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# 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.
<!-- config -->
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_
<!-- endconfig --> <!-- config -->
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_
<!-- endconfig -->
--------------------------------------------------------------------------------
## Disable all unused Network Interfaces
Only used network interfaces should be enabled.
Where possible, services should also be limited to those necessary.
<!-- config -->
Domain | Communication modes | _State_
-------------------- | -------------------- | ---------------------------------------------------------------------------------------------
Boot-Communication-1 | `Network interfaces` | Preferably _no network interface is allowed_, otherwise, restrict the services to those used.
<!-- endconfig -->
## Remove or Disable Unnecessary Services, Ports, and Devices
Restrict the `services`, `ports` and `devices` to those used.
<!-- config -->
Domain | Object | Recommendations
-------------------- | --------------------------------- | -------------------------------------------------------------
Boot-Communication-1 | `Services`, `ports` and `devices` | Restrict the `services`, `ports` and `devices` to those used.
<!-- endconfig -->
## 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.
<!-- config -->
Domain | `Command` name | _State_
-------------------------- | -------------- | ---------
Boot-Communication-Flash-1 | `do_nand` | _Disable_
<!-- endconfig -->
Similarly sboot should disable flash access support through command line if any.
|
