docs/2_Architecture_Guides/2.2_Security_Blueprint/2_Secure_Boot/1.2.2.1_Image.md

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   3 title: Image
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   5   https://raw.githubusercontent.com/automotive-grade-linux/docs-sources/master/docs/security-blueprint/part-2/1-Image.md
   6 ---
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   9
  10 # Image
  11
  12 ## Image selection
  13
  14 The boot process shall be uninterruptible and shall irrevocably boot the image
  15 as specified in the boot environment.
  16
  17 In U-Boot set the "_bootdelay_" environment variable and/or define
  18 `CONFIG_BOOTDELAY` to _-2_.
  19
  20 <!-- section-config -->
  21
  22 Domain                 | _Variable_ / `Config` name | `Value`
  23 ---------------------- | -------------------------- | -------
  24 Boot-Image-Selection-1 | `CONFIG_BOOTDELAY`         | `-2`
  25 Boot-Image-Selection-2 | _bootdelay_                | `-2`
  26
  27 <!-- end-section-config -->
  28
  29 --------------------------------------------------------------------------------
  30
  31 ## Image authenticity
  32
  33 It shall not be possible to boot from an unverified image. The secure boot
  34 feature in U-Boot shall be enabled. The secure boot feature is available from
  35 U-Boot 2013.07 version. To enable the secure boot feature, enable the following
  36 features:
  37
  38 ```
  39 CONFIG_FIT: Enables support for Flat Image Tree (FIT) uImage format.
  40 CONFIG_FIT_SIGNATURE: Enables signature verification of FIT images.
  41 CONFIG_RSA: Enables RSA algorithm used for FIT image verification.
  42 CONFIG_OF_CONTROL: Enables Flattened Device Tree (FDT) configuration.
  43 CONFIG_OF_SEPARATE: Enables separate build of u-Boot from the device tree.
  44 CONFIG_DEFAULT_DEVICE_TREE: Specifies the default Device Tree used for the run-time configuration of U-Boot.
  45 ```
  46
  47 Generate the U-Boot image with public keys to validate and load the image. It
  48 shall use RSA2048 and SHA256 for authentication.
  49
  50 <!-- section-config -->
  51
  52 Domain                    | `Config` name                | _State_
  53 ------------------------- | ---------------------------- | --------
  54 Boot-Image-Authenticity-1 | `CONFIG_FIT`                 | _Enable_
  55 Boot-Image-Authenticity-2 | `CONFIG_FIT_SIGNATURE`       | _Enable_
  56 Boot-Image-Authenticity-3 | `CONFIG_RSA`                 | _Enable_
  57 Boot-Image-Authenticity-4 | `CONFIG_OF_CONTROL`          | _Enable_
  58 Boot-Image-Authenticity-5 | `CONFIG_OF_SEPARATE`         | _Enable_
  59 Boot-Image-Authenticity-6 | `CONFIG_DEFAULT_DEVICE_TREE` | _Enable_
  60
  61 <!-- end-section-config -->