systemd/man/systemd-pcrphase.service.xml

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<refentry id="systemd-pcrphase.service" conditional='ENABLE_BOOTLOADER HAVE_OPENSSL HAVE_TPM2'
          xmlns:xi="http://www.w3.org/2001/XInclude">

  <refentryinfo>
    <title>systemd-pcrphase.service</title>
    <productname>systemd</productname>
  </refentryinfo>

  <refmeta>
    <refentrytitle>systemd-pcrphase.service</refentrytitle>
    <manvolnum>8</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>systemd-pcrphase.service</refname>
    <refname>systemd-pcrphase-sysinit.service</refname>
    <refname>systemd-pcrphase-initrd.service</refname>
    <refname>systemd-pcrmachine.service</refname>
    <refname>systemd-pcrfs-root.service</refname>
    <refname>systemd-pcrfs@.service</refname>
    <refname>systemd-pcrextend</refname>
    <refpurpose>Measure boot phase into TPM2 PCR 11, machine ID and file system identity into PCR 15</refpurpose>
  </refnamediv>

  <refsynopsisdiv>
    <para><filename>systemd-pcrphase.service</filename></para>
    <para><filename>systemd-pcrphase-sysinit.service</filename></para>
    <para><filename>systemd-pcrphase-initrd.service</filename></para>
    <para><filename>systemd-pcrmachine.service</filename></para>
    <para><filename>systemd-pcrfs-root.service</filename></para>
    <para><filename>systemd-pcrfs@.service</filename></para>
    <para><filename>/usr/lib/systemd/systemd-pcrextend</filename> <optional><replaceable>STRING</replaceable></optional></para>
  </refsynopsisdiv>

  <refsect1>
    <title>Description</title>

    <para><filename>systemd-pcrphase.service</filename>,
    <filename>systemd-pcrphase-sysinit.service</filename>, and
    <filename>systemd-pcrphase-initrd.service</filename> are system services that measure specific strings
    into TPM2 PCR 11 during boot at various milestones of the boot process.</para>

    <para><filename>systemd-pcrmachine.service</filename> is a system service that measures the machine ID
    (see <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>) into
    PCR 15.</para>

    <para><filename>systemd-pcrfs-root.service</filename> and <filename>systemd-pcrfs@.service</filename> are
    services that measure file system identity information (i.e. mount point, file system type, label and
    UUID, partition label and UUID) into PCR 15. <filename>systemd-pcrfs-root.service</filename> does so for
    the root file system, <filename>systemd-pcrfs@.service</filename> is a template unit that measures the
    file system indicated by its instance identifier instead.</para>

    <para>These services require
    <citerefentry><refentrytitle>systemd-stub</refentrytitle><manvolnum>7</manvolnum></citerefentry> to be
    used in a unified kernel image (UKI). They execute no operation when the stub has not been used to invoke
    the kernel. The stub will measure the invoked kernel and associated vendor resources into PCR 11 before
    handing control to it; once userspace is invoked these services then will extend TPM2 PCR 11 with certain
    literal strings indicating phases of the boot process. During a regular boot process PCR 11 is extended
    with the following strings:</para>

    <orderedlist>
      <listitem><para><literal>enter-initrd</literal> — early when the initrd initializes, before activating
      system extension images for the initrd. It acts as a barrier between the time where the kernel
      initializes and where the initrd starts operating and enables system extension images, i.e. code
      shipped outside of the UKI. (This extension happens when the
      <citerefentry><refentrytitle>systemd-pcrphase-initrd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
      service is started.)</para></listitem>

      <listitem><para><literal>leave-initrd</literal> — when the initrd is about to transition into the host
      file system. It acts as barrier between initrd code and host OS code. (This extension happens when the
      <filename>systemd-pcrphase-initrd.service</filename> service is stopped.)</para></listitem>

      <listitem><para><literal>sysinit</literal> — when basic system initialization is complete (which
      includes local file systems having been mounted), and the system begins starting regular system
      services. (This extension happens when the
      <citerefentry><refentrytitle>systemd-pcrphase-sysinit.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
      service is started.)</para></listitem>

      <listitem><para><literal>ready</literal> — during later boot-up, after remote file systems have been
      activated (i.e. after <filename>remote-fs.target</filename>), but before users are permitted to log in
      (i.e. before <filename>systemd-user-sessions.service</filename>). It acts as barrier between the time
      where unprivileged regular users are still prohibited to log in and where they are allowed to log in.
      (This extension happens when the <filename>systemd-pcrphase.service</filename> service is started.)
      </para></listitem>

      <listitem><para><literal>shutdown</literal> — when the system shutdown begins. It acts as barrier
      between the time the system is fully up and running and where it is about to shut down. (This extension
      happens when the <filename>systemd-pcrphase.service</filename> service is stopped.)</para></listitem>

      <listitem><para><literal>final</literal> — at the end of system shutdown. It acts as barrier between
      the time the service manager still runs and when it transitions into the final shutdown phase where
      service management is not available anymore. (This extension happens when the
      <citerefentry><refentrytitle>systemd-pcrphase-sysinit.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
      service is stopped.)</para></listitem>
    </orderedlist>

    <para>During a regular system lifecycle, PCR 11 is extended with the strings
    <literal>enter-initrd</literal>, <literal>leave-initrd</literal>, <literal>sysinit</literal>,
    <literal>ready</literal>, <literal>shutdown</literal>, and <literal>final</literal>.</para>

    <para>Specific phases of the boot process may be referenced via the series of strings measured, separated
    by colons (the "phase path"). For example, the phase path for the regular system runtime is
    <literal>enter-initrd:leave-initrd:sysinit:ready</literal>, while the one for the initrd is just
    <literal>enter-initrd</literal>. The phase path for the boot phase before the initrd is an empty string;
    because that's hard to pass around a single colon (<literal>:</literal>) may be used instead. Note that
    the aforementioned six strings are just the default strings and individual systems might measure other
    strings at other times, and thus implement different and more fine-grained boot phases to bind policy
    to.</para>

