systemd/man/ukify.xml

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<refentry id="ukify" xmlns:xi="http://www.w3.org/2001/XInclude" conditional='ENABLE_UKIFY'>

  <refentryinfo>
    <title>ukify</title>
    <productname>systemd</productname>
  </refentryinfo>

  <refmeta>
    <refentrytitle>ukify</refentrytitle>
    <manvolnum>1</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>ukify</refname>
    <refpurpose>Combine kernel and initrd into a signed Unified Kernel Image</refpurpose>
  </refnamediv>

  <refsynopsisdiv>
    <cmdsynopsis>
      <command>/usr/lib/systemd/ukify</command>
      <arg choice="plain"><replaceable>LINUX</replaceable></arg>
      <arg choice="plain" rep="repeat"><replaceable>INITRD</replaceable></arg>
      <arg choice="opt" rep="repeat">OPTIONS</arg>
    </cmdsynopsis>
  </refsynopsisdiv>

  <refsect1>
    <title>Description</title>

    <para>Note: this command is experimental for now. While it is intended to become a regular component of
    systemd, it might still change in behaviour and interface.</para>

    <para><command>ukify</command> is a tool that combines a kernel and an initrd with
    a UEFI boot stub to create a
    <ulink url="https://uapi-group.org/specifications/specs/unified_kernel_image/">Unified Kernel Image (UKI)</ulink>
    — a PE binary that can be executed by the firmware to start the embedded linux kernel.
    See <citerefentry><refentrytitle>systemd-stub</refentrytitle><manvolnum>7</manvolnum></citerefentry>
    for details about the stub.</para>

    <para>Additional sections will be inserted into the UKI, either automatically or only if a specific
    option is provided. See the discussions of
    <option>--cmdline=</option>,
    <option>--os-release=</option>,
    <option>--devicetree=</option>,
    <option>--splash=</option>,
    <option>--pcrpkey=</option>,
    <option>--uname=</option>,
    and <option>--section=</option>
    below.</para>

    <para>If PCR signing keys are provided via the <option>--pcr-public-key=</option> and
    <option>--pcr-private-key=</option> options, PCR values that will be seen after booting with the given
    kernel, initrd, and other sections, will be calculated, signed, and embedded in the UKI.
    <citerefentry><refentrytitle>systemd-measure</refentrytitle><manvolnum>1</manvolnum></citerefentry> is
    used to perform this calculation and signing.</para>

    <para>The calculation of PCR values is done for specific boot phase paths. Those can be specified with
    <option>--phases=</option> option. If not specified, the default provided by
    <command>systemd-measure</command> is used. It is also possible to specify the
    <option>--pcr-private-key=</option>, <option>--pcr-public-key=</option>, and <option>--phases=</option>
    arguments more than once. Signatures will be then performed with each of the specified keys. When both
    <option>--phases=</option> and <option>--pcr-private-key=</option> are used, they must be specified the
    same number of times, and then the n-th boot phase path set will be signed by the n-th key. This can be
    used to build different trust policies for different phases of the boot.</para>

    <para>If a SecureBoot signing key is provided via the <option>--secureboot-private-key=</option> option,
    the resulting PE binary will be signed as a whole, allowing the resulting UKI to be trusted by
    SecureBoot. Also see the discussion of automatic enrollment in
    <citerefentry><refentrytitle>systemd-boot</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
    </para>
  </refsect1>

  <refsect1>
    <title>Options</title>

    <para>Note that the <replaceable>LINUX</replaceable> positional argument is mandatory. The
    <replaceable>INITRD</replaceable> positional arguments are optional. If more than one is specified, they
    will all be combined into a single PE section. This is useful to for example prepend microcode before the
    actual initrd.</para>

    <para>The following options are understood:</para>

    <variablelist>
      <varlistentry>
        <term><option>--cmdline=<replaceable>TEXT</replaceable>|<replaceable>@PATH</replaceable></option></term>

        <listitem><para>Specify the kernel command line (the <literal>.cmdline</literal> section). The
        argument may be a literal string, or <literal>@</literal> followed by a path name. If not specified,
        no command line will be embedded.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><option>--os-release=<replaceable>TEXT</replaceable>|<replaceable>@PATH</replaceable></option></term>

