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diff --git a/man/systemd-measure.xml b/man/systemd-measure.xml new file mode 100644 index 0000000..ff3abc4 --- /dev/null +++ b/man/systemd-measure.xml @@ -0,0 +1,388 @@ +<?xml version="1.0"?> +<!--*-nxml-*--> +<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" + "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> +<!-- SPDX-License-Identifier: LGPL-2.1-or-later --> +<refentry id="systemd-measure" xmlns:xi="http://www.w3.org/2001/XInclude" conditional='ENABLE_BOOTLOADER'> + + <refentryinfo> + <title>systemd-measure</title> + <productname>systemd</productname> + </refentryinfo> + + <refmeta> + <refentrytitle>systemd-measure</refentrytitle> + <manvolnum>1</manvolnum> + </refmeta> + + <refnamediv> + <refname>systemd-measure</refname> + <refpurpose>Pre-calculate and sign expected TPM2 PCR values for booted unified kernel images</refpurpose> + </refnamediv> + + <refsynopsisdiv> + <cmdsynopsis> + <command>/usr/lib/systemd/systemd-measure <arg choice="opt" rep="repeat">OPTIONS</arg></command> + </cmdsynopsis> + </refsynopsisdiv> + + <refsect1> + <title>Description</title> + + <para>Note: this command is experimental for now. While it is likely to become a regular component of + systemd, it might still change in behaviour and interface.</para> + + <para><command>systemd-measure</command> is a tool that may be used to pre-calculate and sign the + expected TPM2 PCR 11 values that should be seen when a Linux <ulink + url="https://uapi-group.org/specifications/specs/unified_kernel_image/">Unified Kernel Image + (UKI)</ulink> based on + <citerefentry><refentrytitle>systemd-stub</refentrytitle><manvolnum>7</manvolnum></citerefentry> is + booted up. It accepts paths to the ELF kernel image file, initrd image file, devicetree file, kernel + command line file, + <citerefentry><refentrytitle>os-release</refentrytitle><manvolnum>5</manvolnum></citerefentry> file, boot + splash file, and TPM2 PCR PEM public key file that make up the unified kernel image, and determines the + PCR values expected to be in place after booting the image. Calculation starts with a zero-initialized + PCR 11, and is executed in a fashion compatible with what <filename>systemd-stub</filename> does at boot. + The result may optionally be signed cryptographically, to allow TPM2 policies that can only be unlocked + if a certain set of kernels is booted, for which such a PCR signature can be provided.</para> + + <para>It usually doesn't make sense to call this tool directly when constructing a UKI. Instead, + <citerefentry><refentrytitle>ukify</refentrytitle><manvolnum>1</manvolnum></citerefentry> should be used; + it will invoke <command>systemd-measure</command> and take care of embedding the resulting measurements + into the UKI.</para> + </refsect1> + + <refsect1> + <title>Commands</title> + + <para>The following commands are understood:</para> + + <variablelist> + <varlistentry> + <term><command>status</command></term> + + <listitem><para>This is the default command if none is specified. This queries the local system's + TPM2 PCR 11+12+13 values and displays them. The data is written in a similar format as the + <command>calculate</command> command below, and may be used to quickly compare expectation with + reality.</para> + + <xi:include href="version-info.xml" xpointer="v252"/></listitem> + </varlistentry> + + <varlistentry> + <term><command>calculate</command></term> + + <listitem><para>Pre-calculate the expected values seen in PCR register 11 after boot-up of a unified + kernel image consisting of the components specified with <option>--linux=</option>, + <option>--osrel=</option>, <option>--cmdline=</option>, <option>--initrd=</option>, + <option>--splash=</option>, <option>--dtb=</option>, <option>--uname=</option>, + <option>--sbat=</option>, <option>--pcrpkey=</option> see below. Only <option>--linux=</option> is + mandatory. (Alternatively, specify <option>--current</option> to use the current values of PCR + register 11 instead.)</para> + + <xi:include href="version-info.xml" xpointer="v252"/> + </listitem> + </varlistentry> + + <varlistentry> + <term><command>sign</command></term> + + <listitem><para>As with the <command>calculate</command> command, pre-calculate the expected value + seen in TPM2 PCR register 11 after boot-up of a unified kernel image. Then, cryptographically sign + the resulting values with the private/public key pair (RSA) configured via + <option>--private-key=</option> and <option>--public-key=</option>. This will write a JSON object to + standard output that contains signatures for all specified PCR banks (see the + <option>--bank=</option> option below), which may be used to unlock encrypted credentials (see + <citerefentry><refentrytitle>systemd-creds</refentrytitle><manvolnum>1</manvolnum></citerefentry>) or + LUKS volumes (see + <citerefentry><refentrytitle>systemd-cryptsetup@.