Date: Fri, 17 Mar 2017 22:24:25 -0700 Subject: Convert documentation to markdown --- docs/depthcharge/index.html | 362 -------------------------------------------- docs/depthcharge/index.md | 279 ++++++++++++++++++++++++++++++++++ 2 files changed, 279 insertions(+), 362 deletions(-) delete mode 100644 docs/depthcharge/index.html create mode 100644 docs/depthcharge/index.md (limited to 'docs/depthcharge') diff --git a/docs/depthcharge/index.html b/docs/depthcharge/index.html deleted file mode 100644 index 3088237e..00000000 --- a/docs/depthcharge/index.html +++ /dev/null @@ -1,362 +0,0 @@ - - - - - - - - - Depthcharge payload - - - - -

- -

Depthcharge payload

- -

- This section relates to the depthcharge payload used in libreboot. -

- -

- Or Back to main index. -

- -

CrOS security model
Developer mode screen -
-

Recovery mode screen -
- Recovering from a bad state
- Enabling developer mode
-
Configuring verified boot parameters

- -

CrOS security model

- -

- 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. -

- -

- 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. -

- -

Developer mode screen

- -

- The developer mode screen can be accessed in depthcharge when developer mode is enabled.
- Developer mode can be enabled from the recovery mode screen. -

- -

- 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. -

- -

Holding the developer mode screen

- -

- 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

- -

- As instructed on the developer mode screen, a regular boot will happen 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

- -

- Depthcharge allows booting from different mediums, when they are allowed (see configuring verified boot parameters to enable or disable boot mediums).
- As instructed on the developer mode screen, booting from various mediums can be triggered by pressing various key combinations: -

- -

Internal storage: Ctrl + D
External media: Ctrl + U (when enabled)
Legacy payload: Ctrl + L (when enabled)

- -

Showing device information

- -

- As instructed on the developer mode screen, showing device information 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.
-

- -

Warnings

- -

- The developer mode screen will show warnings when: - -

Booting kernels without verifying their signature is enabled
Booting from external media is enabled
Booting legacy payloads is enabled

- -

Recovery mode screen

- -

- The recovery mode screen can be accessed in depthcharge, by pressing Escape + Refresh + Power when the device is off. -

- -

- 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

- -

- 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.
- 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.
- 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).
- They are signed with Google's recovery keys, that are pre-installed on the device when it ships. -

- -

- 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. -

- -

Enabling developer mode

- -

- As instructed on the recovery mode screen, developer mode can be enabled by pressing Ctrl + D.
- Instructions to confirm enabling developer mode are then shown on screen. -

- -

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.
- These parameters can be modified with the crossystem tool, that requires sufficient privileges to access the verified boot non-volatile storage. -

- -

- crossystem relies on mosys, that is used to access the verified boot non-volatile storage on some devices. - crossystem and mosys are both free software and their source code is made available by Google: crossystem. mosys.
- These tools are not distributed along with Libreboot yet. However, they are preinstalled on the device, with ChromeOS. -

- -

- Some of these parameters have the potential of weakening the security 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 -
-
- External media boot: -
- - 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 -
-
- Default boot medium: -
- - Internal storage:
  - # crossystem dev_default_boot=disk -
- - External media:
  - # crossystem dev_default_boot=usb -
- - Legacy payload:
  - # crossystem dev_default_boot=legacy -
- -

- -

- 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 Commons; - - A copy of the license can be found at ../cc-by-sa-4.0.txt -

- -

- Updated versions of the license (when available) can be found at - https://creativecommons.org/licenses/by-sa/4.0/legalcode -

- -

- 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. -

- 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. -

- 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. -

- -

- - - diff --git a/docs/depthcharge/index.md b/docs/depthcharge/index.md new file mode 100644 index 00000000..60f4e78e --- /dev/null +++ b/docs/depthcharge/index.md @@ -0,0 +1,279 @@ +

+ +Depthcharge payload {#pagetop} +=================== + +This section relates to the depthcharge payload used in libreboot. + +Or [Back to main index](../). + +- [CrOS security model](#cros_security_model) +- [Developer mode screen](#developer_mode_screen) + - Holding the developer mode screen + - Booting normally + - Booting from different mediums + - Showing device information + - Warnings +- [Recovery mode screen](#recovery_mode_screen) + - [Recovering from a bad state](#recovering_bad_state) + - [Enabling developer mode](#enabling_developer_mode) +- [Configuring verified boot + parameters](#configuring_verified_boot_parameters) + +

+ +

+ +CrOS security model {#cros_security_model} +=================== + +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. + +

+ +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.\ +Developer mode can be enabled from the [recovery mode +screen](#recovery_mode_screen). + +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. + +

+ +Holding the developer mode screen {#holding_developer_mode_screen} +--------------------------------- + +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).\ +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).\ +As instructed on the developer mode screen, booting from various mediums +can be triggered by pressing various key combinations: + +- Internal storage: **Ctrl + D** +- 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**.\ +Various information is shown, including vboot non-volatile data, TPM +status, GBB flags and key hashes.\ + +

+ +

+ +Warnings +-------- + +The developer mode screen will show warnings when: + +- Booting kernels without verifying their signature is enabled +- Booting from external media is enabled +- Booting legacy payloads is enabled + +

+ +

+ +Recovery mode screen {#recovery_mode_screen} +==================== + +The recovery mode screen can be accessed in depthcharge, by pressing +**Escape + Refresh + Power** when the device is off. + +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.\ +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.\ +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).\ +They are signed with Google\'s recovery keys, that are pre-installed on +the device when it ships. + +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. + +

+ +

+ +Enabling developer mode {#enabling_developer_mode} +----------------------- + +As instructed on the recovery mode screen, developer mode can be enabled +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.\ +These parameters can be modified with the **crossystem** tool, that +requires sufficient privileges to access the verified boot non-volatile +storage. + +**crossystem** relies on **mosys**, that is used to access the verified +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/).\ +These tools are not distributed along with Libreboot yet. However, they +are preinstalled on the device, with ChromeOS. + +Some of these parameters have the potential of **weakening the security +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** +- External media boot: + - 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** +- Default boot medium: + - Internal storage:\ + \# **crossystem dev\_default\_boot=disk** + - External media:\ + \# **crossystem dev\_default\_boot=usb** + - Legacy payload:\ + \# **crossystem dev\_default\_boot=legacy** + +

+ +

+ +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 +Commons; A copy of the license can be found at +[../cc-by-sa-4.0.txt](../cc-by-sa-4.0.txt) + +Updated versions of the license (when available) can be found at + + +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. + +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. + +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. + +

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