

Next flash bl2.imx and warp7.fip

bl2.imx is flashed @ 1024 bytes warp7.fip is flash @ 1048576 bytes

sudo dd if=bl2.bin.imx of=/dev/disk/by-id/usb-Linux_UMS_disk_0_WaRP7-0xf42400d3000001d4-0\:0 bs=512 seek=2 conv=notrunc
# Offset is 1MB 1048576 => 1048576 / 512 = 2048
sudo dd if=./warp7.fip of=/dev/disk/by-id/usb-Linux_UMS_disk_0_WaRP7-0xf42400d3000001d4-0\:0 bs=512 seek=2048 conv=notrunc

Remember to umount the USB device pefore proceeding

sudo umount /dev/disk/by-id/usb-Linux_UMS_disk_0_WaRP7-0xf42400d3000001d4-0\:0*

7.19.4. Signing BL2

A further step is to sign BL2.

The image_sign.sh and bl2_sign.csf files alluded to blow are available here.


It is suggested you use this script plus the example CSF file in order to avoid hard-coding data into your CSF files.

Download both “image_sign.sh” and “bl2_sign.csf” to your arm-trusted-firmware top-level directory.


#Remove temp
rm -rf ${TEMP}
mkdir ${TEMP}

# Generate IMX header
/path/to/u-boot/tools/mkimage -n u-boot.cfgout.warp7 -T imximage -e 0x9df00000 -d ./build/warp7/debug/bl2.bin ./build/warp7/debug/bl2.bin.imx > ${TEMP}/${BL2_IMX}.log

# Copy required items to $TEMP
cp build/warp7/debug/bl2.bin.imx ${TEMP}
cp ${CST_PATH}/keys/* ${TEMP}
cp ${CST_PATH}/crts/* ${TEMP}
cp ${BL2_CSF} ${TEMP}

# Generate signed BL2 image
./${SIGN} image_sign_mbl_binary ${TEMP} ${BL2_CSF} ${BL2_IMX} ${CST_BIN}

# Copy signed BL2 to top-level directory
cp ${TEMP}/${BL2_IMX}-signed .

The resulting bl2.bin.imx-signed can replace bl2.bin.imx in the Deploy Images section above, once done.

Suggested flow for verifying.

  1. Followed all previous steps above and verify a non-secure ATF boot

  2. Down the NXP Code Singing Tool

  3. Generate keys

  4. Program the fuses on your board

  5. Replace bl2.bin.imx with bl2.bin.imx-signed

  6. Verify inside u-boot that “hab_status” shows no events

  7. Subsequently close your board.

If you have HAB events @ step 6 - do not lock your board.

To get a good over-view of generating keys and programming the fuses on the board read “High Assurance Boot for Dummies” by Boundary Devices.