dev-manual: Updated the "Making Images More Secure" section.

Fixes [YOCTO #5482]

I did some significant re-writing and re-organization of this
section.  It now includes a bit about securing an image in general,
provides general considerations, considerations specific to the
OpenEmbedded build system, pointers to some tools in meta-security
layer, and some other items.

(From yocto-docs rev: a900286992e781f451b3c180726965f5c7172bb9)

Signed-off-by: Scott Rifenbark <scott.m.rifenbark@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

1 files changed, 157 insertions, 23 deletions

diff --git a/documentation/dev-manual/dev-manual-common-tasks.xml b/documentation/dev-manual/dev-manual-common-tasks.xml
index aad8fb7787..d9fb9e2f4a 100644
--- a/documentation/dev-manual/dev-manual-common-tasks.xml
+++ b/documentation/dev-manual/dev-manual-common-tasks.xml
@@ -3841,32 +3841,166 @@
         <title>Making Images More Secure</title>
 
         <para>
-            The Yocto Project has security flags that you can enable that
-            help make your build output more secure.
-            The security flags are in the
-            <filename>meta/conf/distro/include/security_flags.inc</filename>
-            file in your
-            <link linkend='source-directory'>Source Directory</link>
-            (e.g. <filename>poky</filename>).
+            If 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.
+            The section does not offer a complete solution.
         </para>
 
-        <para>
-            These GCC/LD flags enable more secure code generation.
-            By including the <filename>security_flags.inc</filename>
-            file, you enable flags to the compiler and linker that cause
-            them to generate more secure code.
-            <note>
-                These flags are enabled by default in the
-                <filename>poky-lsb</filename> distribution.
-            </note>
-            Use the following line in your
-            <filename>local.conf</filename> file
-            to enable the security compiler and
-            linker flags to your build:
-            <literallayout class='monospaced'>
+        <section id='general-considerations'>
+            <title>General Considerations</title>
+
+            <para>
+                General considerations exist that help you create more
+                secure images.
+                You should consider the following suggestions to help
+                make your device more secure:
+                <itemizedlist>
+                    <listitem><para>
+                        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.
+                    </para></listitem>
+                    <listitem><para>
+                        Pay particular attention to to the security for
+                        any web-based administration interface.
+                        </para>
+                        <para>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.</para>
+                        <para>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.
+                    </para></listitem>
+                    <listitem><para>
+                        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.
+                    </para></listitem>
+                    <listitem><para>
+                        Ensure you remove or disable debugging functionality
+                        before producing the final image.
+                    </para></listitem>
+                    <listitem><para>
+                        Ensure you have no network services listening that
+                        are not needed.
+                    </para></listitem>
+                    <listitem><para>
+                        Remove any software from the image that is not needed.
+                    </para></listitem>
+                    <listitem><para>
+                        Enable hardware support for secure boot functionality
+                        when your device supports this functionality.
+                    </para></listitem>
+                </itemizedlist>
+            </para>
+        </section>
+
+        <section id='security-flags'>
+            <title>Security Flags</title>
+
+            <para>
+                The Yocto Project has security flags that you can enable that
+                help make your build output more secure.
+                The security flags are in the
+                <filename>meta/conf/distro/include/security_flags.inc</filename>
+                file in your
+                <link linkend='source-directory'>Source Directory</link>
+                (e.g. <filename>poky</filename>).
+                <note>
+                    Depending on the recipe, certain security flags are enabled
+                    and disabled by default.
+                </note>
+            </para>
+
+            <para>
+                The GCC/LD flags in <filename>security_flags.inc</filename>
+                enable more secure code generation.
+                By including the <filename>security_flags.inc</filename>
+                file, you enable flags to the compiler and linker that cause
+                them to generate more secure code.
+                <note>
+                    The GCC/LD flags are enabled by default in the
+                    <filename>poky-lsb</filename> distribution.
+                </note>
+                Use the following line in your
+                <filename>local.conf</filename> file
+                to enable the security compiler and
+                linker flags to your build:
+                <literallayout class='monospaced'>
      require conf/distro/include/security_flags.inc
-            </literallayout>
-        </para>
+                </literallayout>
+            </para>
+        </section>
+
+        <section id='considerations-specific-to-the-openembedded-build-system'>
+            <title>Considerations Specific to the OpenEmbedded Build System</title>
+
+            <para>
+                You can take some steps that are specific to the
+                OpenEmbedded build system to make your images more secure:
+                <itemizedlist>
+                    <listitem><para>
+                        Ensure "debug-tweaks" is not listed with
+                        <ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_FEATURES'><filename>IMAGE_FEATURES</filename></ulink>.
+                        The default is to enable "debug-tweaks" by adding it
+                        to
+                        <ulink url='&YOCTO_DOCS_REF_URL;#var-EXTRA_IMAGE_FEATURES'><filename>EXTRA_IMAGE_FEATURES</filename></ulink>
+                        in <filename>local.conf</filename>.
+                        However, you should comment out the variable or be
+                        sure that it does not have "debug-tweaks" before
+                        producing your final image.
+                        Among other things, leaving this in place sets the
+                        root password as blank.
+                    </para></listitem>
+                    <listitem><para>
+                        It is possible to set a root password or to add
+                        some additional user account for later administrative
+                        or service access using the
+                        <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-extrausers'><filename>extrausers</filename></ulink>
+                        class or the
+                        <ulink url='&YOCTO_DOCS_REF_URL;#var-ROOTFS_POSTPROCESS_COMMAND'><filename>ROOTFS_POSTPROCESS_COMMAND</filename></ulink>
+                        variable.
+                        If you do this, be cautious about setting
+                        the same password for every device.
+                        If you want the device to remain secure
+                        from unauthorized access, and the password set on
+                        all devices becomes compromised, then every device
+                        becomes compromised.
+                        If you need this access but want to ensure security,
+                        consider setting a different, random password for each
+                        device.
+                    </para></listitem>
+                </itemizedlist>
+            </para>
+        </section>
+
+        <section id='tools-for-hardening-your-image'>
+            <title>Tools for Hardening Your Image</title>
+
+            <para>
+                The Yocto Project provides tools for making your image
+                more secure.
+                You can find these tools in the
+                <filename>meta-security</filename> layer of the
+                <ulink url='&YOCTO_GIT_URL;/cgit/cgit.cgi'>Yocto Project Source Repositories</ulink>.
+            </para>
+        </section>
     </section>
 
     <section id='creating-your-own-distribution'>