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>). + This allows binding secrets to a set of kernels for which such PCR 11 signatures can be + provided.</para> + + <para>Note that a TPM2 device must be available for this signing to take place, even though the + result is not tied to any TPM2 device or its state.</para> + + <xi:include href="version-info.xml" xpointer="v252"/></listitem> + </varlistentry> + </variablelist> + </refsect1> + + <refsect1> + <title>Options</title> + + <para>The following options are understood:</para> + + <variablelist> + <varlistentry> + <term><option>--linux=<replaceable>PATH</replaceable></option></term> + <term><option>--osrel=<replaceable>PATH</replaceable></option></term> + <term><option>--cmdline=<replaceable>PATH</replaceable></option></term> + <term><option>--initrd=<replaceable>PATH</replaceable></option></term> + <term><option>--splash=<replaceable>PATH</replaceable></option></term> + <term><option>--dtb=<replaceable>PATH</replaceable></option></term> + <term><option>--uname=<replaceable>PATH</replaceable></option></term> + <term><option>--sbat=<replaceable>PATH</replaceable></option></term> + <term><option>--pcrpkey=<replaceable>PATH</replaceable></option></term> + + <listitem><para>When used with the <command>calculate</command> or <command>sign</command> verb, + configures the files to read the unified kernel image components from. Each option corresponds with + the equally named section in the unified kernel PE file. The <option>--linux=</option> switch expects + the path to the ELF kernel file that the unified PE kernel will wrap. All switches except + <option>--linux=</option> are optional. Each option may be used at most once.</para> + + <xi:include href="version-info.xml" xpointer="v252"/></listitem> + </varlistentry> + + <varlistentry> + <term><option>--current</option></term> + <listitem><para>When used with the <command>calculate</command> or <command>sign</command> verb, + takes the PCR 11 values currently in effect for the system (which should typically reflect the hashes + of the currently booted kernel). This can be used in place of <option>--linux=</option> and the other + switches listed above.</para> + + <xi:include href="version-info.xml" xpointer="v252"/></listitem> + </varlistentry> + + <varlistentry> + <term><option>--bank=<replaceable>DIGEST</replaceable></option></term> + + <listitem><para>Controls the PCR banks to pre-calculate the PCR values for – in case + <command>calculate</command> or <command>sign</command> is invoked –, or the banks to show in the + <command>status</command> output. May be used more then once to specify multiple banks. If not + specified, defaults to the four banks <literal>sha1</literal>, <literal>sha256</literal>, + <literal>sha384</literal>, <literal>sha512</literal>.</para> + + <xi:include href="version-info.xml" xpointer="v252"/></listitem> + </varlistentry> + + <varlistentry> + <term><option>--private-key=<replaceable>PATH</replaceable></option></term> + <term><option>--public-key=<replaceable>PATH</replaceable></option></term> + + <listitem><para>These switches take paths to a pair of PEM encoded RSA key files, for use with + the <command>sign</command> command.</para> + + <para>Note the difference between the <option>--pcrpkey=</option> and <option>--public-key=</option> + switches. The former selects the data to include in the <literal>.pcrpkey</literal> PE section of the + unified kernel image, the latter picks the public key of the key pair used to sign the resulting PCR + 11 values. The former is the key that the booted system will likely use to lock disk and credential + encryption to, the latter is the key used for unlocking such resources again. Hence, typically the + same PEM key should be supplied in both cases.</para> + + <para>If the <option>--public-key=</option> is not specified but <option>--private-key=</option> is + specified the public key is automatically derived from the private key.