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With the new 2021.04 we have a new version of Chromium OS boot, which supports sandbox, coral and coral-on-coreboot. Add documentation for this. Signed-off-by: Simon Glass <sjg@chromium.org> Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
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5.8 KiB
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204 lines
5.8 KiB
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.. SPDX-License-Identifier: GPL-2.0+
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.. Copyright 2020 Google LLC
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.. sectionauthor:: Simon Glass <sjg@chromium.org>
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Running U-Boot with Chromium OS verified boot
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=============================================
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Note: Once you use the source below you can obtain extra documentation with
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'make htmldocs'. See the 'Internal Documentation' link, under
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'Chromium OS-specific doc'.
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To obtain::
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git clone https://github.com/sjg20/u-boot.git
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cd u-boot
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git checkout cros-2021.04
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cd ..
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git clone https://chromium.googlesource.com/chromiumos/platform/vboot_reference
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cd vboot_reference
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git checkout 45964294
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# futility: updater: Correct output version for Snow
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To build for sandbox::
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UB=/tmp/b/chromeos_sandbox # U-Boot build directory
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cd u-boot
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make O=$UB chromeos_sandbox_defconfig
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make O=$UB -j20 -s VBOOT_SOURCE=/path/to/vboot_reference \
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MAKEFLAGS_VBOOT=DEBUG=1 QUIET=1
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Replace sandbox with another supported target.
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This produces $UB/image.bin which contains the firmware binaries in a SPI
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flash image.
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To run on sandbox::
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CROS=~/cosarm
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IMG=$CROS/src/build/images/coral/latest/chromiumos_image.bin
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$UB/tpl/u-boot-tpl -d $UB/u-boot.dtb.out \
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-L6 -c "host bind 0 $IMG; vboot go auto" \
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-l -w -s state.dtb -r -n -m $UB/ram
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$UB/tpl/u-boot-tpl -d $UB/u-boot.dtb.out -L6 -l \
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-c "host bind 0 $IMG; vboot go auto" -w -s $UB/state.dtb -r -n -m $UB/mem
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To run on other boards:
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- Install image.bin in the SPI flash of your device
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- Boot your system
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Sandbox
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-------
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Most Chromium OS development with U-Boot is undertaken using sandbox. There is
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a sandbox target available (chromeos_sandbox) which allows running U-Boot on
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a Linux machine completion with emulations of the display, TPM, disk, etc.
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Running sandbox starts TPL, which contains the first phase of vboot, providing
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a device tree and binding a Chromium OS disk image for use to find kernels
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(any Chromium OS image will do). It also saves driver state between U-Boot
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phases into state.dtb and will automatically ensure that memory is shared
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between all phases. TPL will jump to SPL and then on to U-Boot proper.
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It is possible to run with debugging on, e.g.::
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gdb --args $UB/tpl/u-boot-tpl -d ....
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Breakpoints can be set in any U-Boot phase. Overall this is a good debugging
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environment for new verified-boot features.
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Samus
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-----
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Basic support is available for samus, using the chromeos_samus target. If you
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have an em100, use::
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sudo em100 -s -c W25Q128FW -d $UB/image.bin -t -r
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to write the image and then boot samus (Power-Refresh).
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Boot flow
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---------
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Verified boot starts in TPL, which selects the A or B SPL, which in turn selects
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the A or B U-Boot. Then this jumps to the selected kernel. If anything goes
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wrong, the device reboots and the recovery SPL and U-Boot are used instead.
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More details are available here:
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https://www.chromium.org/chromium-os/chromiumos-design-docs/firmware-boot-and-recovery
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New uclasses
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------------
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Several uclasses are provided in cros/:
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UCLASS_CROS_AUX_FW
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Chrome OS auxiliary firmware
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UCLASS_CROS_FWSTORE
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Chrome OS firmware storage
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UCLASS_CROS_NVDATA
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Chrome OS non-volatile data device
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UCLASS_CROS_VBOOT_EC
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Chrome OS vboot EC operations
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UCLASS_CROS_VBOOT_FLAG
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Chrome OS verified boot flag
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The existing UCLASS_CROS_EC is also used.
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Commands
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--------
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A new 'vboot' command is provided to run particular vboot stages. The most
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useful command is 'vboot go auto', which continues where the last stage left
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off.
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Note that TPL and SPL do not supports commands as yet, so the vboot code is
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called directly from the SPL boot devices (BOOT_DEVICE_CROS_VBOOT). See
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cros_load_image_tpl() and cros_load_image_spl() which both call
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vboot_run_auto().
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Config options
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--------------
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The main option is CONFIG_CHROMEOS, which enables a wide array of other options
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so that the required features are present.
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Device-tree config
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------------------
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Various options are available which control the operation of verified boot.
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See cros/dts/bindings/config.txt for details. Most config is handled at run-
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time, although build-time config (with Kconfig) could also be added fairly
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easily.
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Porting to other hardware
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-------------------------
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A basic port to samus (Chromebook Pixel 2015) is in a basic working state,
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using the chromeos_samus target. Patches will likely be forthcoming in early
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2019. Ports to an ARM board and coreboot (for x86 Chromebooks) are in the
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dreaming state.
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Tests
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-----
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Chromium OS firmware has a very limited set of tests. The tests that originally
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existed in U-Boot were not brought over to coreboot or depthcharge.
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The U-Boot tests ('make check') do operate, but at present there are no
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Chromium OS tests available. These will hopefully come together over time. Of
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course the above sandbox feature provides a sort of functional test and can
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detect problems that affect the flow or particular vboot features.
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U-Boot without Chromium OS verified boot
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----------------------------------------
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The following script can be used to boot a Chrome OS image on coral. It is
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defined as the boot command in mainline::
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# Read the image header and obtain the address of the kernel
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# The offset 4f0 is defined by verified boot and may change for other
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# Chromebooks
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read mmc 2:2 100000 0 80; setexpr loader *001004f0;
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# Get the kernel size and calculate the number of blocks (0x200 bytes each)
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setexpr size *00100518; setexpr blocks $size / 200;
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# Read the full kernel and calculate the address of the setup block
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read mmc 2:2 100000 80 $blocks; setexpr setup $loader - 1000;
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# Locate the command line
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setexpr cmdline $loader - 2000;
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# Start the zboot process with the loaded kernel, setup block and cmdline
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zboot start 100000 0 0 0 $setup $cmdline;
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# Load the kernel, fix up the 'setup' block, dump information
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zboot load; zboot setup; zboot dump
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# Boot into Chrome OS
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zboot go
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7 October 2018
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