esp-idf/components/bootloader/Kconfig.projbuild

menu "Bootloader config"
choice LOG_BOOTLOADER_LEVEL
   bool "Bootloader log verbosity"
   default LOG_BOOTLOADER_LEVEL_INFO
   help
       Specify how much output to see in bootloader logs.

config LOG_BOOTLOADER_LEVEL_NONE
   bool "No output"
config LOG_BOOTLOADER_LEVEL_ERROR
   bool "Error"
config LOG_BOOTLOADER_LEVEL_WARN
   bool "Warning"
config LOG_BOOTLOADER_LEVEL_INFO
   bool "Info"
config LOG_BOOTLOADER_LEVEL_DEBUG
   bool "Debug"
config LOG_BOOTLOADER_LEVEL_VERBOSE
   bool "Verbose"
endchoice

config LOG_BOOTLOADER_LEVEL
    int
    default 0 if LOG_BOOTLOADER_LEVEL_NONE
    default 1 if LOG_BOOTLOADER_LEVEL_ERROR
    default 2 if LOG_BOOTLOADER_LEVEL_WARN
    default 3 if LOG_BOOTLOADER_LEVEL_INFO
    default 4 if LOG_BOOTLOADER_LEVEL_DEBUG
    default 5 if LOG_BOOTLOADER_LEVEL_VERBOSE

config BOOTLOADER_SPI_WP_PIN
    int "SPI Flash WP Pin when customising pins via efuse (read help)"
    range 0 33
    default 7
    depends on FLASHMODE_QIO || FLASHMODE_QOUT
    help
        This value is ignored unless flash mode is set to QIO or QOUT *and* the SPI flash pins have been
        overriden by setting the efuses SPI_PAD_CONFIG_xxx.

        When this is the case, the Efuse config only defines 3 of the 4 Quad I/O data pins. The WP pin (aka ESP32
        pin "SD_DATA_3" or SPI flash pin "IO2") is not specified in Efuse. That pin number is compiled into the bootloader
        instead.

        The default value (GPIO 7) is correct for WP pin on ESP32-D2WD integrated flash.

choice BOOTLOADER_VDDSDIO_BOOST
    bool "VDDSDIO LDO voltage"
    default BOOTLOADER_VDDSDIO_BOOST_1_9V
    help
        If this option is enabled, and VDDSDIO LDO is set to 1.8V (using EFUSE
        or MTDI bootstrapping pin), bootloader will change LDO settings to
        output 1.9V instead. This helps prevent flash chip from browning out
        during flash programming operations.

        This option has no effect if VDDSDIO is set to 3.3V, or if the internal
        VDDSDIO regulator is disabled via efuse.

config BOOTLOADER_VDDSDIO_BOOST_1_8V
    bool "1.8V"
    depends on !ESPTOOLPY_FLASHFREQ_80M
config BOOTLOADER_VDDSDIO_BOOST_1_9V
    bool "1.9V"
endchoice

config BOOTLOADER_FACTORY_RESET
    bool "GPIO triggers factory reset"
    default N
    help
        Allows to reset the device to factory settings:
        - clear one or more data partitions;
        - boot from "factory" partition.
        The factory reset will occur if there is a GPIO input pulled low while device starts up.
        See settings below.

config BOOTLOADER_NUM_PIN_FACTORY_RESET
    int "Number of the GPIO input for factory reset"
    depends on BOOTLOADER_FACTORY_RESET
    range 0 39
    default 4
    help
        The selected GPIO will be configured as an input with internal pull-up enabled.
        To trigger a factory reset, this GPIO must be pulled low on reset.
        Note that GPIO34-39 do not have an internal pullup and an external one must be provided.

config BOOTLOADER_OTA_DATA_ERASE
    bool "Clear OTA data on factory reset (select factory partition)"
    depends on BOOTLOADER_FACTORY_RESET
    help
        The device will boot from "factory" partition (or OTA slot 0 if no factory partition is present) after a factory reset.

config BOOTLOADER_DATA_FACTORY_RESET
     string "Comma-separated names of partitions to clear on factory reset"
     depends on BOOTLOADER_FACTORY_RESET
     default "nvs"
     help
        Allows customers to select which data partitions will be erased while factory reset.
        
