7.27.7. NXP Platforms:

TRUSTED_BOARD_BOOT option can be enabled by specifying TRUSTED_BOARD_BOOT=1 on command line during make.

7.27.7.1. Bare-Minimum Preparation to run TBBR on NXP Platforms:

  • OTPMK(One Time Programable Key) needs to be burnt in fuses. – It is the 256 bit key that stores a secret value used by the NXP SEC 4.0 IP in Trusted or Secure mode.

    Note: It is primarily for the purpose of decrypting additional secrets stored in system non-volatile memory.

    – NXP CST tool gives an option to generate it.

    Use the below command from directory ‘cst’, with correct options.

    ./gen_otpmk_drbg
    
  • SRKH (Super Root Key Hash) needs to be burnt in fuses. – It is the 256 bit hash of the list of the public keys of the SRK key pair. – NXP CST tool gives an option to generate the RSA key pair and its hash.

    Use the below command from directory ‘cst’, with correct options.

    ./gen_keys
    

Refer fuse frovisioning readme ‘nxp-ls-fuse-prov.rst’ for steps to blow these keys.

7.27.7.2. Two options are provided for TRUSTED_BOARD_BOOT:

7.27.8. Option 1: CoT using X 509 certificates

  • This CoT is as provided by ARM.

  • To use this option user needs to specify mbedtld dir path in MBEDTLS_DIR.

  • To generate CSF header, path of CST repository needs to be specified as CST_DIR

  • CSF header is embedded to each of the BL2 image.

  • GENERATE_COT=1 adds the tool ‘cert_create’ to the build environment to generate: – X509 Certificates as (.crt) files. – X509 Pem key file as (.pem) files.

  • SAVE_KEYS=1 saves the keys and certificates, if GENERATE_COT=1. – For this to work, file name for cert and keys are provided as part of compilation or build command.

    — default file names will be used, incase not provided as part compilation or build command. — default folder ‘BUILD_PLAT’ will be used to store them.

  • ROTPK for x.509 certificates is generated and embedded in bl2.bin and verified as part of CoT by Boot ROM during secure boot.

  • Compilation steps:

All Images
make PLAT=$PLAT TRUSTED_BOARD_BOOT=1 GENERATE_COT=1 MBEDTLS_DIR=$MBEDTLS_PATH CST_DIR=$CST_DIR_PATH \
BOOT_MODE=<platform_supported_boot_mode> \
RCW=$RCW_BIN \
BL32=$TEE_BIN SPD=opteed\
BL33=$UBOOT_SECURE_BIN \
pbl \
fip
Additional FIP_DDR Image (For NXP platforms like lx2160a)
 make PLAT=$PLAT TRUSTED_BOARD_BOOT=1 GENERATE_COT=1 MBEDTLS_DIR=$MBEDTLS_PATH fip_ddr

Note: make target 'fip_ddr' should never be combine with other make target 'fip', 'pbl' & 'bl2'.

7.27.9. Option 2: CoT using NXP CSF headers.

  • This option is automatically selected when TRUSTED_BOARD_BOOT is set but MBEDTLS_DIR path is not specified.

  • CSF header is embedded to each of the BL31, BL32 and BL33 image.

  • To generate CSF header, path of CST repository needs to be specified as CST_DIR

  • Default input files for CSF header generation is added in this repo.

  • Default input file requires user to generate RSA key pair named – srk.pri, and – srk.pub, and add them in ATF repo. – These keys can be generated using gen_keys tool of CST.

  • To change the input file , user can use the options BL33_INPUT_FILE, BL32_INPUT_FILE, BL31_INPUT_FILE

  • There are 2 paths in secure boot flow : – Development Mode (sb_en in RCW = 1, SFP->OSPR, ITS = 0)

    — In this flow , even on ROTPK comparison failure, flow would continue. — However SNVS is transitioned to non-secure state

    – Production mode (SFP->OSPR, ITS = 1)

    — Any failure is fatal failure

  • Compilation steps:

All Images
make PLAT=$PLAT TRUSTED_BOARD_BOOT=1 CST_DIR=$CST_DIR_PATH \
BOOT_MODE=<platform_supported_boot_mode> \
RCW=$RCW_BIN \
BL32=$TEE_BIN SPD=opteed\
BL33=$UBOOT_SECURE_BIN \
pbl \
fip
Additional FIP_DDR Image (For NXP platforms like lx2160a)
make PLAT=$PLAT TRUSTED_BOARD_BOOT=1 CST_DIR=$CST_DIR_PATH fip_ddr
  • Compilation Steps with build option for generic image processing filters to prepend CSF header: – Generic image processing filters to prepend CSF header

    BL32_INPUT_FILE = < file name> BL33_INPUT_FILE = <file name>

    make PLAT=$PLAT TRUSTED_BOARD_BOOT=1 CST_DIR=$CST_DIR_PATH \
    BOOT_MODE=<platform_supported_boot_mode> \
    RCW=$RCW_BIN \
    BL32=$TEE_BIN SPD=opteed\
    BL33=$UBOOT_SECURE_BIN \
    BL33_INPUT_FILE = <ip file> \
    BL32_INPUT_FILE = <ip_file> \
    BL31_INPUT_FILE = <ip file> \
    pbl \
    fip
    

7.27.9.1. Deploy ATF Images

Same steps as mentioned in the readme “nxp-layerscape.rst”.

7.27.9.2. Verification to check if Secure state is achieved:

Platform

SNVS_HPSR_REG

SYS_SECURE_BIT(=value)

SYSTEM_SECURE_CONFIG_BIT(=value)

SSM_STATE

lx2160ardb or lx2160aqds or lx2162aqds

0x01E90014

15 ( = 1, BootROM Booted)

14-12 ( = 010 means Intent to Secure, ( = 000 Unsecure)

11-8 (=1111 means secure boot) (=1011 means Non-secure Boot)

  • Production mode (SFP->OSPR, ITS = 1) – Linux prompt will successfully come. if the TBBR is successful.

    — Else, Linux boot will be successful.

    – For secure-boot status, read SNVS Register $SNVS_HPSR_REG from u-boot prompt:

      md $SNVS_HPSR_REG
    
    Command Output:
        1e90014: 8000AF00
    
        In case it is read as 00000000, then read this register using jtag (in development mode only through CW tap).
                     +0       +4       +8       +C
        [0x01E90014] 8000AF00
    
  • Development Mode (sb_en in RCW = 1, SFP->OSPR, ITS = 0) – Refer the SoC specific table to read the register to interpret whether the secure boot is achieved or not. – Using JTAG (in development environment only, using CW tap):

    — For secure-boot status, read SNVS Register $SNVS_HPSR_REG

      ccs::display_regs 86 0x01E90014 4 0 1
    
    Command Output:
        Using the SAP chain position number 86, following is the output.
    
                     +0       +4       +8       +C
        [0x01E90014] 8000AF00
    
        Note: Chain position number will vary from one SoC to other SoC.
    
  • Interpretation of the value:

    – 0xA indicates BootROM booted, with intent to secure. – 0xF = secure boot, as SSM_STATE.