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diff --git a/docs/3_Architecture_Guides/2_Security_Blueprint/3_Secure_Boot.md b/docs/3_Architecture_Guides/2_Security_Blueprint/3_Secure_Boot.md deleted file mode 100644 index cdaa84c..0000000 --- a/docs/3_Architecture_Guides/2_Security_Blueprint/3_Secure_Boot.md +++ /dev/null @@ -1,261 +0,0 @@ ---- -title: Secure Boot ---- - -Domain | Improvement ---------------- | ---------------------------------------------------- -Boot-Abstract-1 | More generic and add examples (The chain of trust). - -Secure boot refers to preventing malicious software applications and -“unauthorized” operating systems from loading during the system start-up -process. The goal is to protect users from rootkits and other low-level malware -attacks. Modern bootloaders come with features that can be used to enable secure -boot in the system. - -**Boot Hardening**: Steps/requirements to configure the boot sequence, in order -to restrict the device from executing anything other than the approved software -image. - -In this part, we will see a series of settings that will allow us to improve -security during boot phase. For the purposes of reference and explanation, we -are providing guidance on how to configure an embedded device that runs with a -3.10.17 Linux kernel. If the integrity is not checked or if a critical error -occurs, the system must boot on a very stable backup image. - -**Requirements**: These requirements must be met even if an alternative version -of the Linux kernel is chosen. - -**Recommendations**: Detailed best practices that should be applied in order to -secure a device. Although they are not currently listed as hard requirements, -they may be upgraded to requirements status in the future. In addition, specific -operators may change some of these recommendations into requirements based on -their specific needs and objectives. - -Domain | Improvement ---------------- | ------------------------------------------- -Boot-Abstract-1 | Review the definition of the "boot loader". - -**Boot loader**: The boot loader consists of the Primary boot loader residing in -**OTP** memory, sboot, U-Boot and Secure loader residing in external flash (NAND -or SPI/NOR flash memory). The CPU on power on or reset executes the primary boot -loader. The **OTP** primary boot loader makes the necessary initial system -configuration and then loads the secondary boot loader sboot from external flash -memory to ram memory. The sboot then loads the U-Boot along with the Secure -loader. U-Boot then verifies the Kernel/system image integrity, then loads the -Kernel/system image before passing control to it. - --------------------------------------------------------------------------------- - -## Acronyms and Abbreviations - -The following table lists the terms utilized within this part of the document. - -Acronyms or Abbreviations | Description -------------------------- | ----------------------------------------------------------------------- -_FUSE_ | **F**ilesystem in **U**ser**S**pac**E** -_OTP_ | **O**ne-**T**ime-**P**rogrammable -_DOCSIS_ | **D**ata **O**ver **C**able **S**ervice **I**nterface **S**pecification - -# Image - -## Image selection - -The boot process shall be uninterruptible and shall irrevocably boot the image -as specified in the boot environment. - -In U-Boot set the "_bootdelay_" environment variable and/or define -`CONFIG_BOOTDELAY` to _-2_. - -Domain | _Variable_ / `Config` name | `Value` ----------------------- | -------------------------- | ------- -Boot-Image-Selection-1 | `CONFIG_BOOTDELAY` | `-2` -Boot-Image-Selection-2 | _bootdelay_ | `-2` - --------------------------------------------------------------------------------- - -## Image authenticity - -It shall not be possible to boot from an unverified image. The secure boot -feature in U-Boot shall be enabled. The secure boot feature is available from -U-Boot 2013.07 version. To enable the secure boot feature, enable the following -features: - -```sh -CONFIG_FIT: Enables