How to perform Secure Boot from Distribution package

Applicable for STM32MP13x lines, STM32MP15x lines

1 Article purpose[edit]

The purpose of this article is to explain how to perform a secure boot on a STM32MP device with Distribution package.
To perform this use-case you need to:

These steps are not reversible (you cannot reproduce in reverse).

Warning white.png Warning
Please take care to save the signature key generate which are put on STM32MP device. One time the signature are saved and the closed device it's not possible to change it

2 Creating signature key[edit]

For perform Secure Boot, you need to have binaries signed which a specific signature key.

If this signature key is already present STM32MP device, go directly to Distribution package with signed FIP.

For creating signature key, we need to use STM32MP KeyGen CLI Tool.

See KeyGen tool page for installation and command line options.
The minimal command to use is

 STM32MP_KeyGen_CLI -abs <output directory> -pwd <password> -n <number of key>

With:

  • <output directory> = patch to the generated private and public key files (privateKey.pem and publicKey*.pem)
  • <password> = Password of the private key. The password must contain 4 characters at least.
  • <number of key> = number of key pairs, 1 for STM32MP15 or 8 for stm32MP13
Warning white.png Warning
Please save the password associated to signature key and the files generated (publicKey*.pem and privateKey.pem),

they will be asked when you need to sign a binary.

2.1 Creating signature key for STM32MP15x lines More info.png[edit]

STM32MP15x lines More info.png device support only one couple of Signature key (Public key / Private Key)
Example:

 STM32MP_KeyGen_CLI -abs stm32mp15-key/ -pwd azerty -n 1
        -------------------------------------------------------------------
                        STM32MP Key Generator v1.0.0                              
        -------------------------------------------------------------------
 
  Prime256v1 curve is selected. 
  AES_256_cbc algorithm is selected for private key encryption
  Generating Prime256v1 keys... 
  Private key PEM file created 
  Public key PEM file created 
  public key hash file created 
  Keys packet 0 generated successfully.
  + public key:       /tmp/key/publicKey00.pem
  + private key:      /tmp/key/privateKey00.pem
  + public hash key:  /tmp/key/publicKeyHash00.bin
  ------------------------------------------------------------
  Hash of table of Hash of {algorithm + public Key} file generated successfully.
  + Hash Hash:  /tmp/key/publicKeysHashHashes.bin

2.2 Creating signature key for STM32MP13x lines Warning.png[edit]

STM32MP13x lines Warning.png device support 8 couples of Signature key (Public key / Private Key)
Example:

 STM32MP_KeyGen_CLI -abs stm32mp13-key/ -pwd azerty -n 8
       -------------------------------------------------------------------
                       STM32MP Key Generator v1.0.0                              
       -------------------------------------------------------------------

