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285 lines
15 KiB
XML
285 lines
15 KiB
XML
<?xml version="1.0"?>
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<!--*-nxml-*-->
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
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<refentry id="systemd-measure" xmlns:xi="http://www.w3.org/2001/XInclude" conditional='HAVE_GNU_EFI'>
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<refentryinfo>
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<title>systemd-measure</title>
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<productname>systemd</productname>
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</refentryinfo>
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<refmeta>
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<refentrytitle>systemd-measure</refentrytitle>
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<manvolnum>1</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>systemd-measure</refname>
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<refpurpose>Pre-calculate and sign expected TPM2 PCR values for booted unified kernel images</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<cmdsynopsis>
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<command>/usr/lib/systemd/systemd-measure <arg choice="opt" rep="repeat">OPTIONS</arg></command>
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</cmdsynopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para>Note: this command is experimental for now. While it is likely to become a regular component of
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systemd, it might still change in behaviour and interface.</para>
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<para><command>systemd-measure</command> is a tool that may be used to pre-calculate and sign the
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expected TPM2 PCR 11 values that should be seen when a unified Linux kernel image based on
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<citerefentry><refentrytitle>systemd-stub</refentrytitle><manvolnum>7</manvolnum></citerefentry> is
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booted up. It accepts paths to the ELF kernel image file, initrd image file, devicetree file, kernel
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command line file,
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<citerefentry><refentrytitle>os-release</refentrytitle><manvolnum>5</manvolnum></citerefentry> file, boot
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splash file, and TPM2 PCR PEM public key file that make up the unified kernel image, and determines the
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PCR values expected to be in place after booting the image. Calculation starts with a zero-initialized
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PCR 11, and is executed in a fashion compatible with what <filename>systemd-stub</filename> does at
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boot. The result may optionally be signed cryptographically, to allow TPM2 policies that can only be
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unlocked if a certain set of kernels is booted, for which such a PCR signature can be provided.</para>
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</refsect1>
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<refsect1>
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<title>Commands</title>
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<para>The following commands are understood:</para>
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<variablelist>
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<varlistentry>
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<term><command>status</command></term>
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<listitem><para>This is the default command if none is specified. This queries the local system's
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TPM2 PCR 11+12+13 values and displays them. The data is written in a similar format as the
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<command>calculate</command> command below, and may be used to quickly compare expectation with
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reality.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><command>calculate</command></term>
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<listitem><para>Pre-calculate the expected values seen in PCR register 11 after boot-up of a unified
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kernel image consisting of the components specified with <option>--linux=</option>,
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<option>--osrel=</option>, <option>--cmdline=</option>, <option>--initrd=</option>,
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<option>--splash=</option>, <option>--dtb=</option>, <option>--pcrpkey=</option> see below. Only
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<option>--linux=</option> is mandatory. (Alternatively, specify <option>--current</option> to use the
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current values of PCR register 11 instead.)</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><command>sign</command></term>
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<listitem><para>As with the <command>calculate</command> command, pre-calculate the expected value
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seen in TPM2 PCR register 11 after boot-up of a unified kernel image. Then, cryptographically sign
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the resulting values with the private/public key pair (RSA) configured via
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<option>--private-key=</option> and <option>--public-key=</option>. This will write a JSON object to
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standard output that contains signatures for all specified PCR banks (see
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<option>--pcr-bank=</option>) below, which may be used to unlock encrypted credentials (see
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<citerefentry><refentrytitle>systemd-creds</refentrytitle><manvolnum>1</manvolnum></citerefentry>) or
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LUKS volumes (see
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<citerefentry><refentrytitle>systemd-cryptsetup@.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>). This
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allows binding secrets to a set of kernels for which such PCR 11 signatures can be provided.</para>
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<para>Note that a TPM2 device must be available for this signing to take place, even though the
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result is not tied to any TPM2 device or its state.</para></listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1>
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<title>Options</title>
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<para>The following options are understood:</para>
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<variablelist>
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<varlistentry>
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<term><option>--linux=PATH</option></term>
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<term><option>--osrel=PATH</option></term>
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<term><option>--cmdline=PATH</option></term>
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<term><option>--initrd=PATH</option></term>
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<term><option>--splash=PATH</option></term>