support for Flat Image Tree (FIT) uImage format. -CONFIG_FIT_SIGNATURE: Enables signature verification of FIT images. -CONFIG_RSA: Enables RSA algorithm used for FIT image verification. -CONFIG_OF_CONTROL: Enables Flattened Device Tree (FDT) configuration. -CONFIG_OF_SEPARATE: Enables separate build of u-Boot from the device tree. -CONFIG_DEFAULT_DEVICE_TREE: Specifies the default Device Tree used for the run-time configuration of U-Boot. -``` - -Generate the U-Boot image with public keys to validate and load the image. It -shall use RSA2048 and SHA256 for authentication. - -Domain | `Config` name | _State_ -------------------------- | ---------------------------- | -------- -Boot-Image-Authenticity-1 | `CONFIG_FIT` | _Enable_ -Boot-Image-Authenticity-2 | `CONFIG_FIT_SIGNATURE` | _Enable_ -Boot-Image-Authenticity-3 | `CONFIG_RSA` | _Enable_ -Boot-Image-Authenticity-4 | `CONFIG_OF_CONTROL` | _Enable_ -Boot-Image-Authenticity-5 | `CONFIG_OF_SEPARATE` | _Enable_ -Boot-Image-Authenticity-6 | `CONFIG_DEFAULT_DEVICE_TREE` | _Enable_ - -# Communication modes - -## Disable USB, Serial and DOCSIS Support - -To disable USB support in U-Boot, following config's shall not be defined: - -``` -CONFIG_CMD_USB: Enables basic USB support and the usb command. -CONFIG_USB_UHCI: Defines the lowlevel part. -CONFIG_USB_KEYBOARD: Enables the USB Keyboard. -CONFIG_USB_STORAGE: Enables the USB storage devices. -CONFIG_USB_HOST_ETHER: Enables USB Ethernet adapter support. -``` - -In addition, disable unnecessary communication modes like Ethernet, Serial -ports, DOCSIS in U-Boot and sboot that are not necessary. - -Linux Kernel support for USB should be compiled-out if not required. If it is -needed, the Linux Kernel should be configured to only enable the minimum -required USB devices. User-initiated USB-filesystems should be treated with -special care. Whether or not the filesystems are mounted in userspace -(**FUSE**), restricted mount options should be observed. - -Domain | Communication modes | _State_ --------------------- | ------------------------- | -------------------------------------------------------------------------------------------------------------------------------------- -Boot-Communication-1 | `USB` | _Disabled_ and _Compiled-out_ if not required. -Boot-Communication-2 | `USB` | Else, Kernel should be configured to only enable the minimum required USB devices and filesystems should be treated with special care. -Boot-Communication-3 | `Ethernet` | _Disabled_ -Boot-Communication-4 | U-boot and sboot `DOCSIS` | _Disabled_ -Boot-Communication-5 | `Serial ports` | _Disabled_ - -Domain | `Config` name | _State_ ------------------------- | ----------------------- | ------------- -Boot-Communication-USB-1 | `CONFIG_CMD_USB` | _Not defined_ -Boot-Communication-USB-2 | `CONFIG_USB_UHCI` | _Not defined_ -Boot-Communication-USB-3 | `CONFIG_USB_KEYBOARD` | _Not defined_ -Boot-Communication-USB-4 | `CONFIG_USB_STORAGE` | _Not defined_ -Boot-Communication-USB-5 | `CONFIG_USB_HOST_ETHER` | _Not defined_ - --------------------------------------------------------------------------------- - -## Disable all unused Network Interfaces - -Only used network interfaces should be enabled. Where possible, services should -also be limited to those necessary. - -Domain | Communication modes | _State_ --------------------- | -------------------- | --------------------------------------------------------------------------------------------- -Boot-Communication-1 | `Network interfaces` | Preferably _no network interface is allowed_, otherwise, restrict the services to those used. - -## Remove or Disable Unnecessary Services, Ports, and Devices - -Restrict the `services`, `ports` and `devices` to those used. - -Domain | Object | Recommendations --------------------- | --------------------------------- | ------------------------------------------------------------- -Boot-Communication-1 | `Services`, `ports` and `devices` | Restrict the `services`, `ports` and `devices` to those used. - -## Disable