</para> + + <xi:include href="version-info.xml" xpointer="v252"/></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> + + <xi:include href="version-info.xml" xpointer="v252"/></listitem> + </varlistentry> + + <varlistentry> + <term><option>--phase=</option><replaceable>PHASE</replaceable></term> + + <listitem><para>Controls which boot phases to calculate expected PCR 11 values for. This takes a + series of colon-separated strings that encode boot "paths" for entering a specific phase of the boot + process. Each of the specified strings is measured by the + <filename>systemd-pcrphase-initrd.service</filename>, + <filename>systemd-pcrphase-sysinit.service</filename>, and + <citerefentry><refentrytitle>systemd-pcrphase.service</refentrytitle><manvolnum>8</manvolnum></citerefentry> + into PCR 11 during different milestones of the boot process. This switch may be specified multiple + times to calculate PCR values for multiple boot phases at once. If not used defaults to + <literal>enter-initrd</literal>, <literal>enter-initrd:leave-initrd</literal>, + <literal>enter-initrd:leave-initrd:sysinit</literal>, + <literal>enter-initrd:leave-initrd:sysinit:ready</literal>, i.e. calculates expected PCR values for + the boot phase in the initrd, during early boot, during later boot, and during system runtime, but + excluding the phases before the initrd or when shutting down. This setting is honoured both by + <command>calculate</command> and <command>sign</command>. When used with the latter it's particularly + useful for generating PCR signatures that can only be used for unlocking resources during specific + parts of the boot process.</para> + + <para>For further details about PCR boot phases, see + <citerefentry><refentrytitle>systemd-pcrphase.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para> + + <xi:include href="version-info.xml" xpointer="v252"/></listitem> + </varlistentry> + + <varlistentry> + <term><option>--append=</option><replaceable>PATH</replaceable></term> + + <listitem><para>When generating a PCR JSON signature (via the <command>sign</command> command), + combine it with a previously generated PCR JSON signature, and output it as one. The specified path + must refer to a regular file that contains a valid JSON PCR signature object. The specified file is + not modified. It will be read first, then the newly generated signature appended to it, and the + resulting object is written to standard output. Use this to generate a single JSON object consisting + from signatures made with a number of signing keys (for example, to have one key per boot phase). The + command will suppress duplicates: if a specific signature is already included in a JSON signature + object it is not added a second time.</para> + + <xi:include href="version-info.xml" xpointer="v253"/></listitem> + </varlistentry> + + <xi:include href="standard-options.xml" xpointer="json" /> + <xi:include href="standard-options.xml" xpointer="no-pager" /> + <xi:include href="standard-options.xml" xpointer="help" /> + <xi:include href="standard-options.xml" xpointer="version" /> + </variablelist> + </refsect1> + + <refsect1> + <title>Examples</title> + + <example> + <title>Generate a unified kernel image, and calculate the expected TPM PCR 11 value</title> + + <programlisting>$ ukify --output=vmlinux.efi \ + --os-release=@os-release.txt \ + --cmdline=@cmdline.txt \ + --splash=splash.bmp \ + --devicetree=devicetree.dtb \ + --measure \ + vmlinux initrd.cpio +11:sha1=d775a7b4482450ac77e03ee19bda90bd792d6ec7 +11:sha256=bc6170f9ce28eb051ab465cd62be8cf63985276766cf9faf527ffefb66f45651 +11:sha384=1cf67dff4757e61e5...7f49ad720be02fd07263e1f93061243aec599d1ee4b4 +11:sha512=8e79acd3ddbbc8282...0c3e8ec0c714821032038f525f744960bcd082d937da +</programlisting> + + <para><citerefentry><refentrytitle>ukify</refentrytitle><manvolnum>1</manvolnum></citerefentry> + internally calls <command>systemd-measure</command>. The output with hashes is from + <command>systemd-measure</command>.</para> + </example> + + <example> + <title>Generate a private/public key pair, a unified kernel image, and a TPM PCR 11 signature for + it, and embed the signature and the public key in the image</title> + + <programlisting>$ openssl genpkey -algorithm RSA -pkeyopt rsa_keygen_bits:2048 -out tpm2-pcr-private.pem +..+.+++++++++......+.........+......+.......+....+.....+.+...+.......... +$ openssl rsa -pubout -in tpm2-pcr-private.pem -out tpm2-pcr-public.pem +# systemd-measure sign \ + --linux=vmlinux \ + --osrel=os-release.txt \ + --cmdline=cmdline.txt \ + --initrd=initrd.cpio \ + --splash=splash.bmp \ + --dtb=devicetree.dtb \ + --pcrpkey=tpm2-pcr-public.pem \ + --bank=sha1 \ + --bank=sha256 \ + --private-key=tpm2-pcr-private.pem \ + --public-key=tpm2-pcr-public.pem >tpm2-pcr-signature.json +# ukify --output=vmlinuz.efi \ + --os-release=@os-release.txt \ + --cmdline=@cmdline.txt \ + --splash=splash.bmp \ + --devicetree=devicetree.dtb \ + --pcr-private-key=tpm2-pcr-private.pem \ + --pcr-public-key=tpm2-pcr-public.pem \ + --pcr-banks=sha1,sha256 \ + vmlinux initrd.cpio</programlisting> + + <para>Later on, enroll the signed PCR policy on a LUKS volume:</para> + + <programlisting># systemd-cryptenroll --tpm2-device=auto \ + --tpm2-public-key=tpm2-pcr-public.pem \ + --tpm2-signature=tpm2-pcr-signature.json \ + /dev/sda5</programlisting> + + <para>And then unlock the device with the signature:</para> + + <programlisting># systemd-cryptsetup attach \ + volume5 /dev/sda5 - \ + tpm2-device=auto,tpm2-signature=/path/to/tpm2-pcr-signature.json</programlisting> + + <para>Note that when the generated unified kernel image <filename>vmlinux.efi</filename> is booted, the + signature and public key files will be placed at locations <command>systemd-cryptenroll</command> and + <command>systemd-cryptsetup</command> will look for anyway, and thus these paths do not actually need to + be specified.