Immutable bootloader private key in zephyr

[Chris Burns]

In trying to use a private key file to sign the application image I'm running into an issue with the PEM file. I created a PEM file using the following command:

openssl ecparam -name prime256v1 -genkey -noout -out priv.pem

as documented here: https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/nrf/samples/bootloader/README.html

Then I modified my application's prj.conf file by adding these lines:

# Bootloader
CONFIG_SECURE_BOOT=y
CONFIG_SB_SIGNING_KEY_FILE="priv.pem"

The build output generates this error:

-- Using application from 'C:/Users/me/Repos/myproject'
Zephyr version: 2.0.99
-- Found PythonInterp: C:/Python37/python.exe (found suitable version "3.7.3", minimum required is "3.4")
-- Selected BOARD nrf9160_pca10090ns
-- Found west: C:/Python37/Scripts/west.exe (found suitable version "0.6.3", minimum required is "0.6.0")
-- Cache files will be written to: C:\Users\me\AppData\Local/.cache/zephyr
-- Loading C:/Users/me/Repos/ncs/zephyr/boards/arm/nrf9160_pca10090/nrf9160_pca10090ns.dts as base
-- Overlaying C:/Users/me/Repos/ncs/zephyr/dts/common/common.dts
-- Overlaying C:/Users/me/Repos/myproject/nrf9160_pca10090ns.overlay
Devicetree configuration written to C:/Users/me/Repos/myproject/build/zephyr/include/generated/generated_dts_board.conf

warning: TEST_RANDOM_GENERATOR (defined at subsys/random/Kconfig:8) was assigned the value 'y' but
got the value 'n'. You can check symbol information (including dependencies) in the 'menuconfig'
interface (see the Application Development Primer section of the manual), or in the Kconfig
reference at
http://docs.zephyrproject.org/latest/reference/kconfig/CONFIG_TEST_RANDOM_GENERATOR.html (which is
updated regularly from the master branch). See the 'Setting configuration values' section of the
Board Porting Guide as well.
Parsing Kconfig tree in C:/Users/me/Repos/myproject/Kconfig
Loaded configuration 'C:/Users/me/Repos/ncs/zephyr/boards/arm/nrf9160_pca10090/nrf9160_pca10090ns_defconfig'
Merged configuration 'C:/Users/me/Repos/myproject/prj.conf'
Configuration saved to 'C:/Users/me/Repos/myproject/build/zephyr/.config'
-- The C compiler identification is GNU 7.3.1
-- The CXX compiler identification is GNU 7.3.1
-- The ASM compiler identification is GNU
-- Found assembler: C:/gnuarmemb/bin/arm-none-eabi-gcc.exe
-- Using application from 'C:/Users/me/Repos/ncs/nrf/samples/nrf9160/spm'
Zephyr version: 2.0.99
Changed board to secure nrf9160_pca10090 (NOT NS)
USING OUT OF TREE BOARD
-- Loading C:/Users/me/Repos/ncs/zephyr/boards/arm/nrf9160_pca10090/nrf9160_pca10090.dts as base
-- Overlaying C:/Users/me/Repos/ncs/zephyr/dts/common/common.dts
-- Overlaying C:/Users/me/Repos/ncs/nrf/samples/nrf9160/spm/nrf9160_pca10090.overlay
Devicetree configuration written to C:/Users/me/Repos/myproject/build/spm/zephyr/include/generated/generated_dts_board.conf
Parsing Kconfig tree in C:/Users/me/Repos/ncs/zephyr/Kconfig
Loaded configuration 'C:/Users/me/Repos/ncs/zephyr/boards/arm/nrf9160_pca10090/nrf9160_pca10090_defconfig'
Merged configuration 'C:/Users/me/Repos/ncs/nrf/samples/nrf9160/spm/prj.conf'
Configuration saved to 'C:/Users/me/Repos/myproject/build/spm/zephyr/.config'
-- Using application from 'C:/Users/me/Repos/ncs/nrf/samples/bootloader'
Zephyr version: 2.0.99
Changed board to secure nrf9160_pca10090 (NOT NS)
-- Loading C:/Users/me/Repos/ncs/zephyr/boards/arm/nrf9160_pca10090/nrf9160_pca10090.dts as base
-- Overlaying C:/Users/me/Repos/ncs/zephyr/dts/common/common.dts
Devicetree configuration written to C:/Users/me/Repos/myproject/build/b0/zephyr/include/generated/generated_dts_board.conf
Parsing Kconfig tree in C:/Users/me/Repos/ncs/zephyr/Kconfig
Loaded configuration 'C:/Users/me/Repos/ncs/zephyr/boards/arm/nrf9160_pca10090/nrf9160_pca10090_defconfig'
Merged configuration 'C:/Users/me/Repos/ncs/nrf/samples/bootloader/prj.conf'
Configuration saved to 'C:/Users/me/Repos/myproject/build/b0/zephyr/.config'
CMake Error at C:/Users/me/Repos/ncs/nrf/subsys/bootloader/cmake/debug_keys.cmake:57 (message):
  Config points to non-existing PEM file 'priv.pem'
Call Stack (most recent call first):
  C:/Users/me/Repos/ncs/nrf/subsys/bootloader/image/CMakeLists.txt:67 (include)