    <para>By binding policy of TPM2 objects to a specific phase path it is possible to restrict access to
    them to specific phases of the boot process, for example making it impossible to access the root file
    system's encryption key after the system transitioned from the initrd into the host root file system.
    </para>

    <para>Use
    <citerefentry><refentrytitle>systemd-measure</refentrytitle><manvolnum>1</manvolnum></citerefentry> to
    pre-calculate expected PCR 11 values for specific boot phases (via the <option>--phase=</option> switch).
    </para>

    <para><filename>systemd-pcrfs-root.service</filename> and <filename>systemd-pcrfs@.service</filename> are
    automatically pulled into the initial transaction by
    <citerefentry><refentrytitle>systemd-gpt-auto-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>
    for the root and <filename>/var/</filename> file
    systems. <citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>
    will do this for all mounts with the <option>x-systemd.pcrfs</option> mount option in
    <filename>/etc/fstab</filename>.</para>
  </refsect1>

  <refsect1>
    <title>Options</title>

    <para>The <filename>/usr/lib/systemd/system-pcrextend</filename> executable may also be invoked from the
    command line, where it expects the word to extend into PCR 11, as well as the following switches:</para>

    <variablelist>
      <varlistentry>
        <term><option>--bank=</option></term>

        <listitem><para>Takes the PCR banks to extend the specified word into. If not specified the tool
        automatically determines all enabled PCR banks and measures the word into all of
        them.</para>

        <xi:include href="version-info.xml" xpointer="v252"/></listitem>
      </varlistentry>

      <varlistentry>
        <term><option>--pcr=</option></term>

        <listitem><para>Takes the index of the PCR to extend. If <option>--machine-id</option> or
        <option>--file-system=</option> are specified defaults to 15, otherwise defaults to 11.</para>

        <xi:include href="version-info.xml" xpointer="v255"/></listitem>
      </varlistentry>

      <varlistentry>
        <term><option>--tpm2-device=<replaceable>PATH</replaceable></option></term>

        <listitem><para>Controls which TPM2 device to use. Expects a device node path referring to the TPM2
        chip (e.g. <filename>/dev/tpmrm0</filename>). Alternatively the special value <literal>auto</literal>
        may be specified, in order to automatically determine the device node of a suitable TPM2 device (of
        which there must be exactly one). The special value <literal>list</literal> may be used to enumerate
        all suitable TPM2 devices currently discovered.</para>

        <xi:include href="version-info.xml" xpointer="v252"/></listitem>
      </varlistentry>

      <varlistentry>
        <term><option>--graceful</option></term>

        <listitem><para>If no TPM2 firmware, kernel subsystem, kernel driver or device support is found, exit
        with exit status 0 (i.e. indicate success). If this is not specified any attempt to measure without a
        TPM2 device will cause the invocation to fail.</para>

        <xi:include href="version-info.xml" xpointer="v253"/></listitem>
      </varlistentry>

      <varlistentry>
        <term><option>--machine-id</option></term>

        <listitem><para>Instead of measuring a word specified on the command line into PCR 11, measure the
        host's machine ID into PCR 15.</para>

        <xi:include href="version-info.xml" xpointer="v253"/></listitem>
      </varlistentry>

      <varlistentry>
        <term><option>--file-system=</option></term>

        <listitem><para>Instead of measuring a word specified on the command line into PCR 11, measure
        identity information of the specified file system into PCR 15. The parameter must be the path to the
        established mount point of the file system to measure.</para>

        <xi:include href="version-info.xml" xpointer="v253"/></listitem>
      </varlistentry>

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

    </variablelist>
  </refsect1>

  <refsect1>
    <title>Files</title>

    <variablelist>
      <varlistentry>
        <term><filename>/run/log/systemd/tpm2-measure.log</filename></term>

        <listitem><para>Measurements are logged into an event log file maintained in
        <filename>/run/log/systemd/tpm2-measure.log</filename>, which contains a <ulink
        url="https://www.rfc-editor.org/rfc/rfc7464.html">JSON-SEQ</ulink> series of objects that follow the
        general structure of the <ulink
        url="https://trustedcomputinggroup.org/resource/canonical-event-log-format/">TCG Canonical Event Log
        Format (CEL-JSON)</ulink> event objects (but lack the <literal>recnum</literal>
        field).</para>

        <para>A <constant>LOCK_EX</constant> BSD file lock (<citerefentry
        project='man-pages'><refentrytitle>flock</refentrytitle><manvolnum>2</manvolnum></citerefentry>) on
        the log file is acquired while the measurement is made and the file is updated. Thus, applications
        that intend to acquire a consistent quote from the TPM with the associated snapshot of the event log
        should acquire a <constant>LOCK_SH</constant> lock while doing so.</para>

        <xi:include href="version-info.xml" xpointer="v252"/></listitem>
      </varlistentry>
    </variablelist>
  </refsect1>

  <refsect1>
    <title>See Also</title>
    <para><simplelist type="inline">
      <member><citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
      <member><citerefentry><refentrytitle>systemd-stub</refentrytitle><manvolnum>7</manvolnum></citerefentry></member>
      <member><citerefentry><refentrytitle>systemd-measure</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
      <member><citerefentry><refentrytitle>systemd-gpt-auto-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
      <member><citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
      <member><ulink url="https://systemd.io/TPM2_PCR_MEASUREMENTS">TPM2 PCR Measurements Made by systemd</ulink></member>
    </simplelist></para>
  </refsect1>

</refentry>