 Prime256v1 curve is selected. 
 AES_256_cbc algorithm is selected for private key encryption
 Generating Prime256v1 keys... 
 Private key PEM file created 
 Public key PEM file created 
 public key hash file created 
 Keys packet 0 generated successfully.
 + public key:       /tmp/key/publicKey00.pem
 + private key:      /tmp/key/privateKey00.pem
 + public hash key:  /tmp/key/publicKeyHash00.bin
 ------------------------------------------------------------
 AES_256_cbc algorithm is selected for private key encryption
 Generating Prime256v1 keys... 
 Private key PEM file created 
 Public key PEM file created 
 public key hash file created 
 Keys packet 1 generated successfully.
 + public key:       /tmp/key/publicKey01.pem
 + private key:      /tmp/key/privateKey01.pem
 + public hash key:  /tmp/key/publicKeyHash01.bin
 ------------------------------------------------------------
 AES_256_cbc algorithm is selected for private key encryption
 Generating Prime256v1 keys... 
 Private key PEM file created 
 Public key PEM file created 
 public key hash file created 
 Keys packet 2 generated successfully.
 + public key:       /tmp/key/publicKey02.pem
 + private key:      /tmp/key/privateKey02.pem
 + public hash key:  /tmp/key/publicKeyHash02.bin
 ------------------------------------------------------------
 AES_256_cbc algorithm is selected for private key encryption
 Generating Prime256v1 keys... 
 Private key PEM file created 
 Public key PEM file created 
 public key hash file created must be signed with 
 Keys packet 3 generated successfully.
 + public key:       /tmp/key/publicKey03.pem
 + private key:      /tmp/key/privateKey03.pem
 + public hash key:  /tmp/key/publicKeyHash03.bin
 ------------------------------------------------------------
 AES_256_cbc algorithm is selected for private key encryption
 Generating Prime256v1 keys... 
 Private key PEM file created 
 Public key PEM file created 
 public key hash file created 
 Keys packet 4 generated successfully.
 + public key:       /tmp/key/publicKey04.pem
 + private key:      /tmp/key/privateKey04.pem
 + public hash key:  /tmp/key/publicKeyHash04.bin
 ------------------------------------------------------------
 AES_256_cbc algorithm is selected for private key encryption
 Generating Prime256v1 keys... 
 Private key PEM file created 
 Public key PEM file created 
 public key hash file created 
 Keys packet 5 generated successfully.
 + public key:       /tmp/key/publicKey05.pem
 + private key:      /tmp/key/privateKey05.pem
 + public hash key:  /tmp/key/publicKeyHash05.bin
 ------------------------------------------------------------
 AES_256_cbc algorithm is selected for private key encryption
 Generating Prime256v1 keys... 
 Private key PEM file created 
 Public key PEM file created 
 public key hash file created 
 Keys packet 6 generated successfully.
 + public key:       /tmp/key/publicKey06.pemsoc
 + private key:      /tmp/key/privateKey06.pem
 + public hash key:  /tmp/key/publicKeyHash06.bin
 ------------------------------------------------------------
 AES_256_cbc algorithm is selected for private key encryption
 Generating Prime256v1 keys... 
 Private key PEM file created 
 Public key PEM file created 
 public key hash file created 
 Keys packet 7 generated successfully.
 + public key:       /tmp/key/publicKey07.pem
 + private key:      /tmp/key/privateKey07.pem
 + public hash key:  /tmp/key/publicKeyHash07.bin
 ------------------------------------------------------------
 Hash of table of Hash of {algorithm + public Key} file generated successfully.
 + Hash Hash:  /tmp/key/publicKeysHashHashes.bin

3 Put signature key on STM32MP[edit]

Info white.png Information
For Demonstration and TEST purpose, the signature key can be put on STM32MP device with a simple U-Boot command on development board.

For product purpose, it must be set on production step as described in the AN5510: Overview of the secure secret provisioning (SSP) on STM32MP1 Series.

3.1 Put hash key on device for STM32MP15x lines More info.png[edit]

To manually put the key on STM32MP device with U-Boot stm32key command, you need to:

  • Put the hash key file (publicKeyhash.bin), generated on previous section, on bootfs partition
  • Boot the board and stop on U-Boot console
  • Load hash public key in DDR
    for example, the hash key file is located on 8th partition of sdcard:
STM32MP> load mmc 0:8 0xc0000000 publicKeyhash.bin
  • Register hash public key
STM32MP> stm32key fuse 0xc0000000

For more information, see How to use U-Boot stm32key command.

3.2 Put hash key on device for STM32MP13x lines Warning.png[edit]

To manually put the key on STM32MP device with U-Boot stm32key command, you need to:

  • Put the hash key file (publicKeysHashHashes.bin), generated on previous section, on bootfs partition
  • Boot the board and stop on U-Boot console
  • Load hash public key in DDR
    for example, the hash key file is located on 8th partition of sdcard:
STM32MP> load mmc 0:8 0xc0000000 publicKeysHashHashes.bin
  • Register hash public key
STM32MP> stm32key fuse 0xc0000000

For more information, see How to use U-Boot stm32key command.

4 Distribution package with signed FIP[edit]

4.1 Pre-requisite[edit]

4.2 Generate Distribution package with signed binaries[edit]

Info white.png Information
With this step only FIP binaries are signed
  • source the environment of Distribution package
 source layers/meta-st/scripts/envsetup.sh

Select your DISTRO and your machine

  • Indicate where to found your Signature key

(in this example we are put the signature key on meta-st-stm32mp layer on key directory)
Add the following lines on your local.conf (on build directory)

