diff options
Diffstat (limited to 'docs/depthcharge/index.html')
| -rw-r--r-- | docs/depthcharge/index.html | 362 |
1 files changed, 0 insertions, 362 deletions
diff --git a/docs/depthcharge/index.html b/docs/depthcharge/index.html deleted file mode 100644 index 210cde55..00000000 --- a/docs/depthcharge/index.html +++ /dev/null @@ -1,362 +0,0 @@ -<!DOCTYPE html> -<html> -<head> - <meta charset="utf-8"> - <meta name="viewport" content="width=device-width, initial-scale=1"> - - <style type="text/css"> - @import url('../css/main.css'); - </style> - - <title>Depthcharge payload</title> -</head> - -<body> - - <div class="section"> - - <h1 id="pagetop">Depthcharge payload</h1> - - <p> - This section relates to the depthcharge payload used in libreboot. - </p> - - <p> - Or <a href="../index.html">Back to main index</a>. - </p> - - <ul> - <li><a href="#cros_security_model">CrOS security model</a></li> - <li><a href="#developer_mode_screen">Developer mode screen</a> - <ul> - <li><a href="#holding_developer_mode_screen">Holding the developer mode screen</li> - <li><a href="#booting_normally">Booting normally</li> - <li><a href="#booting_different_mediums">Booting from different mediums</li> - <li><a href="#showing_device_information">Showing device information</li> - <li><a href="#warnings">Warnings</li> - </ul> - </li> - <li><a href="#recovery_mode_screen">Recovery mode screen</a> - <ul> - <li><a href="#recovering_bad_state">Recovering from a bad state</a></li> - <li><a href="#enabling_developer_mode">Enabling developer mode</a></li> - </ul> - </li> - <li><a href="#configuring_verified_boot_parameters">Configuring verified boot parameters</a></li> - </ul> - - </div> - - <div class="section"> - - <h1 id="cros_security_model">CrOS security model</h1> - - <p> - CrOS (Chromium OS/Chrome OS) devices such as Chromebooks implement a strict security model to ensure that these devices do not become 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. - </p> - - <div class="subsection"> - - <p> - 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 <a href="#configuring_verified_boot_parameters">configuring verified boot parameters</a>. - </p> - - </div> - - </div> - - <div class="section"> - - <h1 id="developer_mode_screen">Developer mode screen</h1> - - <p> - The developer mode screen can be accessed in depthcharge when developer mode is enabled.<br /> - Developer mode can be enabled from the <a href="#recovery_mode_screen">recovery mode screen</a>. - </p> - - <p> - It allows booting normally, booting from internal storage, booting from external media (when enabled), booting from legacy payload (when enabled), showing information about the device and disabling developer mode. - </p> - - <div class="subsection"> - - <h2 id="holding_developer_mode_screen">Holding the developer mode screen</h2> - - <p> - As instructed on the developer mode screen, the screen can be held by pressing <b>Ctrl + H</b> in the first 3 seconds after the screen is shown. - After that delay, depthcharge will resume booting normally. - </p> - - </div> - - <div class="subsection"> - - <h2 id="booting_normally">Booting normally</h2> - - <p> - As instructed on the developer mode screen, a regular boot will happen after <b>3 seconds</b> (if developer mode screen is not held).<br /> - The default boot medium (internal storage, external media, legacy payload) is shown on screen. - </p> - - </div> - - <div class="subsection"> - - <h2 id="booting_different_mediums">Booting from different mediums</h2> - - <p> - Depthcharge allows booting from different mediums, when they are allowed (see <a href="#configuring_verified_boot_parameters">configuring verified boot parameters</a> to enable or disable boot mediums).<br /> - As instructed on the developer mode screen, booting from various mediums can be triggered by pressing various key combinations: - </p> - - <ul> - <li>Internal storage: <b>Ctrl + D</b></li> - <li>External media: <b>Ctrl + U</b> (when enabled)</li> - <li>Legacy payload: <b>Ctrl + L</b> (when enabled)</li> - </ul> - - </div> - - <div class="subsection"> - - <h2 id="showing_device_information">Showing device information</h2> - - <p> - As instructed on the developer mode screen, showing device information can be triggered by pressing <b>Ctrl + I</b> or <b>Tab</b>.<br /> - Various information is shown, including vboot non-volatile data, TPM status, GBB flags and key hashes.<br /> - </p> - - </div> - - <div class="subsection"> - - <h2 id="warnings">Warnings</h2> - - <p> - The developer mode screen will show warnings when: - - <ul> - <li>Booting kernels without verifying their signature is enabled</li> - <li>Booting from external media is enabled</li> - <li>Booting legacy payloads is enabled</li> - </ul> - - </p> - - </div> - - </div> - - <div class="section"> - - <h1 id="recovery_mode_screen">Recovery mode screen</h1> - - <p> - The recovery mode screen can be accessed in depthcharge, by pressing <b>Escape + Refresh + Power</b> when the device is off. - </p> - - <p> - 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. - </p> - - <div class="subsection"> - - <h2 id="recovering_bad_state">Recovering from a bad state</h2> - - <p> - 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.