7.28.7. NXP Platforms:

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

7.28.7.1. 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.

7.28.7.2. Two options are provided for TRUSTED_BOARD_BOOT:

7.28.8. 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'.

7.28.9. 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

7.28.9.1. Deploy ATF Images

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

7.28.9.2. 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.