flash access - -**Recommendation**: - -In U-Boot following flash memory commands shall be disabled: - -**NAND**: Support for nand flash access available through `do_nand` has to be -disabled. - -Domain | `Command` name | _State_ --------------------------- | -------------- | --------- -Boot-Communication-Flash-1 | `do_nand` | _Disable_ - -Similarly sboot should disable flash access support through command line if any. - -# Consoles - -## Disable serial console - -Serial console output shall be disabled. To disable console output in U-Boot, -set the following macros: - -Domain | `Config` name | `Value` ----------------------- | --------------------------------------- | --------- -Boot-Consoles-Serial-1 | `CONFIG_SILENT_CONSOLE` | `Disable` -Boot-Consoles-Serial-2 | `CONFIG_SYS_DEVICE_NULLDEV` | `Disable` -Boot-Consoles-Serial-3 | `CONFIG_SILENT_CONSOLE_UPDATE_ON_RELOC` | `Disable` - -Domain | Improvement ---------------- | ------------------------------------ -Boot-Consoles-1 | Secure loader: No reference earlier? - -And set "**silent**" environment variable. For the Secure loader, disable the -traces by not defining the below macro: - -Domain | `Environment variable` name | _State_ ----------------------- | --------------------------- | ------------- -Boot-Consoles-Serial-1 | `INC_DEBUG_PRINT` | _Not defined_ - -For sboot proper configuration needs to be done to disable the serial console. - --------------------------------------------------------------------------------- - -## Immutable environment variables - -In U-Boot, ensure Kernel command line, boot commands, boot delay and other -environment variables are immutable. This will prevent side-loading of alternate -images, by restricting the boot selection to only the image in FLASH. - -The environment variables shall be part of the text region in U-Boot as default -environment variable and not in non-volatile memory. - -Remove configuration options related to non-volatile memory, such as: - -Domain | `Config` name | _State_ --------------------------- | ---------------------------- | --------- -Boot-Consoles-Variables-1 | `CONFIG_ENV_IS_IN_MMC` | `#undef` -Boot-Consoles-Variables-2 | `CONFIG_ENV_IS_IN_EEPROM` | `#undef` -Boot-Consoles-Variables-3 | `CONFIG_ENV_IS_IN_FLASH` | `#undef` -Boot-Consoles-Variables-4 | `CONFIG_ENV_IS_IN_DATAFLASH` | `#undef` -Boot-Consoles-Variables-5 | `CONFIG_ENV_IS_IN_FAT` | `#undef` -Boot-Consoles-Variables-6 | `CONFIG_ENV_IS_IN_NAND` | `#undef` -Boot-Consoles-Variables-7 | `CONFIG_ENV_IS_IN_NVRAM` | `#undef` -Boot-Consoles-Variables-8 | `CONFIG_ENV_IS_IN_ONENAND` | `#undef` -Boot-Consoles-Variables-9 | `CONFIG_ENV_IS_IN_SPI_FLASH` | `#undef` -Boot-Consoles-Variables-10 | `CONFIG_ENV_IS_IN_REMOTE` | `#undef` -Boot-Consoles-Variables-11 | `CONFIG_ENV_IS_IN_UBI` | `#undef` -Boot-Consoles-Variables-12 | `CONFIG_ENV_IS_NOWHERE` | `#define` - --------------------------------------------------------------------------------- - -## (Recommendation) Removal of memory dump commands - -In U-Boot, following commands shall be disabled to avoid memory dumps: - -``` -md : Memory Display command. -mm : Memory modify command - auto incrementing address. -nm : Memory modify command - constant address. -mw : Memory write. -cp : Memory copy. -mwc : Memory write cyclic. -mdc : Memory display cyclic. -mtest : Simple ram read/write test. -loopw : Infinite write loop on address range. -``` - -Domain | `Command` name | _State_ ------------------------ | -------------- | ---------- -Boot-Consoles-MemDump-1 | `md` | _Disabled_ -Boot-Consoles-MemDump-2 | `mm` | _Disabled_ -Boot-Consoles-MemDump-3 | `nm` | _Disabled_ -Boot-Consoles-MemDump-4 | `mw` | _Disabled_ -Boot-Consoles-MemDump-5 | `cp` | _Disabled_ -Boot-Consoles-MemDump-6 | `mwc` | _Disabled_ -Boot-Consoles-MemDump-7 | `mdc` | _Disabled_ -Boot-Consoles-MemDump-8 | `mtest` | _Disabled_ -Boot-Consoles-MemDump-9 | `loopw` | _Disabled_ - -Similarly, memory dump support shall be disabled from sboot.
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