For ST32MP15:

 echo 'FIP_SIGN_KEY = "key/stm32mp15/privateKey.pem" ' >> conf/local.conf 
 echo 'FIP_SIGN_KEY_EXTERNAL = "1" ' >> conf/local.conf 
 echo 'FIP_SIGN_KEY_PASS = "<password of signature key>" ' >> conf/local.conf
 echo 'TF_A_SIGN_ENABLE = "1" ' >> conf/local.conf 

For ST32MP13:

 echo 'FIP_SIGN_KEY = "key/stm32mp13/privateKey00.pem" ' >> conf/local.conf 
 echo 'FIP_SIGN_KEY_EXTERNAL = "1" ' >> conf/local.conf 
 echo 'FIP_SIGN_KEY_PASS = "<password of signature key>" ' >> conf/local.conf
 echo 'TF_A_SIGN_ENABLE = "1" ' >> conf/local.conf 

Request to sign the FIP file generated:

 echo 'FIP_SIGN_ENABLE = "1" ' >> conf/local.conf 
  • Compile your binaries

bitbake st-image-weston

On tmp-glibc/deploy/images/<machine name>/fip/ you will found the FIP file signed ready to be programmed on board.

5 Sign first stage bootloader binaries[edit]

The first stage bootloader binaries = TF-A BL2 are generated unsigned; we need to sign it manually with STM32MP_SigningTool_CLI.

For installation and command line options see Signing tool.

Info white.png Information
if you need to populate the FSBL binary via STM32CubeProgrammer, you need to also sign the serial boot TF-A BL2 loaded on memory

This tools is used to sign a binary with STM32 header, with the minimal options to sign the FSBL binary is:

 STM32MP_SigningTool_CLI -pubk <public key> -prvk  <private key> -pwd <password> -t fsbl -of <Option_Flags> -bin FSBL binary not signed>.stm32 -o <FSBL binary signed>.stm32

with:

  • <public key>= the path of the Private key files generated by KeyGen: publicKey*.pem, 1 for STM32MP15 and 8 for STM32MP13
  • <private key> = the path of the Public key file generated by KeyGen: privateKey.pem
  • <password> = pasword used by KeyGen to protect the key files
  • <Option_Flags> = the -of option is required only for STM32MP13, with 0x00000001 value

5.1 Signing first stage bootloader binaries for STM32MP15x lines More info.png[edit]

For SDCARD:

 STM32MP_SigningTool_CLI  -pubk <path to meta-st-stm32mp>key/stm32mp15/publicKey.pem -prvk  <path to meta-st-stm32mp>key/stm32mp15/privateKey.pem -pwd <password> -t ssbl -bin arm-trusted-firmware/tf-a-<board name>-sdcard.stm32 -o arm-trusted-firmware/tf-a-<board name>-sdcard_Signed.stm32

For EMMC:

 STM32MP_SigningTool_CLI  -pubk <path to meta-st-stm32mp>key/stm32mp15/publicKey.pem -prvk  <path to meta-st-stm32mp>key/stm32mp15/privateKey.pem -pwd <password> -t ssbl -bin arm-trusted-firmware/tf-a-<board name>-emmc.stm32 -o arm-trusted-firmware/tf-a-<board name>-emmc_Signed.stm32

For NAND:

 STM32MP_SigningTool_CLI  -pubk <path to meta-st-stm32mp>key/stm32mp15/publicKey.pem -prvk  <path to meta-st-stm32mp>key/stm32mp15/privateKey.pem -pwd <password> -t ssbl -bin arm-trusted-firmware/tf-a-<board name>-nand.stm32 -o arm-trusted-firmware/tf-a-<board name>-nand_Signed.stm32

For NOR:

 STM32MP_SigningTool_CLI  -pubk <path to meta-st-stm32mp>key/stm32mp15/publicKey.pem -prvk  <path to meta-st-stm32mp>key/stm32mp15/privateKey.pem -pwd <password> -t ssbl -bin arm-trusted-firmware/tf-a-<board name>-nor.stm32 -o arm-trusted-firmware/tf-a-<board name>-nor_Signed.stm32

For USB (used with STM32CubeProgrammer):

 STM32MP_SigningTool_CLI  -pubk <path to meta-st-stm32mp>key/stm32mp15/publicKey.pem -prvk  <path to meta-st-stm32mp>key/stm32mp15/privateKey.pem -pwd <password> -t ssbl -bin arm-trusted-firmware/tf-a-<board name>-usb.stm32 -o arm-trusted-firmware/tf-a-<board name>-usb_Signed.stm32