-- Configuring incomplete, errors occurred!
See also "C:/Users/me/Repos/myproject/build/CMakeFiles/CMakeOutput.log".
See also "C:/Users/me/Repos/myproject/build/CMakeFiles/CMakeError.log".

The priv.pem file is in the same directory as my prj.conf file. What am I doing wrong that the build tools can't find it?

[shibshab]

I performed the following steps, and did not see any issue. Please let me know what you have done differently:

1. Jump to latest master (you should be able to do this on older commits as well)
2. West update <- The warning about the 'TEST_RANDOM_GENERATOR' might indicate that this step is not done properly
3. Use BOARD nrf9160_pca10090ns
4. Jump to zephyr/samples/hello_world
5. Run your openssl command
6. modify zephyr/samples/hello_world prj.conf by adding the two lines you mention above
7. cmake -GNinja -DBOARD=nrf9160_pca10090ns && ninja flash
8. Verify that hello world boots.

Also, the help text for the 'SB_SIGNING_KEY_FILE' explicitly states that the path shall be absolute. Note that for this case, the relative path provided by you also worked for me. 

Try to follow those steps, and let me know if/when it fails.

Edit: I see now that you are on windows. Please try to use the absolute path :)

[kk2mkk]

Hi shibshab,

I tried the above steps on nrf master, by specifying the private in absolute and relative path but the applicant failed to boot, with following error message.

# Bootloader
CONFIG_SECURE_BOOT=y
#CONFIG_SB_SIGNING_KEY_FILE="priv.pem"
CONFIG_SB_SIGNING_KEY_FILE="C:/Data/GIT/ncs/master/zephyr/samples/hello_world/priv.pem"

 

2020-10-12T13:50:30.809Z DEBUG modem << *** Booting Zephyr OS build v2.3.0-rc1-ncs1-3614-ga4ead9805140  ***
2020-10-12T13:50:30.817Z DEBUG modem << Attempting to boot slot 0.
2020-10-12T13:50:30.819Z DEBUG modem << Attempting to boot from address 0x8000.
2020-10-12T13:50:30.820Z DEBUG modem << Firwmare has been invalidated: 0x91020000.
2020-10-12T13:50:30.822Z DEBUG modem << Failed to validate, permanently invalidating!
2020-10-12T13:50:30.825Z DEBUG modem << Attempting to boot slot 1.
2020-10-12T13:50:30.827Z DEBUG modem << No fw_info struct found.
2020-10-12T13:50:30.831Z DEBUG modem << No bootable image found. Aborting boot.

thanks and regards

KK

[kk2mkk]

I think its nothing to do with the private key, even just enabling CONFIG_SECURE_BOOT=y doesn't work either

regards

KK

[shibshab]

Have performed a chip erase before flashing b0? `nrfjprog -e` 

[kk2mkk]

Yes i put extra caution in doing that step

[shibshab]

Are you building for a non-secure board? If so you should use MCUBoot as the single stage bootloader instead. B0 does not support non-secure apps as the next step in the bootloader chain.