        <listitem><para>Specify the os-release description (the <literal>.osrel</literal> section). The
        argument may be a literal string, or <literal>@</literal> followed by a path name. If not specified,
        the <citerefentry><refentrytitle>os-release</refentrytitle><manvolnum>5</manvolnum></citerefentry>
        file will be picked up from the host system.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><option>--devicetree=<replaceable>PATH</replaceable></option></term>

        <listitem><para>Specify the devicetree description (the <literal>.dtb</literal> section). The
        argument is a path to a compiled binary DeviceTree file. If not specified, the section will not be
        present.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><option>--splash=<replaceable>PATH</replaceable></option></term>

        <listitem><para>Specify a picture to display during boot (the <literal>.splash</literal> section).
        The argument is a path to a BMP file. If not specified, the section will not be present.
        </para></listitem>
      </varlistentry>

      <varlistentry>
        <term><option>--pcrpkey=<replaceable>PATH</replaceable></option></term>

        <listitem><para>Specify a path to a public key to embed in the <literal>.pcrpkey</literal> section.
        If not specified, and there's exactly one <option>--pcr-public-key=</option> argument, that key will
        be used. Otherwise, the section will not be present.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><option>--uname=<replaceable>VERSION</replaceable></option></term>

        <listitem><para>Specify the kernel version (as in <command>uname -r</command>, the
        <literal>.uname</literal> section). If not specified, an attempt will be made to extract the version
        string from the kernel image. It is recommended to pass this explicitly if known, because the
        extraction is based on heuristics and not very reliable. If not specified and extraction fails, the
        section will not be present.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><option>--section=<replaceable>NAME</replaceable>:<replaceable>TEXT</replaceable>|<replaceable>@PATH</replaceable></option></term>

        <listitem><para>Specify an arbitrary additional section
        <literal><replaceable>NAME</replaceable></literal>. Note that the name is used as-is, and if the
        section name should start with a dot, it must be included in <replaceable>NAME</replaceable>. The
        argument may be a literal string, or <literal>@</literal> followed by a path name. This option may be
        specified more than once. Any sections specified in this fashion will be inserted (in order) before
        the <literal>.linux</literal> section which is always last.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><option>--pcr-private-key=<replaceable>PATH</replaceable></option></term>

        <listitem><para>Specify a private key to use for signing PCR policies. This option may be specified
        more than once, in which case multiple signatures will be made.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><option>--pcr-public-key=<replaceable>PATH</replaceable></option></term>

        <listitem><para>Specify a public key to use for signing PCR policies. This option may be specified
        more than once, similarly to the <option>--pcr-private-key=</option> option. If not present, the
        public keys will be extracted from the private keys. If present, the this option must be specified
        the same number of times as the <option>--pcr-private-key=</option> option.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><option>--phases=<replaceable>LIST</replaceable></option></term>

        <listitem><para>A comma or space-separated list of colon-separated phase paths to sign a policy for.
        If not present, the default of
        <citerefentry><refentrytitle>systemd-measure</refentrytitle><manvolnum>1</manvolnum></citerefentry>
        will be used. When this argument is present, it must appear the same number of times as the
        <option>--pcr-private-key=</option> option. Each set of boot phase paths will be signed with the
        corresponding private key.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><option>--pcr-banks=<replaceable>PATH</replaceable></option></term>

        <listitem><para>A comma or space-separated list of PCR banks to sign a policy for. If not present,
        all known banks will be used (<literal>sha1</literal>, <literal>sha256</literal>,
        <literal>sha384</literal>, <literal>sha512</literal>), which will fail if not supported by the
        system.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><option>--secureboot-private-key=<replaceable>SB_KEY</replaceable></option></term>

        <listitem><para>A path to a private key to use for signing of the resulting binary. If the
        <option>--signing-engine=</option> option is used, this may also be an engine-specific
        designation.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><option>--secureboot-certificate=<replaceable>SB_CERT</replaceable></option></term>

        <listitem><para>A path to a certificate to use for signing of the resulting binary. If the
        <option>--signing-engine=</option> option is used, this may also be an engine-specific
        designation.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><option>--signing-engine=<replaceable>ENGINE</replaceable></option></term>

