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author | Alyssa Rosenzweig <alyssa@rosenzweig.io> | 2017-03-20 20:26:48 -0700 |
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committer | Alyssa Rosenzweig <alyssa@rosenzweig.io> | 2017-03-20 20:26:48 -0700 |
commit | a62fe03d3e84150e6186f57f53029d5a9abe3d7b (patch) | |
tree | 1a1276b32fcc5388165bd42b685c0d9e83380a7b /docs/depthcharge/index.md | |
parent | 07da8fb0c7d513bc73470b69be99f1add0cb95e5 (diff) | |
download | librebootfr-a62fe03d3e84150e6186f57f53029d5a9abe3d7b.tar.gz librebootfr-a62fe03d3e84150e6186f57f53029d5a9abe3d7b.zip |
undo breakages
Diffstat (limited to 'docs/depthcharge/index.md')
-rw-r--r-- | docs/depthcharge/index.md | 107 |
1 files changed, 59 insertions, 48 deletions
diff --git a/docs/depthcharge/index.md b/docs/depthcharge/index.md index da8126c7..c9682847 100644 --- a/docs/depthcharge/index.md +++ b/docs/depthcharge/index.md @@ -1,7 +1,10 @@ -% Depthcharge payload + +Depthcharge payload +=================== This section relates to the depthcharge payload used in libreboot. + - [CrOS security model](#cros_security_model) - [Developer mode screen](#developer_mode_screen) - Holding the developer mode screen @@ -15,6 +18,8 @@ This section relates to the depthcharge payload used in libreboot. - [Configuring verified boot parameters](#configuring_verified_boot_parameters) + + CrOS security model {#cros_security_model} =================== @@ -24,17 +29,20 @@ compromised, that is implemented as the verified boot (vboot) reference, most of which is executed within depthcharge. A detailed overview of the CrOS security model is available on the dedicated page. + In spite of the CrOS security model, depthcharge won't allow booting kernels without verifying their signature and booting from external media or legacy payload unless explicitly allowed: see [configuring verified boot parameters](#configuring_verified_boot_parameters). + + + Developer mode screen {#developer_mode_screen} ===================== The developer mode screen can be accessed in depthcharge when developer -mode is enabled. - +mode is enabled.\ Developer mode can be enabled from the [recovery mode screen](#recovery_mode_screen). @@ -43,6 +51,7 @@ external media (when enabled), booting from legacy payload (when enabled), showing information about the device and disabling developer mode. + Holding the developer mode screen {#holding_developer_mode_screen} --------------------------------- @@ -50,23 +59,25 @@ As instructed on the developer mode screen, the screen can be held by pressing **Ctrl + H** in the first 3 seconds after the screen is shown. After that delay, depthcharge will resume booting normally. + + Booting normally {#booting_normally} ---------------- As instructed on the developer mode screen, a regular boot will happen -after **3 seconds** (if developer mode screen is not held). - +after **3 seconds** (if developer mode screen is not held).\ The default boot medium (internal storage, external media, legacy payload) is shown on screen. + + Booting from different mediums {#booting_different_mediums} ------------------------------ Depthcharge allows booting from different mediums, when they are allowed (see [configuring verified boot parameters](#configuring_verified_boot_parameters) to enable or disable -boot mediums). - +boot mediums).\ As instructed on the developer mode screen, booting from various mediums can be triggered by pressing various key combinations: @@ -74,14 +85,17 @@ can be triggered by pressing various key combinations: - External media: **Ctrl + U** (when enabled) - Legacy payload: **Ctrl + L** (when enabled) + + Showing device information {#showing_device_information} -------------------------- As instructed on the developer mode screen, showing device information -can be triggered by pressing **Ctrl + I** or **Tab**. - +can be triggered by pressing **Ctrl + I** or **Tab**.\ Various information is shown, including vboot non-volatile data, TPM -status, GBB flags and key hashes. +status, GBB flags and key hashes.