bootboot/x86_64-cb

BOOTBOOT Coreboot x86_64 Implementation

See BOOTBOOT Protocol for common details.

Implements the BOOTBOOT Protocol as a coreboot payload. Must be compiled using the coreboot build environment.

Compilation

Step 1 - Install dependencies

First, install the coreboot dependencies: bison, build-essentials, curl, flex, git, gnat, libncurses5-dev, m4, zlib. Please refer to the linked doc for up-to-date list of dependencies.

Step 2 - Get coreboot

Download coreboot and its submodules

$ git clone https://review.coreboot.org/coreboot
$ cd coreboot
$ git submodule update --init

It is very important to initialize submodules, otherwise you won't be able to compile coreboot.

Step 3 - Create toolchain

This step could take a while. Replace $(nproc) with the number of CPU cores you have.

$ make crossgcc-i386 CPUS=$(nproc)

Step 4 - Configure

Now configure coreboot for your motherboard (or qemu) and BOOTBOOT.

$ make menuconfig
    select 'Mainboard' menu
    Beside 'Mainboard vendor' should be '(Emulation)'
    Beside 'Mainboard model' should be 'QEMU x86 i440fx/piix4'
    select 'Exit'
    select 'Devices' menu
    select 'Display' menu
    Beside 'Framebuffer mode' should be 'Linear "high-resolution" framebuffer'
    select 'Exit'
    select 'Exit'
    select 'Payload' menu
    select 'Add a Payload'
    choose 'BOOTBOOT'
    select 'Exit'
    select 'Exit'
    select 'Yes'

It is important to set the display to "linear framebuffer", because BOOTBOOT does not handle the legacy, non-portable VGA text mode. Sadly there's no way of configuring this in run-time with libpayload.

Step 5 - Build coreboot

$ make

Step 6 - Test the newly compiled ROM in QEMU

For more information, read the coreboot docs. In the images directory you can find a precompiled coreboot-x86.rom binary.

$ qemu-system-x86_64 -bios build/coreboot.rom -drive file=$(BOOTBOOT)/images/disk-x86.img,format=raw -serial stdio

Adding Initrd to ROM

To add an initrd into ROM, first you have to generate one. It can be an (optionally gzipped) tar, cpio, etc. archive. You can also create it using the mkbootimg utility:

$ ./mkbootimg myos.json initrd.bin

Then use the cbfstool utility in the coreboot repository to add the initrd image into the ROM image:

$ ./build/cbfstool build/coreboot.rom add -t raw -f $(BOOTBOOT)/initrd.bin -n bootboot/initrd

You can add a fallback environment configuration similarily (only used if environment cannot be loaded from the usual places):

$ ./build/cbfstool build/coreboot.rom add -t raw -f $(BOOTBOOT)/environment.txt -n bootboot/config

Obviously this can only work if libpayload was compiled with CONFIG_LP_CBFS=y. Without you can still place the initrd on a Flashmap partition named "INITRD" (however using the fmaptool and dealing with the fmd format is a rocket science).

Machine state

IRQs masked. GDT unspecified, but valid, IDT unset. SSE, SMP enabled. Code is running in supervisor mode in ring 0 on all cores.

Installation

Once you have compiled a coreboot ROM with the BOOTBOOT payload, you can flash the build/coreboot.rom file to your mainboard.

Limitations

• The CMOS nvram does not store timezone, so always GMT+0 returned in bootboot.timezone.
• Coreboot does not provide a way to set screen resolution, so "screen=" config option is not used.
• Only supports SHA-XOR-CBC, no AES