        Specify the names of partitions as a comma-delimited with optional spaces for readability. (Like this: "nvs, phy_init, ...")
        Make sure that the name specified in the partition table and here are the same. 
        Partitions of type "app" cannot be specified here.

config BOOTLOADER_APP_TEST
    bool "GPIO triggers boot from test app partition"
    default N
    help
        Allows to run the test app from "TEST" partition.
        A boot from "test" partition will occur if there is a GPIO input pulled low while device starts up.
        See settings below.

config BOOTLOADER_NUM_PIN_APP_TEST
    int "Number of the GPIO input to boot TEST partition"
    depends on BOOTLOADER_APP_TEST
    range 0 39
    default 18
    help
        The selected GPIO will be configured as an input with internal pull-up enabled.
        To trigger a test app, this GPIO must be pulled low on reset.
        After the GPIO input is deactivated and the device reboots, the old application will boot. 
        (factory or OTA[x]).
        Note that GPIO34-39 do not have an internal pullup and an external one must be provided.

config BOOTLOADER_HOLD_TIME_GPIO
    int "Hold time of GPIO for reset/test mode (seconds)"
    depends on BOOTLOADER_FACTORY_RESET || BOOTLOADER_APP_TEST
    default 5
    help
        The GPIO must be held low continuously for this period of time after reset 
        before a factory reset or test partition boot (as applicable) is performed.

endmenu  # Bootloader


menu "Security features"

config SECURE_BOOT_ENABLED
    bool "Enable secure boot in bootloader (READ DOCS FIRST)"
    default N
    help
        Build a bootloader which enables secure boot on first boot.

        Once enabled, secure boot will not boot a modified bootloader. The bootloader will only load a partition table or boot an app if the data has a verified digital signature. There are implications for reflashing updated apps once secure boot is enabled.

        When enabling secure boot, JTAG and ROM BASIC Interpreter are permanently disabled by default.

        Refer to https://docs.espressif.com/projects/esp-idf/en/latest/security/secure-boot.html before enabling.

choice SECURE_BOOTLOADER_MODE
    bool "Secure bootloader mode"
    depends on SECURE_BOOT_ENABLED
    default SECURE_BOOTLOADER_ONE_TIME_FLASH

config SECURE_BOOTLOADER_ONE_TIME_FLASH
       bool "One-time flash"
       help
           On first boot, the bootloader will generate a key which is not readable externally or by software. A digest is generated from the bootloader image itself. This digest will be verified on each subsequent boot.

           Enabling this option means that the bootloader cannot be changed after the first time it is booted.

config SECURE_BOOTLOADER_REFLASHABLE
    bool "Reflashable"
    help
        Generate a reusable secure bootloader key, derived (via SHA-256) from the secure boot signing key.

        This allows the secure bootloader to be re-flashed by anyone with access to the secure boot signing key.

        This option is less secure than one-time flash, because a leak of the digest key from one device allows reflashing of any device that uses it.

endchoice

config SECURE_BOOT_BUILD_SIGNED_BINARIES
     bool "Sign binaries during build"
     depends on SECURE_BOOT_ENABLED
     default y
     help
        Once secure boot is enabled, bootloader will only boot if partition table and app image are signed.

        If enabled, these binary files are signed as part of the build process. The file named in "Secure boot private signing key" will be used to sign the image.

        If disabled, unsigned app/partition data will be built. They must be signed manually using espsecure.py (for example, on a remote signing server.)

config SECURE_BOOT_SIGNING_KEY
     string "Secure boot private signing key"
     depends on SECURE_BOOT_BUILD_SIGNED_BINARIES
     default secure_boot_signing_key.pem
     help
        Path to the key file used to sign partition tables and app images for secure boot. Once secure boot is enabled, bootloader will only boot if partition table and app image are signed.

        Key file is an ECDSA private key (NIST256p curve) in PEM format.

        Path is evaluated relative to the project directory.

        You can generate a new signing key by running the following command:
        espsecure.py generate_signing_key secure_boot_signing_key.pem

        See docs/security/secure-boot.rst for details.

config SECURE_BOOT_VERIFICATION_KEY
    string "Secure boot public signature verification key"
    depends on SECURE_BOOT_ENABLED && !SECURE_BOOT_BUILD_SIGNED_BINARIES
    default signature_verification_key.bin
    help
       Path to a public key file used to verify signed images. This key is compiled into the bootloader,
       and may also be used to verify signatures on OTA images after download.

       Key file is in raw binary format, and can be extracted from a
       PEM formatted private key using the espsecure.py
       extract_public_key command.

       Refer to https://docs.espressif.com/projects/esp-idf/en/latest/security/secure-boot.html before enabling.

config SECURE_BOOT_INSECURE
    bool "Allow potentially insecure options"
    depends on SECURE_BOOT_ENABLED
    default N
    help
       You can disable some of the default protections offered by secure boot, in order to enable testing or a custom combination of security features.

       Only enable these options if you are very sure.

       Refer to https://docs.espressif.com/projects/esp-idf/en/latest/security/secure-boot.html before enabling.

config FLASH_ENCRYPTION_ENABLED
    bool "Enable flash encryption on boot (READ DOCS FIRST)"
    default N
    help
       If this option is set, flash contents will be encrypted by the bootloader on first boot.

