xref: /openbmc/u-boot/doc/README.ti-secure (revision 8662bea38e2779a45275a6ac13a378f9f989930a)

README on how boot images are created for secure TI devices

CONFIG_TI_SECURE_DEVICE:
Secure TI devices require a boot image that is authenticated by ROM
code to function. Without this, even JTAG remains locked and the
device is essentially useless. In order to create a valid boot image for
a secure device from TI, the initial public software image must be signed
and combined with various headers, certificates, and other binary images.

Information on the details on the complete boot image format can be obtained
from Texas Instruments. The tools used to generate boot images for secure
devices are part of a secure development package (SECDEV) that can be
downloaded from:

	http://www.ti.com/mysecuresoftware (login required)

The secure development package is access controlled due to NDA and export
control restrictions. Access must be requested and granted by TI before the
package is viewable and downloadable. Contact TI, either online or by way
of a local TI representative, to request access.

Booting of U-Boot SPL
=====================

	When CONFIG_TI_SECURE_DEVICE is set, the U-Boot SPL build process
	requires the presence and use of these tools in order to create a
	viable boot image. The build process will look for the environment
	variable TI_SECURE_DEV_PKG, which should be the path of the installed
	SECDEV package. If the TI_SECURE_DEV_PKG variable is not defined or
	if it is defined but doesn't point to a valid SECDEV package, a
	warning is issued during the build to indicate that a final secure
	bootable image was not created.

	Within the SECDEV package exists an image creation script:

	${TI_SECURE_DEV_PKG}/scripts/create-boot-image.sh

	This is called as part of the SPL/u-boot build process. As the secure
	boot image formats and requirements differ between secure SOC from TI,
	the purpose of this script is to abstract these details as much as
	possible.

	The script is basically the only required interface to the TI SECDEV
	package for creating a bootable SPL image for secure TI devices.

	Invoking the script for AM43xx Secure Devices
	=============================================

	create-boot-image.sh \
		<IMAGE_FLAG> <INPUT_FILE> <OUTPUT_FILE> <SPL_LOAD_ADDR>

	<IMAGE_FLAG> is a value that specifies the type of the image to
	generate OR the action the image generation tool will take. Valid
	values are:
		SPI_X-LOADER - Generates an image for SPI flash (byte
			swapped)
		XIP_X-LOADER - Generates a single stage u-boot for
			NOR/QSPI XiP
		ISSW - Generates an image for all other boot modes

	<INPUT_FILE> is the full path and filename of the public world boot
	loaderbinary file (depending on the boot media, this is usually
	either u-boot-spl.bin or u-boot.bin).

	<OUTPUT_FILE> is the full path and filename of the final secure
	image. The output binary images should be used in place of the standard
	non-secure binary images (see the platform-specific user's guides and
	releases notes for how the non-secure images are typically used)
	u-boot-spl_HS_SPI_X-LOADER - byte swapped boot image for SPI flash
	u-boot_HS_XIP_X-LOADER - boot image for NOR or QSPI flash
	u-boot-spl_HS_ISSW - boot image for all other boot media

	<SPL_LOAD_ADDR> is the address at which SOC ROM should load the
	<INPUT_FILE>

	Invoking the script for DRA7xx/AM57xx Secure Devices
	====================================================

	create-boot-image.sh <IMAGE_TYPE> <INPUT_FILE> <OUTPUT_FILE>

	<IMAGE_TYPE> is a value that specifies the type of the image to
	generate OR the action the image generation tool will take. Valid
	values are:
		X-LOADER - Generates an image for NOR or QSPI boot modes
		MLO - Generates an image for SD/MMC/eMMC boot modes
		ULO - Generates an image for USB/UART peripheral boot modes
		Note: ULO is not yet used by the u-boot build process

	<INPUT_FILE> is the full path and filename of the public world boot
	loader binary file (for this platform, this is always u-boot-spl.bin).

	<OUTPUT_FILE> is the full path and filename of the final secure image.
	The output binary images should be used in place of the standard
	non-secure binary images (see the platform-specific user's guides
	and releases notes for how the non-secure images are typically used)
	u-boot-spl_HS_MLO - boot image for SD/MMC/eMMC. This image is
		copied to a file named MLO, which is the name that
		the device ROM bootloader requires for loading from
		the FAT partition of an SD card (same as on
		non-secure devices)
	u-boot-spl_HS_X-LOADER - boot image for all other flash memories
		including QSPI and NOR flash

Booting of Primary U-Boot (u-boot.img)
======================================

	The SPL image is responsible for loading the next stage boot loader,
	which is the main u-boot image. For secure TI devices, the SPL will
	be authenticated, as described above, as part of the particular
	device's ROM boot process. In order to continue the secure boot
	process, the authenticated SPL must authenticate the main u-boot
	image that it loads.

	The configurations for secure TI platforms are written to make the boot
	process use the FIT image format for the u-boot.img (CONFIG_SPL_FRAMEWORK
	and CONFIG_SPL_LOAD_FIT). With these configurations the binary
	components that the SPL loads include a specific DTB image and u-boot
	image. These DTB image may be one of many available to the boot
	process. In order to secure these components so that they can be
	authenticated by the SPL as they are loaded from the FIT image,	the
	build procedure for secure TI devices will secure these images before
	they are integrated into the FIT image. When those images are extracted
	from the FIT image at boot time, they are post-processed to verify that
	they are still secure. The outlined security-related SPL post-processing
	is enabled through the CONFIG_SPL_FIT_IMAGE_POST_PROCESS option which
	must be enabled for the secure boot scheme to work. In order to allow
	verifying proper operation of the secure boot chain in case of successful
	authentication messages like "Authentication passed: CERT_U-BOOT-NOD" are
	output by the SPL to the console for each blob that got extracted from the
	FIT image. Note that the last part of this log message is the (truncated)
	name of the signing certificate embedded into the blob that got processed.

	The exact details of the how the images are secured is handled by the
	SECDEV package. Within the SECDEV package exists a script to process
	an input binary image:

	${TI_SECURE_DEV_PKG}/scripts/secure-binary-image.sh

	This is called as part of the u-boot build process. As the secure
	image formats and requirements can differ between the various secure
	SOCs from TI, this script in the SECDEV package abstracts these
	details. This script is essentially the only required interface to the
	TI SECDEV package for creating a u-boot.img image for secure TI
	devices.

	The SPL/u-boot code contains calls to dedicated secure ROM functions
	to perform the validation on the secured images. The details of the
	interface to those functions is shown in the code. The summary
	is that they are accessed by invoking an ARM secure monitor call to
	the device's secure ROM (fixed read-only-memory that is secure and
	only accessible when the ARM core is operating in the secure mode).

	Invoking the secure-binary-image script for Secure Devices
	==========================================================

	secure-binary-image.sh <INPUT_FILE> <OUTPUT_FILE>

	<INPUT_FILE> is the full path and filename of the input binary image

	<OUTPUT_FILE> is the full path and filename of the output secure image.