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<term><option>--dtb=PATH</option></term>
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<term><option>--pcrpkey=PATH</option></term>
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<listitem><para>When used with the <command>calculate</command> or <command>sign</command> verb,
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configures the files to read the unified kernel image components from. Each option corresponds with
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the equally named section in the unified kernel PE file. The <option>--linux=</option> switch expects
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the path to the ELF kernel file that the unified PE kernel will wrap. All switches except
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<option>--linux=</option> are optional. Each option may be used at most once.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><option>--current</option></term>
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<listitem><para>When used with the <command>calculate</command> or <command>sign</command> verb,
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takes the PCR 11 values currently in effect for the system (which should typically reflect the hashes
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of the currently booted kernel). This can be used in place of <option>--linux=</option> and the other
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switches listed above.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><option>--bank=DIGEST</option></term>
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<listitem><para>Controls the PCR banks to pre-calculate the PCR values for – in case
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<command>calculate</command> or <command>sign</command> is invoked –, or the banks to show in the
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<command>status</command> output. May be used more then once to specify multiple banks. If not
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specified, defaults to the four banks <literal>sha1</literal>, <literal>sha256</literal>,
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<literal>sha384</literal>, <literal>sha512</literal>.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><option>--private-key=PATH</option></term>
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<term><option>--public-key=PATH</option></term>
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<listitem><para>These switches take paths to a pair of PEM encoded RSA key files, for use with
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the <command>sign</command> command.</para>
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<para>Note the difference between the <option>--pcrpkey=</option> and <option>--public-key=</option>
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switches. The former selects the data to include in the <literal>.pcrpkey</literal> PE section of the
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unified kernel image, the latter picks the public key of the key pair used to sign the resulting PCR
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11 values. The former is the key that the booted system will likely use to lock disk and credential
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encryption to, the latter is the key used for unlocking such resources again. Hence, typically the
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same PEM key should be supplied in both cases.</para>
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<para>If the <option>--public-key=</option> is not specified but <option>--private-key=</option> is
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specified the public key is automatically derived from the private key.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><option>--tpm2-device=</option><replaceable>PATH</replaceable></term>
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<listitem><para>Controls which TPM2 device to use. Expects a device node path referring to the TPM2
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chip (e.g. <filename>/dev/tpmrm0</filename>). Alternatively the special value <literal>auto</literal>
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may be specified, in order to automatically determine the device node of a suitable TPM2 device (of
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which there must be exactly one). The special value <literal>list</literal> may be used to enumerate
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all suitable TPM2 devices currently discovered.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><option>--phase=</option><replaceable>PHASE</replaceable></term>
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<listitem><para>Controls which boot phases to calculate expected PCR 11 values for. This takes a
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series of colon-separated strings that encode boot "paths" for entering a specific phase of the boot
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process. Each of the specified strings is measured by the
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<filename>systemd-pcrphase-initrd.service</filename> and
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<citerefentry><refentrytitle>systemd-pcrphase.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
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into PCR 11 during different milestones of the boot process. This switch may be specified multiple
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times to calculate PCR values for multiple boot phases at once. If not used defaults to
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<literal>enter-initrd</literal>, <literal>enter-initrd:leave-initrd</literal>,
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<literal>enter-initrd:leave-initrd:sysinit</literal>,
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<literal>enter-initrd:leave-initrd:sysinit:ready</literal>, i.e. calculates expected PCR values for
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the boot phase in the initrd, during early boot, during later boot, and during system runtime, but
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excluding the phases before the initrd or when shutting down. This setting is honoured both by
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<command>calculate</command> and <command>sign</command>. When used with the latter it's particularly
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useful for generating PCR signatures that can only be used for unlocking resources during specific
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parts of the boot process.</para>
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<para>For further details about PCR boot phases, see
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<citerefentry><refentrytitle>systemd-pcrphase.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para></listitem>
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</varlistentry>
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<xi:include href="standard-options.xml" xpointer="json" />
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<xi:include href="standard-options.xml" xpointer="no-pager" />
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<xi:include href="standard-options.xml" xpointer="help" />
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<xi:include href="standard-options.xml" xpointer="version" />
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</variablelist>
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</refsect1>
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<refsect1>