       Note: After first boot, the system will be permanently encrypted. Re-flashing an encrypted
       system is complicated and not always possible.

       Read https://docs.espressif.com/projects/esp-idf/en/latest/security/flash-encryption.html before enabling.

config FLASH_ENCRYPTION_INSECURE
    bool "Allow potentially insecure options"
    depends on FLASH_ENCRYPTION_ENABLED
    default N
    help
       You can disable some of the default protections offered by flash encryption, in order to enable testing or a custom combination of security features.

       Only enable these options if you are very sure.

       Refer to docs/security/secure-boot.rst and docs/security/flash-encryption.rst for details.

menu "Potentially insecure options"
    visible if FLASH_ENCRYPTION_INSECURE || SECURE_BOOT_INSECURE

# NOTE: Options in this menu NEED to have SECURE_BOOT_INSECURE
# and/or FLASH_ENCRYPTION_INSECURE in "depends on", as the menu
# itself doesn't enable/disable its children (if it's not set,
# it's possible for the insecure menu to be disabled but the insecure option
# to remain on which is very bad.)

config SECURE_BOOT_ALLOW_ROM_BASIC
       bool "Leave ROM BASIC Interpreter available on reset"
       depends on SECURE_BOOT_INSECURE || FLASH_ENCRYPTION_INSECURE
       default N
       help
          By default, the BASIC ROM Console starts on reset if no valid bootloader is
          read from the flash.

          When either flash encryption or secure boot are enabled, the default is to
          disable this BASIC fallback mode permanently via efuse.

          If this option is set, this efuse is not burned and the BASIC ROM Console may
          remain accessible.  Only set this option in testing environments.

config SECURE_BOOT_ALLOW_JTAG
       bool "Allow JTAG Debugging"
       depends on SECURE_BOOT_INSECURE || FLASH_ENCRYPTION_INSECURE
       default N
       help
          If not set (default), the bootloader will permanently disable JTAG (across entire chip) on first boot when either secure boot or flash encryption is enabled.

          Setting this option leaves JTAG on for debugging, which negates all protections of flash encryption and some of the protections of secure boot.

          Only set this option in testing environments.

config SECURE_BOOT_ALLOW_SHORT_APP_PARTITION
       bool "Allow app partition length not 64KB aligned"
       depends on SECURE_BOOT_INSECURE
       help
           If not set (default), app partition size must be a multiple of 64KB. App images are padded to 64KB length, and the bootloader checks any trailing bytes after the signature (before the next 64KB boundary) have not been written. This is because flash cache maps entire 64KB pages into the address space. This prevents an attacker from appending unverified data after the app image in the flash, causing it to be mapped into the address space.

           Setting this option allows the app partition length to be unaligned, and disables padding of the app image to this length. It is generally not recommended to set this option, unless you have a legacy partitioning scheme which doesn't support 64KB aligned partition lengths.

config FLASH_ENCRYPTION_UART_BOOTLOADER_ALLOW_ENCRYPT
    bool "Leave UART bootloader encryption enabled"
    depends on FLASH_ENCRYPTION_INSECURE
    default N
    help
        If not set (default), the bootloader will permanently disable UART bootloader encryption access on first boot. If set, the UART bootloader will still be able to access hardware encryption.

        It is recommended to only set this option in testing environments.

config FLASH_ENCRYPTION_UART_BOOTLOADER_ALLOW_DECRYPT
    bool "Leave UART bootloader decryption enabled"
    depends on FLASH_ENCRYPTION_INSECURE
    default N
    help
        If not set (default), the bootloader will permanently disable UART bootloader decryption access on first boot. If set, the UART bootloader will still be able to access hardware decryption.

        Only set this option in testing environments. Setting this option allows complete bypass of flash encryption.

config FLASH_ENCRYPTION_UART_BOOTLOADER_ALLOW_CACHE
    bool "Leave UART bootloader flash cache enabled"
    depends on FLASH_ENCRYPTION_INSECURE
    default N
    help
        If not set (default), the bootloader will permanently disable UART bootloader flash cache access on first boot. If set, the UART bootloader will still be able to access the flash cache.

        Only set this option in testing environments.

config SECURE_BOOT_TEST_MODE
       bool "Secure boot test mode: don't permanently set any efuses"
       depends on SECURE_BOOT_INSECURE
       default N
       help
          If this option is set, all permanent secure boot changes (via Efuse) are disabled.

          Log output will state changes which would be applied, but they will not be.

          This option is for testing purposes only - it completely disables secure boot protection.


endmenu  # Potentially Insecure
endmenu  # Security features