poky/documentation/dev-manual/securing-images.rst - mdmillerii/openbmc - Gitiles

 .. SPDX-License-Identifier: CC-BY-SA-2.0-UK

 Making Images More Secure
 *************************

 Security is of increasing concern for embedded devices. Consider the
 issues and problems discussed in just this sampling of work found across
 the Internet:

 -  *"*\ `Security Risks of Embedded
    Systems <https://www.schneier.com/blog/archives/2014/01/security_risks_9.html>`__\ *"*
    by Bruce Schneier

 -  *"*\ `Internet Census
    2012 <http://census2012.sourceforge.net/paper.html>`__\ *"* by Carna
    Botnet

 -  *"*\ `Security Issues for Embedded
    Devices <https://elinux.org/images/6/6f/Security-issues.pdf>`__\ *"*
    by Jake Edge

 When securing your image is of concern, there are steps, tools, and
 variables that you can consider to help you reach the security goals you
 need for your particular device. Not all situations are identical when
 it comes to making an image secure. Consequently, this section provides
 some guidance and suggestions for consideration when you want to make
 your image more secure.

 .. note::

    Because the security requirements and risks are different for every
    type of device, this section cannot provide a complete reference on
    securing your custom OS. It is strongly recommended that you also
    consult other sources of information on embedded Linux system
    hardening and on security.

 General Considerations
 ======================

 There are general considerations that help you create more secure images.
 You should consider the following suggestions to make your device
 more secure:

 -  Scan additional code you are adding to the system (e.g. application
    code) by using static analysis tools. Look for buffer overflows and
    other potential security problems.

 -  Pay particular attention to the security for any web-based
    administration interface.

    Web interfaces typically need to perform administrative functions and
    tend to need to run with elevated privileges. Thus, the consequences
    resulting from the interface's security becoming compromised can be
    serious. Look for common web vulnerabilities such as
    cross-site-scripting (XSS), unvalidated inputs, and so forth.

    As with system passwords, the default credentials for accessing a
    web-based interface should not be the same across all devices. This
    is particularly true if the interface is enabled by default as it can
    be assumed that many end-users will not change the credentials.

 -  Ensure you can update the software on the device to mitigate
    vulnerabilities discovered in the future. This consideration
    especially applies when your device is network-enabled.

 -  Regularly scan and apply fixes for CVE security issues affecting
    all software components in the product, see ":ref:`dev-manual/vulnerabilities:checking for vulnerabilities`".

 -  Regularly update your version of Poky and OE-Core from their upstream
    developers, e.g. to apply updates and security fixes from stable
    and LTS branches.

 -  Ensure you remove or disable debugging functionality before producing
    the final image. For information on how to do this, see the
    ":ref:`dev-manual/securing-images:considerations specific to the openembedded build system`"
    section.

 -  Ensure you have no network services listening that are not needed.

 -  Remove any software from the image that is not needed.

 -  Enable hardware support for secure boot functionality when your
    device supports this functionality.

 Security Flags
 ==============

 The Yocto Project has security flags that you can enable that help make
 your build output more secure. The security flags are in the
 ``meta/conf/distro/include/security_flags.inc`` file in your
 :term:`Source Directory` (e.g. ``poky``).

 .. note::

    Depending on the recipe, certain security flags are enabled and
    disabled by default.

 Use the following line in your ``local.conf`` file or in your custom
 distribution configuration file to enable the security compiler and
 linker flags for your build::

    require conf/distro/include/security_flags.inc

 Considerations Specific to the OpenEmbedded Build System
 ========================================================

 You can take some steps that are specific to the OpenEmbedded build
 system to make your images more secure:

 -  Ensure "debug-tweaks" is not one of your selected
    :term:`IMAGE_FEATURES`.
    When creating a new project, the default is to provide you with an
    initial ``local.conf`` file that enables this feature using the
    :term:`EXTRA_IMAGE_FEATURES`
    variable with the line::

       EXTRA_IMAGE_FEATURES = "debug-tweaks"

    To disable that feature, simply comment out that line in your
    ``local.conf`` file, or make sure :term:`IMAGE_FEATURES` does not contain
    "debug-tweaks" before producing your final image. Among other things,
    leaving this in place sets the root password as blank, which makes
    logging in for debugging or inspection easy during development but
    also means anyone can easily log in during production.

 -  It is possible to set a root password for the image and also to set
    passwords for any extra users you might add (e.g. administrative or
    service type users). When you set up passwords for multiple images or
    users, you should not duplicate passwords.

    To set up passwords, use the :ref:`ref-classes-extrausers` class, which
    is the preferred method. For an example on how to set up both root and
    user passwords, see the ":ref:`ref-classes-extrausers`" section.

    .. note::

       When adding extra user accounts or setting a root password, be
       cautious about setting the same password on every device. If you
       do this, and the password you have set is exposed, then every
       device is now potentially compromised. If you need this access but
       want to ensure security, consider setting a different, random
       password for each device. Typically, you do this as a separate
       step after you deploy the image onto the device.

 -  Consider enabling a Mandatory Access Control (MAC) framework such as
    SMACK or SELinux and tuning it appropriately for your device's usage.
    You can find more information in the
    :yocto_git:`meta-selinux </meta-selinux/>` layer.