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<title>Examples</title>
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<example>
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<title>Generate a unified kernel image, and calculate the expected TPM PCR 11 value</title>
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<programlisting># objcopy \
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--add-section .linux=vmlinux --change-section-vma .linux=0x2000000 \
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--add-section .osrel=os-release.txt --change-section-vma .osrel=0x20000 \
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--add-section .cmdline=cmdline.txt --change-section-vma .cmdline=0x30000 \
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--add-section .initrd=initrd.cpio --change-section-vma .initrd=0x3000000 \
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--add-section .splash=splash.bmp --change-section-vma .splash=0x100000 \
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--add-section .dtb=devicetree.dtb --change-section-vma .dtb=0x40000 \
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/usr/lib/systemd/boot/efi/linuxx64.efi.stub \
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foo.efi
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# systemd-measure calculate \
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--linux=vmlinux \
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--osrel=os-release.txt \
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--cmdline=cmdline.txt \
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--initrd=initrd.cpio \
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--splash=splash.bmp \
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--dtb=devicetree.dtb
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11:sha1=d775a7b4482450ac77e03ee19bda90bd792d6ec7
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11:sha256=bc6170f9ce28eb051ab465cd62be8cf63985276766cf9faf527ffefb66f45651
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11:sha384=1cf67dff4757e61e5a73d2a21a6694d668629bbc3761747d493f7f49ad720be02fd07263e1f93061243aec599d1ee4b4
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11:sha512=8e79acd3ddbbc8282e98091849c3530f996303c8ac8e87a3b2378b71c8b3a6e86d5c4f41ecea9e1517090c3e8ec0c714821032038f525f744960bcd082d937da
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</programlisting>
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</example>
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<example>
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<title>Generate a private/public key pair, and a unified kernel image, and a TPM PCR 11 signature for
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it, and embed the signature and the public key in the image</title>
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<programlisting># openssl genpkey -algorithm RSA -pkeyopt rsa_keygen_bits:2048 -out tpm2-pcr-private.pem
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# openssl rsa -pubout -in tpm2-pcr-private.pem -out tpm2-pcr-public.pem
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# systemd-measure sign \
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--linux=vmlinux \
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--osrel=os-release.txt \
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--cmdline=cmdline.txt \
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--initrd=initrd.cpio \
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--splash=splash.bmp \
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--dtb=devicetree.dtb \
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--pcrpkey=tpm2-pcr-public.pem \
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--bank=sha1 \
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--bank=sha256 \
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--private-key=tpm2-pcr-private.pem \
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--public-key=tpm2-pcr-public.pem > tpm2-pcr-signature.json
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# objcopy \
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--add-section .linux=vmlinux --change-section-vma .linux=0x2000000 \
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--add-section .osrel=os-release.txt --change-section-vma .osrel=0x20000 \
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--add-section .cmdline=cmdline.txt --change-section-vma .cmdline=0x30000 \
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--add-section .initrd=initrd.cpio --change-section-vma .initrd=0x3000000 \
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--add-section .splash=splash.bmp --change-section-vma .splash=0x100000 \
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--add-section .dtb=devicetree.dtb --change-section-vma .dtb=0x40000 \
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--add-section .pcrsig=tpm2-pcr-signature.json --change-section-vma .splash=0x80000 \
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--add-section .pcrpkey=tpm2-pcr-public.pem --change-section-vma .splash=0x90000 \
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/usr/lib/systemd/boot/efi/linuxx64.efi.stub \
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foo.efi</programlisting>
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<para>Later on, enroll the signed PCR policy on a LUKS volume:</para>
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<programlisting># systemd-cryptenroll --tpm2-device=auto --tpm2-public-key=tpm2-pcr-public.pem --tpm2-signature=tpm2-pcr-signature.json /dev/sda5</programlisting>
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<para>And then unlock the device with the signature:</para>
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<programlisting># /usr/lib/systemd/systemd-cryptsetup attach myvolume /dev/sda5 - tpm2-device=auto,tpm2-signature=/path/to/tpm2-pcr-signature.json</programlisting>
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<para>Note that when the generated unified kernel image <filename>foo.efi</filename> is booted the
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signature and public key files will be placed at locations <command>systemd-cryptenroll</command> and
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<command>systemd-cryptsetup</command> will look for anyway, and thus these paths do not actually need to
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be specified.</para>
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</example>
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</refsect1>
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<refsect1>
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<title>Exit status</title>
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<para>On success, 0 is returned, a non-zero failure code otherwise.</para>
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</refsect1>
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<refsect1>
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<title>See Also</title>
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<para>
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<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemd-stub</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
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<citerefentry project='man-pages'><refentrytitle>objcopy</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemd-creds</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemd-cryptsetup@.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemd-pcrphase.service</refentrytitle><manvolnum>1</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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