1README on how boot images are created for secure TI devices 2 3CONFIG_TI_SECURE_DEVICE: 4Secure TI devices require a boot image that is authenticated by ROM 5code to function. Without this, even JTAG remains locked and the 6device is essentially useless. In order to create a valid boot image for 7a secure device from TI, the initial public software image must be signed 8and combined with various headers, certificates, and other binary images. 9 10Information on the details on the complete boot image format can be obtained 11from Texas Instruments. The tools used to generate boot images for secure 12devices are part of a secure development package (SECDEV) that can be 13downloaded from: 14 15 http://www.ti.com/mysecuresoftware (login required) 16 17The secure development package is access controlled due to NDA and export 18control restrictions. Access must be requested and granted by TI before the 19package is viewable and downloadable. Contact TI, either online or by way 20of a local TI representative, to request access. 21 22Booting of U-Boot SPL 23===================== 24 25 When CONFIG_TI_SECURE_DEVICE is set, the U-Boot SPL build process 26 requires the presence and use of these tools in order to create a 27 viable boot image. The build process will look for the environment 28 variable TI_SECURE_DEV_PKG, which should be the path of the installed 29 SECDEV package. If the TI_SECURE_DEV_PKG variable is not defined or 30 if it is defined but doesn't point to a valid SECDEV package, a 31 warning is issued during the build to indicate that a final secure 32 bootable image was not created. 33 34 Within the SECDEV package exists an image creation script: 35 36 ${TI_SECURE_DEV_PKG}/scripts/create-boot-image.sh 37 38 This is called as part of the SPL/u-boot build process. As the secure 39 boot image formats and requirements differ between secure SOC from TI, 40 the purpose of this script is to abstract these details as much as 41 possible. 42 43 The script is basically the only required interface to the TI SECDEV 44 package for creating a bootable SPL image for secure TI devices. 45 46 Invoking the script for AM43xx Secure Devices 47 ============================================= 48 49 create-boot-image.sh \ 50 <IMAGE_FLAG> <INPUT_FILE> <OUTPUT_FILE> <SPL_LOAD_ADDR> 51 52 <IMAGE_FLAG> is a value that specifies the type of the image to 53 generate OR the action the image generation tool will take. Valid 54 values are: 55 SPI_X-LOADER - Generates an image for SPI flash (byte 56 swapped) 57 XIP_X-LOADER - Generates a single stage u-boot for 58 NOR/QSPI XiP 59 ISSW - Generates an image for all other boot modes 60 61 <INPUT_FILE> is the full path and filename of the public world boot 62 loaderbinary file (depending on the boot media, this is usually 63 either u-boot-spl.bin or u-boot.bin). 64 65 <OUTPUT_FILE> is the full path and filename of the final secure 66 image. The output binary images should be used in place of the standard 67 non-secure binary images (see the platform-specific user's guides and 68 releases notes for how the non-secure images are typically used) 69 u-boot-spl_HS_SPI_X-LOADER - byte swapped boot image for SPI flash 70 u-boot_HS_XIP_X-LOADER - boot image for NOR or QSPI flash 71 u-boot-spl_HS_ISSW - boot image for all other boot media 72 73 <SPL_LOAD_ADDR> is the address at which SOC ROM should load the 74 <INPUT_FILE> 75 76 Invoking the script for DRA7xx/AM57xx Secure Devices 77 ==================================================== 78 79 create-boot-image.sh <IMAGE_TYPE> <INPUT_FILE> <OUTPUT_FILE> 80 81 <IMAGE_TYPE> is a value that specifies the type of the image to 82 generate OR the action the image generation tool will take. Valid 83 values are: 84 X-LOADER - Generates an image for NOR or QSPI boot modes 85 MLO - Generates an image for SD/MMC/eMMC boot modes 86 ULO - Generates an image for USB/UART peripheral boot modes 87 Note: ULO is not yet used by the u-boot build process 88 89 <INPUT_FILE> is the full path and filename of the public world boot 90 loader binary file (for this platform, this is always u-boot-spl.bin). 91 92 <OUTPUT_FILE> is the full path and filename of the final secure image. 93 The output binary images should be used in place of the standard 94 non-secure binary images (see the platform-specific user's guides 95 and releases notes for how the non-secure images are typically used) 96 u-boot-spl_HS_MLO - boot image for SD/MMC/eMMC. This image is 97 copied to a file named MLO, which is the name that 98 the device ROM bootloader requires for loading from 99 the FAT partition of an SD card (same as on 100 non-secure devices) 101 u-boot-spl_HS_X-LOADER - boot image for all other flash memories 102 including QSPI and NOR flash 103 104Booting of Primary U-Boot (u-boot.img) 105====================================== 106 107 The SPL image is responsible for loading the next stage boot loader, 108 which is the main u-boot image. For secure TI devices, the SPL will 109 be authenticated, as described above, as part of the particular 110 device's ROM boot process. In order to continue the secure boot 111 process, the authenticated SPL must authenticate the main u-boot 112 image that it loads. 113 114 The configurations for secure TI platforms are written to make the boot 115 process use the FIT image format for the u-boot.img (CONFIG_SPL_FRAMEWORK 116 and CONFIG_SPL_LOAD_FIT). With these configurations the binary 117 components that the SPL loads include a specific DTB image and u-boot 118 image. These DTB image may be one of many available to the boot 119 process. In order to secure these components so that they can be 120 authenticated by the SPL as they are loaded from the FIT image, the 121 build procedure for secure TI devices will secure these images before 122 they are integrated into the FIT image. When those images are extracted 123 from the FIT image at boot time, they are post-processed to verify that 124 they are still secure. The outlined security-related SPL post-processing 125 is enabled through the CONFIG_SPL_FIT_IMAGE_POST_PROCESS option which 126 must be enabled for the secure boot scheme to work. In order to allow 127 verifying proper operation of the secure boot chain in case of successful 128 authentication messages like "Authentication passed: CERT_U-BOOT-NOD" are 129 output by the SPL to the console for each blob that got extracted from the 130 FIT image. Note that the last part of this log message is the (truncated) 131 name of the signing certificate embedded into the blob that got processed. 132 133 The exact details of the how the images are secured is handled by the 134 SECDEV package. Within the SECDEV package exists a script to process 135 an input binary image: 136 137 ${TI_SECURE_DEV_PKG}/scripts/secure-binary-image.sh 138 139 This is called as part of the u-boot build process. As the secure 140 image formats and requirements can differ between the various secure 141 SOCs from TI, this script in the SECDEV package abstracts these 142 details. This script is essentially the only required interface to the 143 TI SECDEV package for creating a u-boot.img image for secure TI 144 devices. 145 146 The SPL/u-boot code contains calls to dedicated secure ROM functions 147 to perform the validation on the secured images. The details of the 148 interface to those functions is shown in the code. The summary 149 is that they are accessed by invoking an ARM secure monitor call to 150 the device's secure ROM (fixed read-only-memory that is secure and 151 only accessible when the ARM core is operating in the secure mode). 152 153 Invoking the secure-binary-image script for Secure Devices 154 ========================================================== 155 156 secure-binary-image.sh <INPUT_FILE> <OUTPUT_FILE> 157 158 <INPUT_FILE> is the full path and filename of the input binary image 159 160 <OUTPUT_FILE> is the full path and filename of the output secure image. 161