</para> + </example> + + <example> + <title>Introduce a second public key, signing the same kernel PCR measurements, but only for the initrd boot phase</title> + + <para>This example extends the previous one, but we now introduce a second signing key that is only + used to sign PCR policies restricted to the initrd boot phase. This can be used to lock down root + volumes in a way that they can only be unlocked before the transition to the host system. Thus we have + two classes of secrets or credentials: one that can be unlocked during the entire runtime, and the + other that can only be used in the initrd.</para> + + <programlisting>$ openssl genpkey -algorithm RSA -pkeyopt rsa_keygen_bits:2048 -out tpm2-pcr-private.pem +.+........+.+........+.......+...+...+........+....+......+..+.......... +$ openssl rsa -pubout -in tpm2-pcr-private.pem -out tpm2-pcr-public.pem +$ openssl genpkey -algorithm RSA -pkeyopt rsa_keygen_bits:2048 -out tpm2-pcr-initrd-private.pem +..+.......++........+........+......+........+....+.....+.+..+.......... +$ openssl rsa -pubout -in tpm2-pcr-initrd-private.pem -out tpm2-pcr-initrd-public.pem +# ukify --output vmlinux-1.2.3.efi \ + --os-release=@os-release.txt \ + --cmdline=@cmdline.txt \ + --splash=splash.bmp \ + --devicetree=devicetree.dtb \ + --pcr-private-key=tpm2-pcr-private.pem \ + --pcr-public-key=tpm2-pcr-public.pem \ + --phases=enter-initrd,enter-initrd:leave-initrd,enter-initrd:leave-initrd:sysinit,enter-initrd:leave-initrd:sysinit:ready \ + --pcr-banks=sha1,sha256 \ + --pcr-private-key=tpm2-pcr-initrd-private.pem \ + --pcr-public-key=tpm2-pcr-initrd-public.pem \ + --phases=enter-initrd \ + vmlinux-1.2.3 initrd.cpio \ + --uname=1.2.3 ++ /usr/lib/systemd/systemd-measure sign --linux=vmlinux-1.2.3 \ +--osrel=os-release.txt --cmdline=cmdline.txt --dtb=devicetree.dtb \ +--splash=splash.bmp --initrd=initrd.cpio --bank=sha1 --bank=sha256 \ +--private-key=tpm2-pcr-private.pem --public-key=tpm2-pcr-public.pem \ +--phase=enter-initrd --phase=enter-initrd:leave-initrd \ +--phase=enter-initrd:leave-initrd:sysinit \ +--phase=enter-initrd:leave-initrd:sysinit:ready ++ /usr/lib/systemd/systemd-measure sign --linux=vmlinux-1.2.3 \ +--osrel=os-release.txt --cmdline=cmdline.txt --dtb=devicetree.dtb \ +--splash=splash.bmp --initrd=initrd.cpio --bank=sha1 --bank=sha256 \ +--private-key=tpm2-pcr-initrd-private.pem \ +--public-key=tpm2-pcr-initrd-public.pem \ +--phase=enter-initrd +Wrote unsigned vmlinux-1.2.3.efi + </programlisting> + + <para><command>ukify</command> prints out both invocations of <command>systemd-measure</command> as + informative output (the lines starting with <literal>+</literal>); this allows us to see how + <command>systemd-measure</command> is called. It then merges the output of both invocations into the + <literal>.pcrsig</literal> section. <command>systemd-measure</command> may also do this merge itself + using the <option>--append=</option> option.</para> + + <para>Note that in this example the <literal>.pcrpkey</literal> PE section contains the key specified + by the first <option>--pcr-private-key=</option> option, covering all boot phases. The + <literal>.pcrpkey</literal> section is used in the default policies of + <command>systemd-cryptenroll</command> and <command>systemd-creds</command>. To use the stricter policy + bound to <filename>tpm-pcr-initrd-public.pem</filename>, specify <option>--tpm2-public-key=</option> on + the command line of those tools.</para> + </example> + </refsect1> + + <refsect1> + <title>Exit status</title> + + <para>On success, 0 is returned, a non-zero failure code otherwise.</para> + </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>ukify</refentrytitle><manvolnum>1</manvolnum></citerefentry>, + <citerefentry><refentrytitle>systemd-creds</refentrytitle><manvolnum>1</manvolnum></citerefentry>, + <citerefentry><refentrytitle>systemd-cryptsetup@.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>, + <citerefentry><refentrytitle>systemd-pcrphase.service</refentrytitle><manvolnum>8</manvolnum></citerefentry> + </para> + </refsect1> + +</refentry> |