<br /> - Recovery mode boots using only software located in write-protected memory, that is considered to be trusted and safe. - </p> - - <p> - 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. <br /> - Trusted recovery media are external media (USB drives, SD cards, etc) that hold a kernel signed with the recovery key. - </p> - - <p> - Google provides images of such recovery media for Chrome OS (which are not advised to users as they contain proprietary software). <br /> - They are signed with Google's recovery keys, that are pre-installed on the device when it ships. - </p> - - <p> - When replacing the full flash of the device, the pre-installed keys are 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. - </p> - - </div> - - <div class="subsection"> - - <h2 id="enabling_developer_mode">Enabling developer mode</h2> - - <p> - As instructed on the recovery mode screen, developer mode can be enabled by pressing <b>Ctrl + D</b>.<br /> - Instructions to confirm enabling developer mode are then shown on screen. - </p> - - </div> - - </div> - - <div class="section"> - - <h1 id="configuring_verified_boot_parameters">Configuring verified boot parameters</h1> - - <p> - 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.<br /> - These parameters can be modified with the <b>crossystem</b> tool, that requires sufficient privileges to access the verified boot non-volatile storage. - </p> - - <p> - <b>crossystem</b> relies on <b>mosys</b>, that is used to access the verified boot non-volatile storage on some devices. - <b>crossystem</b> and <b>mosys</b> are both free software and their source code is made available by Google: <a href="https://chromium.googlesource.com/chromiumos/platform/vboot_reference/">crossystem</a>. <a href="https://chromium.googlesource.com/chromiumos/platform/mosys/">mosys</a>.<br /> - These tools are not distributed along with Libreboot yet. However, they are preinstalled on the device, with ChromeOS. - </p> - - <p> - Some of these parameters have the potential of <b>weakening the security of the device</b>. - In particular, disabling kernels signature verification, external media boot and legacy payload boot can weaken the security of the device. - </p> - - <div class="subsection"> - - <p> - The following parameters can be configured: - </p> - - <ul> - - <li> - Kernels signature verification: - <ul> - - <li> - Enabled with:<br /> - # <b>crossystem dev_boot_signed_only=1</b> - </li> - - <li> - Disabled with:<br /> - # <b>crossystem dev_boot_signed_only=0</b> - </li> - - </ul> - </li> - - <li> - External media boot: - <ul> - - <li> - Enabled with:<br /> - # <b>crossystem dev_boot_usb=1</b> - </li> - - <li> - Disabled with:<br /> - # <b>crossystem dev_boot_usb=0</b> - </li> - - </ul> - </li> - - <li> - Legacy payload boot: - <ul> - - <li> - Enabled with:<br /> - # <b>crossystem dev_boot_legacy=1</b> - </li> - - <li> - Disabled with:<br /> - # <b>crossystem dev_boot_legacy=0</b> - </li> - - </ul> - </li> - - <li> - Default boot medium: - <ul> - - <li> - Internal storage:<br /> - # <b>crossystem dev_default_boot=disk</b> - </li> - - <li> - External media:<br /> - # <b>crossystem dev_default_boot=usb</b> - </li> - - <li> - Legacy payload:<br /> - # <b>crossystem dev_default_boot=legacy</b> - </li> - - </ul> - - </ul> - - </div> - - </div> - - <div class="section"> - - <p> - Copyright © 2015 Paul Kocialkowski <contact@paulk.fr><br/> - Permission is granted to copy, distribute and/or modify this document - under the terms of the GNU Free Documentation License, Version 1.3 - or any later version published by the Free Software Foundation; - with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. - A copy of the license can be found at <a href="../gfdl-1.3.txt">../gfdl-1.3.txt</a> - </p> - - <p> - Updated versions of the license (when available) can be found at - <a href="https://www.gnu.org/licenses/licenses.html">https://www.gnu.org/licenses/licenses.html</a> - </p> - - <p> - UNLESS OTHERWISE SEPARATELY UNDERTAKEN BY THE LICENSOR, TO THE - EXTENT POSSIBLE, THE LICENSOR OFFERS THE LICENSED MATERIAL AS-IS - AND AS-AVAILABLE, AND MAKES NO REPRESENTATIONS OR WARRANTIES OF - ANY KIND CONCERNING THE LICENSED MATERIAL, WHETHER EXPRESS, - IMPLIED, STATUTORY, OR OTHER. THIS INCLUDES, WITHOUT LIMITATION, - WARRANTIES OF TITLE, MERCHANTABILITY, FITNESS FOR A PARTICULAR - PURPOSE, NON-INFRINGEMENT, ABSENCE OF LATENT OR OTHER DEFECTS, - ACCURACY, OR THE PRESENCE OR ABSENCE OF ERRORS, WHETHER OR NOT - KNOWN OR DISCOVERABLE. WHERE DISCLAIMERS OF WARRANTIES ARE NOT - ALLOWED IN FULL OR IN PART, THIS DISCLAIMER MAY NOT APPLY TO YOU. - </p> - <p> - TO THE EXTENT POSSIBLE, IN NO EVENT WILL THE LICENSOR BE LIABLE - TO YOU ON ANY LEGAL THEORY (INCLUDING, WITHOUT LIMITATION, - NEGLIGENCE) OR OTHERWISE FOR ANY DIRECT, SPECIAL, INDIRECT, - INCIDENTAL, CONSEQUENTIAL, PUNITIVE, EXEMPLARY, OR OTHER LOSSES, - COSTS, EXPENSES, OR DAMAGES ARISING OUT OF THIS PUBLIC LICENSE OR - USE OF THE LICENSED MATERIAL, EVEN IF THE LICENSOR HAS BEEN - ADVISED OF THE POSSIBILITY OF SUCH LOSSES, COSTS, EXPENSES, OR - DAMAGES. WHERE A LIMITATION OF LIABILITY IS NOT ALLOWED IN FULL OR - IN PART, THIS LIMITATION MAY NOT APPLY TO YOU. - </p> - <p> - The disclaimer of warranties and limitation of liability provided - above shall be interpreted in a manner that, to the extent - possible, most closely approximates an absolute disclaimer and - waiver of all liability. - </p> - - </div> - -</body> -</html> |