 Tools for Hardening Your Image
 ==============================

 The Yocto Project provides tools for making your image more secure. You
 can find these tools in the ``meta-security`` layer of the
 :yocto_git:`Yocto Project Source Repositories <>`.
	.. SPDX-License-Identifier: CC-BY-SA-2.0-UK

	Making Images More Secure
	*************************

	Security is of increasing concern for embedded devices. Consider the
	issues and problems discussed in just this sampling of work found across
	the Internet:

	- "\ `Security Risks of Embedded
	Systems <https://www.schneier.com/blog/archives/2014/01/security_risks_9.html>`__\ "
	by Bruce Schneier

	- "\ `Internet Census
	2012 <http://census2012.sourceforge.net/paper.html>`__\ " by Carna
	Botnet

	- "\ `Security Issues for Embedded
	Devices <https://elinux.org/images/6/6f/Security-issues.pdf>`__\ "
	by Jake Edge

	When securing your image is of concern, there are steps, tools, and
	variables that you can consider to help you reach the security goals you
	need for your particular device. Not all situations are identical when
	it comes to making an image secure. Consequently, this section provides
	some guidance and suggestions for consideration when you want to make
	your image more secure.

	.. note::

	Because the security requirements and risks are different for every
	type of device, this section cannot provide a complete reference on
	securing your custom OS. It is strongly recommended that you also
	consult other sources of information on embedded Linux system
	hardening and on security.

	General Considerations
	======================

	There are general considerations that help you create more secure images.
	You should consider the following suggestions to make your device
	more secure:

	- Scan additional code you are adding to the system (e.g. application
	code) by using static analysis tools. Look for buffer overflows and
	other potential security problems.

	- Pay particular attention to the security for any web-based
	administration interface.

	Web interfaces typically need to perform administrative functions and
	tend to need to run with elevated privileges. Thus, the consequences
	resulting from the interface's security becoming compromised can be
	serious. Look for common web vulnerabilities such as
	cross-site-scripting (XSS), unvalidated inputs, and so forth.

	As with system passwords, the default credentials for accessing a
	web-based interface should not be the same across all devices. This
	is particularly true if the interface is enabled by default as it can
	be assumed that many end-users will not change the credentials.

	- Ensure you can update the software on the device to mitigate
	vulnerabilities discovered in the future. This consideration
	especially applies when your device is network-enabled.

	- Regularly scan and apply fixes for CVE security issues affecting
	all software components in the product, see ":ref:`dev-manual/vulnerabilities:checking for vulnerabilities`".

	- Regularly update your version of Poky and OE-Core from their upstream
	developers, e.g. to apply updates and security fixes from stable
	and LTS branches.

	- Ensure you remove or disable debugging functionality before producing
	the final image. For information on how to do this, see the
	":ref:`dev-manual/securing-images:considerations specific to the openembedded build system`"
	section.

	- Ensure you have no network services listening that are not needed.

	- Remove any software from the image that is not needed.

	- Enable hardware support for secure boot functionality when your
	device supports this functionality.

	Security Flags
	==============

	The Yocto Project has security flags that you can enable that help make
	your build output more secure. The security flags are in the
	``meta/conf/distro/include/security_flags.inc`` file in your
	:term:`Source Directory` (e.g. ``poky``).

	.. note::

	Depending on the recipe, certain security flags are enabled and
	disabled by default.

	Use the following line in your ``local.conf`` file or in your custom
	distribution configuration file to enable the security compiler and
	linker flags for your build::

	require conf/distro/include/security_flags.inc

	Considerations Specific to the OpenEmbedded Build System
	========================================================

	You can take some steps that are specific to the OpenEmbedded build
	system to make your images more secure:

	- Ensure "debug-tweaks" is not one of your selected
	:term:`IMAGE_FEATURES`.
	When creating a new project, the default is to provide you with an
	initial ``local.conf`` file that enables this feature using the
	:term:`EXTRA_IMAGE_FEATURES`
	variable with the line::

	EXTRA_IMAGE_FEATURES = "debug-tweaks"

	To disable that feature, simply comment out that line in your
	``local.conf`` file, or make sure :term:`IMAGE_FEATURES` does not contain
	"debug-tweaks" before producing your final image. Among other things,
	leaving this in place sets the root password as blank, which makes
	logging in for debugging or inspection easy during development but
	also means anyone can easily log in during production.

	- It is possible to set a root password for the image and also to set
	passwords for any extra users you might add (e.g. administrative or
	service type users). When you set up passwords for multiple images or
	users, you should not duplicate passwords.

	To set up passwords, use the :ref:`ref-classes-extrausers` class, which
	is the preferred method. For an example on how to set up both root and
	user passwords, see the ":ref:`ref-classes-extrausers`" section.

	.. note::

	When adding extra user accounts or setting a root password, be
	cautious about setting the same password on every device. If you
	do this, and the password you have set is exposed, then every
	device is now potentially compromised. If you need this access but
	want to ensure security, consider setting a different, random
	password for each device. Typically, you do this as a separate
	step after you deploy the image onto the device.

	- Consider enabling a Mandatory Access Control (MAC) framework such as
	SMACK or SELinux and tuning it appropriately for your device's usage.
	You can find more information in the
	:yocto_git:`meta-selinux </meta-selinux/>` layer.

	Tools for Hardening Your Image
	==============================

	The Yocto Project provides tools for making your image more secure. You
	can find these tools in the ``meta-security`` layer of the
	:yocto_git:`Yocto Project Source Repositories <>`.