\ + + Warnings -------- @@ -92,6 +106,9 @@ The developer mode screen will show warnings when: - Booting from external media is enabled - Booting legacy payloads is enabled + + + Recovery mode screen {#recovery_mode_screen} ==================== @@ -102,27 +119,25 @@ It allows recovering the device from a bad state by booting from a trusted recovery media. When accessed with the device in a good state, it also allows enabling developer mode. + Recovering from a bad state {#recovering_bad_state} --------------------------- When the device fails to verify the signature of a piece of the boot software or when an error occurs, it is considered to be in a bad state -and will instruct the user to reboot to recovery mode. - +and will instruct the user to reboot to recovery mode.\ Recovery mode boots using only software located in write-protected memory, that is considered to be trusted and safe. Recovery mode then allows recovering the device by booting from a trusted recovery media, that is automatically detected when recovery mode starts. When no external media is found or when the recovery media -is invalid, instructions are shown on screen. - +is invalid, instructions are shown on screen.\ Trusted recovery media are external media (USB drives, SD cards, etc) that hold a kernel signed with the recovery key. Google provides images of such recovery media for Chrome OS (which are -not advised to users as they contain proprietary software). - +not advised to users as they contain proprietary software).\ They are signed with Google's recovery keys, that are pre-installed on the device when it ships. @@ -131,22 +146,25 @@ replaced. When the recovery private key is available (e.g. when using self-generated keys), it can be used to sign a kernel for recovery purposes. + + Enabling developer mode {#enabling_developer_mode} ----------------------- As instructed on the recovery mode screen, developer mode can be enabled -by pressing **Ctrl + D**. - +by pressing **Ctrl + D**.\ Instructions to confirm enabling developer mode are then shown on screen. + + + Configuring verified boot parameters {#configuring_verified_boot_parameters} ==================================== Depthcharge's behavior relies on the verified boot (vboot) reference implementation, that can be configured with parameters stored in the -verified boot non-volatile storage. - +verified boot non-volatile storage.\ These parameters can be modified with the **crossystem** tool, that requires sufficient privileges to access the verified boot non-volatile storage. @@ -156,8 +174,7 @@ boot non-volatile storage on some devices. **crossystem** and **mosys** are both free software and their source code is made available by Google: [crossystem](https://chromium.googlesource.com/chromiumos/platform/vboot_reference/). -[mosys](https://chromium.googlesource.com/chromiumos/platform/mosys/). - +[mosys](https://chromium.googlesource.com/chromiumos/platform/mosys/).\ These tools are not distributed along with Libreboot yet. However, they are preinstalled on the device, with ChromeOS. @@ -166,42 +183,36 @@ of the device**. In particular, disabling kernels signature verification, external media boot and legacy payload boot can weaken the security of the device. + The following parameters can be configured: - Kernels signature verification: - - Enabled with: - - # **crossystem dev\_boot\_signed\_only=1** - - Disabled with: - - # **crossystem dev\_boot\_signed\_only=0** + - Enabled with:\ + \# **crossystem dev\_boot\_signed\_only=1** + - Disabled with:\ + \# **crossystem dev\_boot\_signed\_only=0** - External media boot: - - Enabled with: - - # **crossystem dev\_boot\_usb=1** - - Disabled with: - - # **crossystem dev\_boot\_usb=0** + - Enabled with:\ + \# **crossystem dev\_boot\_usb=1** + - Disabled with:\ + \# **crossystem dev\_boot\_usb=0** - Legacy payload boot: - - Enabled with: - - # **crossystem dev\_boot\_legacy=1** - - Disabled with: - - # **crossystem dev\_boot\_legacy=0** + - Enabled with:\ + \# **crossystem dev\_boot\_legacy=1** + - Disabled with:\ + \# **crossystem dev\_boot\_legacy=0** - Default boot medium: - - Internal storage: - - # **crossystem dev\_default\_boot=disk** - - External media: + - Internal storage:\ + \# **crossystem dev\_default\_boot=disk** + - External media:\ + \# **crossystem dev\_default\_boot=usb** + - Legacy payload:\ + \# **crossystem dev\_default\_boot=legacy** - # **crossystem dev\_default\_boot=usb** - - Legacy payload: - # **crossystem dev\_default\_boot=legacy** -Copyright © 2015 Paul Kocialkowski <contact@paulk.fr> +Copyright © 2015 Paul Kocialkowski <contact@paulk.fr>\ Permission is granted to copy, distribute and/or modify this document under the terms of the Creative Commons Attribution-ShareAlike 4.0 International license or any later version published by Creative |