systemd/man/systemd-pcrphase.service.xml

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<refentry id="systemd-pcrphase.service" conditional='HAVE_GNU_EFI'
          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-pcrphase</refname>
    <refpurpose>Measure boot phase into TPM2 PCR 11</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>/usr/lib/systemd/system-pcrphase</filename> <replaceable>STRING</replaceable></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>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 certain literal strings
    indicating various phases of the boot process into TPM2 PCR 11. During a regular boot process the
    following strings are extended into PCR 11:</para>

    <orderedlist>
      <listitem><para><literal>enter-initrd</literal> is extended into PCR 11 early when the initrd
      initializes, before activating system extension images for the initrd. It is supposed to act as 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 string is extended at start of
      <filename>systemd-pcrphase-initrd.service</filename>.)</para></listitem>

      <listitem><para><literal>leave-initrd</literal> is extended into PCR 11 when the initrd is about to
      transition into the host file system, i.e. when it achieved its purpose. It is supposed to act as
      barrier between kernel/initrd code and host OS code. (This string is extended at stop of
      <filename>systemd-pcrphase-initrd.service</filename>.)</para></listitem>

      <listitem><para><literal>sysinit</literal> is extended into PCR 11 when basic system initialization is
      complete (which includes local file systems have been mounted), and the system begins starting regular
      system services. (This string is extended at start of
      <filename>systemd-pcrphase-sysinit.service</filename>.)</para></listitem>

      <listitem><para><literal>ready</literal> is extended into PCR 11 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 is
      supposed to act as barrier between the time where unprivileged regular users are still prohibited to
      log in and where they are allowed to log in. (This string is extended at start of
      <filename>systemd-pcrphase.service</filename>.)</para></listitem>

      <listitem><para><literal>shutdown</literal> is extended into PCR 11 when system shutdown begins. It is
      supposed to act as barrier between the time the system is fully up and running and where it is about to
      shut down. (This string is extended at stop of
      <filename>systemd-pcrphase.service</filename>.)</para></listitem>

      <listitem><para><literal>final</literal> is extended into PCR 11 at the end of system shutdown. It is
      supposed to act 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 string is extended at
      stop of <filename>systemd-pcrphase-sysinit.service</filename>.)</para></listitem>
    </orderedlist>

    <para>During a regular system lifecycle, the strings <literal>enter-initrd</literal> →
    <literal>leave-initrd</literal> → <literal>sysinit</literal> → <literal>ready</literal> →
    <literal>shutdown</literal> → <literal>final</literal> are extended into PCR 11, one after the
    other.</para>

    <para>Specific phases of the boot process may be referenced via the series of strings measured, separated
    by colons (the "boot path"). For example, the boot 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 boot 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 boot 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>
  </refsect1>

  <refsect1>
    <title>Options</title>

    <para>The <filename>/usr/lib/systemd/system-pcrphase</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></listitem>
      </varlistentry>

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

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

    </variablelist>
  </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-measure</refentrytitle><manvolnum>1</manvolnum></citerefentry>
    </para>
  </refsect1>

</refentry>