For UART (used with STM32CubeProgrammer):

 STM32MP_SigningTool_CLI  -pubk <path to meta-st-stm32mp>key/stm32mp15/publicKey.pem -prvk  <path to meta-st-stm32mp>key/stm32mp15/privateKey.pem -pwd <password> -t ssbl -bin arm-trusted-firmware/tf-a-<board name>-uart.stm32 -o arm-trusted-firmware/tf-a-<board name>-uart_Signed.stm32

5.2 Signing first stage bootloader binaries for STM32MP13x lines Warning.png[edit]

For SDCARD:

 STM32MP_SigningTool_CLI  -pubk <path to meta-st-stm32mp>key/stm32mp13/publicKey*.pem -prvk  <path to meta-st-stm32mp>key/stm32mp15/privateKey00.pem -pwd <password> -t ssbl -of 0x00000001 -bin arm-trusted-firmware/tf-a-<board name>-sdcard.stm32 -o arm-trusted-firmware/tf-a-<board name>-sdcard_Signed.stm32

For EMMC:

 STM32MP_SigningTool_CLI  -pubk <path to meta-st-stm32mp>key/stm32mp13/publicKey*.pem -prvk  <path to meta-st-stm32mp>key/stm32mp13/privateKey00.pem -pwd <password> -t ssbl -of 0x00000001 -bin arm-trusted-firmware/tf-a-<board name>-emmc.stm32 -o arm-trusted-firmware/tf-a-<board name>-emmc_Signed.stm32

For NAND:

 STM32MP_SigningTool_CLI  -pubk <path to meta-st-stm32mp>key/stm32mp13/publicKey*.pem -prvk  <path to meta-st-stm32mp>key/stm32mp13/privateKey00.pem -pwd <password> -t ssbl -of 0x00000001 -bin arm-trusted-firmware/tf-a-<board name>-nand.stm32 -o arm-trusted-firmware/tf-a-<board name>-nand_Signed.stm32

For NOR:

 STM32MP_SigningTool_CLI  -pubk <path to meta-st-stm32mp>key/stm32mp13/publicKey*.pem -prvk  <path to meta-st-stm32mp>key/stm32mp13/privateKey00.pem -pwd <password> -t ssbl -of 0x00000001 -bin arm-trusted-firmware/tf-a-<board name>-nor.stm32 -o arm-trusted-firmware/tf-a-<board name>-nor_Signed.stm32

For USB (used with STM32CubeProgrammer):

 STM32MP_SigningTool_CLI  -pubk <path to meta-st-stm32mp>key/stm32mp13/publicKey*.pem -prvk  <path to meta-st-stm32mp>key/stm32mp13/privateKey00.pem -pwd <password> -t ssbl -of 0x00000001 -bin arm-trusted-firmware/tf-a-<board name>-usb.stm32 -o arm-trusted-firmware/tf-a-<board name>-usb_Signed.stm32

For UART (used with STM32CubeProgrammer):

 STM32MP_SigningTool_CLI  -pubk <path to meta-st-stm32mp>key/stm32mp13/publicKey*.pem -prvk  <path to meta-st-stm32mp>key/stm32mp13/privateKey00.pem -pwd <password> -t ssbl -of 0x00000001 -bin arm-trusted-firmware/tf-a-<board name>-uart.stm32 -o arm-trusted-firmware/tf-a-<board name>-uart_Signed.stm32

6 Create FlashLayout for signed binaries[edit]

To populate the correct binaries on the board, you need to create a FlashLayout file with the signed binaries:

  • FSBL = tf-a-*_Signed.stm32
  • FIP = fip-*.bin

Example for FlashLayout_sdcard_stm32mp157f-dk2-optee.tsv:

#Opt	Id	Name	Type	IP	Offset	Binary
- 	0x01	fsbl-boot	Binary	none	0x0	arm-trusted-firmware/tf-a-stm32mp157f-dk2-usb.stm32
-	0x03	fip-boot	FIP	none	0x0	fip/fip-stm32mp157f-dk2-optee.bin
P	0x04	fsbl1	Binary	mmc0	0x00004400	arm-trusted-firmware/tf-a-stm32mp157f-dk2-sdcard.stm32
P	0x05	fsbl2	Binary	mmc0	0x00044400	arm-trusted-firmware/tf-a-stm32mp157f-dk2-sdcard.stm32
P	0x06	metadata1	Binary	mmc0	0x00084400	arm-trusted-firmware/metadata.bin
P	0x07	metadata2	Binary	mmc0	0x000C4400	arm-trusted-firmware/metadata.bin 
P	0x08	fip-a	FIP	mmc0	0x00104400	fip/fip-stm32mp157f-dk2-optee.bin
PED	0x09	fip-b	FIP	mmc0	0x00504400	none
PED	0x0A	u-boot-env	Binary	mmc0	0x00904400	none
P	0x10	bootfs	System	mmc0	0x00984400	st-image-bootfs-openstlinux-weston-stm32mp1.ext4
P	0x11	vendorfs	FileSystem	mmc0	0x04984400	st-image-vendorfs-openstlinux-weston-stm32mp1.ext4
P	0x12	rootfs	FileSystem	mmc0	0x05984400	st-image-weston-openstlinux-weston-stm32mp1.ext4
P	0x13	userfs	FileSystem	mmc0	0x33984400	st-image-userfs-openstlinux-weston-stm32mp1.ext4

You need to update the fsbl1-boot, fip-boot, fsbl1, fsbl2 and fip partitions.
Result:

#Opt	Id	Name	Type	IP	Offset	Binary
- 	0x01	fsbl-boot	Binary	none	0x0	arm-trusted-firmware/tf-a-stm32mp157f-dk2-usb_Signed.stm32
-	0x03	fip-boot	FIP	none	0x0	fip/fip-stm32mp157f-dk2-optee_Signed.bin
P	0x04	fsbl1	Binary	mmc0	0x00004400	arm-trusted-firmware/tf-a-stm32mp157f-dk2- sdcard_Signed.stm32
P	0x05	fsbl2	Binary	mmc0	0x00044400	arm-trusted-firmware/tf-a-stm32mp157f-dk2- sdcard_Signed.stm32
P	0x06	metadata1	Binary	mmc0	0x00084400	arm-trusted-firmware/metadata.bin
P	0x07	metadata2	Binary	mmc0	0x000C4400	arm-trusted-firmware/metadata.bin 
P	0x08	fip-a	FIP	mmc0	0x00104400	fip/fip-stm32mp157f-dk2-optee_Signed.bin
PED	0x09	fip-b	FIP	mmc0	0x00504400	none
PED	0x0A	u-boot-env	Binary	mmc0	0x00904400	none
P	0x10	bootfs	System	mmc0	0x00984400	st-image-bootfs-openstlinux-weston-stm32mp1.ext4
P	0x11	vendorfs	FileSystem	mmc0	0x04984400	st-image-vendorfs-openstlinux-weston-stm32mp1.ext4
P	0x12	rootfs	FileSystem	mmc0	0x05984400	st-image-weston-openstlinux-weston-stm32mp1.ext4
P	0x13	userfs	FileSystem	mmc0	0x33984400	st-image-userfs-openstlinux-weston-stm32mp1.ext4

7 Program and test[edit]

To populate the correct binaries on the board with STM32CubeProgrammer, you need to use the previous FlashLayout file with the signed binaries.

At boot time on board, you must check the two level of the secure boot: the ROM code secure boot validation and the TF-A BL2 trusted board boot validation.

8 Close the device[edit]

Info white.png Information
For Demonstration and TEST purpose, the STM32MP device can be closed with a simple U-Boot command on development board. For product purpose, it must be set on production step as described in the AN5510: Overview of the secure secret provisioning (SSP) on STM32MP1 Series.

For more information, see How to secure STM32 MPU.

Warning white.png Warning
Please take care to close the device only if the previous authentication test succeed, otherwise the chip will be bricked and could not be used anymore

In U-Boot console:

 STM32MP> stm32key close

For more information, see How to use U-Boot stm32key command.

As soon as the device is closed, and it is irreversible operation, the user is forced to use only signed images.

Warning white.png Warning
This must not be done on STM32MP13 or STM32MP15 part numbers without Secure boot enabled, otherwise the chip will be bricked and could not be used anymore

9 References[edit]