        <listitem><para>An "engine" to for signing of the resulting binary. This option is currently passed
        verbatim to the <option>--engine=</option> option of
        <citerefentry project='archlinux'><refentrytitle>sbsign</refentrytitle><manvolnum>1</manvolnum></citerefentry>.
        </para></listitem>
      </varlistentry>

      <varlistentry>
        <term><option>--sign-kernel</option></term>
        <term><option>--no-sign-kernel</option></term>

        <listitem><para>Override the detection of whether to sign the Linux binary itself before it is
        embedded in the combined image. If not specified, it will be signed if a SecureBoot signing key is
        provided via the <option>--secureboot-private-key=</option> option and the binary has not already
        been signed. If <option>--sign-kernel</option> is specified, and the binary has already been signed,
        the signature will be appended anyway.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><option>--tools=<replaceable>DIRS</replaceable></option></term>

        <listitem><para>Specify one or more directories with helper tools. <command>ukify</command> will look
        for helper tools in those directories first, and if not found, try to load them from
        <varname>$PATH</varname> in the usual fashion.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><option>--measure</option></term>
        <term><option>--no-measure</option></term>

        <listitem><para>Enable or disable a call to <command>systmed-measure</command> to print
        pre-calculated PCR values. Defaults to false.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><option>--output=<replaceable>FILENAME</replaceable></option></term>

        <listitem><para>The output filename. If not specified, the name of the
        <replaceable>LINUX</replaceable> argument, with the suffix <literal>.unsigned.efi</literal> or
        <literal>.signed.efi</literal> will be used, depending on whether signing for SecureBoot was
        performed.</para></listitem>
      </varlistentry>

      <xi:include href="standard-options.xml" xpointer="help" />
      <xi:include href="standard-options.xml" xpointer="version" />
    </variablelist>
  </refsect1>

  <refsect1>
    <title>Examples</title>

    <example>
      <title>Minimal invocation</title>

      <programlisting>ukify \
      /lib/modules/6.0.9-300.fc37.x86_64/vmlinuz \
      /some/path/initramfs-6.0.9-300.fc37.x86_64.img \
      --cmdline='quiet rw'
      </programlisting>

      <para>This creates an unsigned UKI <filename>./vmlinuz.unsigned.efi</filename>.</para>
    </example>

    <example>
      <title>All the bells and whistles</title>

      <programlisting>/usr/lib/systemd/ukify \
      /lib/modules/6.0.9-300.fc37.x86_64/vmlinuz \
      early_cpio \
      /some/path/initramfs-6.0.9-300.fc37.x86_64.img \
      --pcr-private-key=pcr-private-initrd-key.pem \
      --pcr-public-key=pcr-public-initrd-key.pem \
      --phases='enter-initrd' \
      --pcr-private-key=pcr-private-system-key.pem \
      --pcr-public-key=pcr-public-system-key.pem \
      --phases='enter-initrd:leave-initrd enter-initrd:leave-initrd:sysinit \
                enter-initrd:leave-initrd:sysinit:ready' \
      --pcr-banks=sha384,sha512 \
      --secureboot-private-key=sb.key \
      --secureboot-certificate=sb.cert \
      --sign-kernel \
      --cmdline='quiet rw rhgb'
      </programlisting>

      <para>This creates a signed UKI <filename index='false'>./vmlinuz.signed.efi</filename>.
      The initrd section contains two concatenated parts, <filename index='false'>early_cpio</filename>
      and <filename index='false'>initramfs-6.0.9-300.fc37.x86_64.img</filename>.
      The policy embedded in the <literal>.pcrsig</literal> section will be signed for the initrd (the
      <constant>enter-initrd</constant> phase) with the key
      <filename index='false'>pcr-private-initrd-key.pem</filename>, and for the main system (phases
      <constant>leave-initrd</constant>, <constant>sysinit</constant>, <constant>ready</constant>) with the
      key <filename index='false'>pcr-private-system-key.pem</filename>. The Linux binary and the resulting
      combined image will be signed with the SecureBoot key <filename index='false'>sb.key</filename>.</para>
    </example>
  </refsect1>

  <refsect1>
    <title>See Also</title>
    <para>
      <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>systemd-stub</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>systemd-boot</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
      <citerefentry project='man-pages'><refentrytitle>objcopy</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>systemd-pcrphase.service</refentrytitle><manvolnum>1</manvolnum></citerefentry>
     </para>
  </refsect1>

</refentry>