<citerefentry><refentrytitle>systemd-stub</refentrytitle><manvolnum>7</manvolnum></citerefentry> is
booted up. It accepts paths to the ELF kernel image file, initial ram disk image file, devicetree file,
kernel command line file,
- <citerefentry><refentrytitle>os-release</refentrytitle><manvolnum>5</manvolnum></citerefentry> file, and
- boot splash 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>
+ <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>
</refsect1>
<refsect1>
<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>, see below. Only <option>--linux=</option> is
- mandatory. (Alternatively, specify <option>--current</option> to use the current values of PCR
- register 11 instead.)</para></listitem>
+ <option>--splash=</option>, <option>--dtb=</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></listitem>
</varlistentry>
<varlistentry>
<term><option>--initrd=PATH</option></term>
<term><option>--splash=PATH</option></term>
<term><option>--dtb=PATH</option></term>
+ <term><option>--pcrpkey=PATH</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
<term><option>--public-key=PATH</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></listitem>
+ 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></listitem>
</varlistentry>
<varlistentry>
</example>
<example>
- <title>Generate a private/public key pair, and a unified kernel image, and a TPM PCR 11 signature for it</title>
+ <title>Generate a private/public key pair, and 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
-# objcopy \
- --add-section .linux=vmlinux --change-section-vma .linux=0x2000000 \
- --add-section .osrel=os-release.txt --change-section-vma .osrel=0x20000 \
- --add-section .cmdline=cmdline.txt --change-section-vma .cmdline=0x30000 \
- --add-section .initrd=initrd.cpio --change-section-vma .initrd=0x3000000 \
- --add-section .splash=splash.bmp --change-section-vma .splash=0x100000 \
- --add-section .dtb=devicetree.dtb --change-section-vma .dtb=0x40000 \
- /usr/lib/systemd/boot/efi/linuxx64.efi.stub \
- foo.efi
# systemd-measure sign \
--linux=vmlinux \
--osrel=os-release.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</programlisting>
+ --public-key=tpm2-pcr-public.pem > tpm2-pcr-signature.json
+# objcopy \
+ --add-section .linux=vmlinux --change-section-vma .linux=0x2000000 \
+ --add-section .osrel=os-release.txt --change-section-vma .osrel=0x20000 \
+ --add-section .cmdline=cmdline.txt --change-section-vma .cmdline=0x30000 \
+ --add-section .initrd=initrd.cpio --change-section-vma .initrd=0x3000000 \
+ --add-section .splash=splash.bmp --change-section-vma .splash=0x100000 \
+ --add-section .dtb=devicetree.dtb --change-section-vma .dtb=0x40000 \
+ --add-section .pcrsig=tpm2-pcr-signature.json --change-section-vma .splash=0x80000 \
+ --add-section .pcrpkey=tpm2-pcr-public.pem --change-section-vma .splash=0x90000 \
+ /usr/lib/systemd/boot/efi/linuxx64.efi.stub \
+ foo.efi</programlisting>
<para>Later on, enroll the signed PCR policy on a LUKS volume:</para>
<para>And then unlock the device with the signature:</para>
<programlisting># /usr/lib/systemd/systemd-cryptsetup attach myvolume /dev/sda5 - tpm2-device=auto,tpm2-signature=/path/to/tpm2-pcr-signature.json</programlisting>
+
+ <para>Note that when the generated unified kernel image <filename>foo.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>
</refsect1>
<listitem><para>A boot splash (in Windows <filename>.BMP</filename> format) to show on screen before
invoking the kernel will be looked for in the <literal>.splash</literal> PE section.</para></listitem>
+
+ <listitem><para>A set of cryptographic signatures for expected TPM2 PCR values when this kernel is
+ booted, in JSON format, in the <literal>.pcrsig</literal> section. This is useful for implementing TPM2
+ policies that bind disk encryption and similar to kernels that are signed by a specific
+ key.</para></listitem>
+
+ <listitem><para>A public key in PEM format matching this TPM2 PCR signature data in the
+ <literal>.pcrpkey</literal> section.</para></listitem>
</itemizedlist>
<para>If UEFI SecureBoot is enabled and the <literal>.cmdline</literal> section is present in the executed
DeviceTree in the corresponding EFI configuration table. systemd-stub will ask the firmware via the
<literal>EFI_DT_FIXUP_PROTOCOL</literal> for hardware specific fixups to the DeviceTree.</para>
- <para>The contents of these six PE sections are measured into TPM PCR 11, that is otherwise not
- used. Thus, it can be pre-calculated without too much effort.</para>
+ <para>The contents of seven of these eight PE sections are measured into TPM PCR 11, that is otherwise
+ not used. Thus, it can be pre-calculated without too much effort. The <literal>.pcrsig</literal> section
+ is not included in this PCR measurement, since it's supposed to contain signatures for the expected
+ results for these measurements, i.e. of the outputs of the measurement operation, and thus cannot also be
+ input to it.</para>
+
+ <para>When <literal>.pcrsig</literal> and/or <literal>.pcrpkey</literal> are present in a unified kernel
+ image their contents are passed to the booted kernel in an synthetic initrd cpio archive that places them in the
+ <filename>/.extra/tpm2-pcr-signature.json</filename> and
+ <filename>/.extra/tpm2-pcr-public-key.pem</filename> files. Typically, a
+ <citerefentry><refentrytitle>tmpfiles.d</refentrytitle><manvolnum>5</manvolnum></citerefentry> line then
+ ensures they are copied into <filename>/run/systemd/tpm2-pcr-signature.json</filename> and
+ <filename>/run/systemd/tpm2-pcr-public-key.pem</filename> where they remain accessible even after the
+ system transitions out of the initrd environment into the host file system. Tools such
+ <citerefentry><refentrytitle>systemd-cryptsetup@.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>systemd-cryptenroll</refentrytitle><manvolnum>1</manvolnum></citerefentry>
+ and <citerefentry><refentrytitle>systemd-creds</refentrytitle><manvolnum>1</manvolnum></citerefentry>
+ will automatically use files present under these paths to unlock protected resources (encrypted storage
+ or credentials) or bind encryption to booted kernels.</para>
</refsect1>
<refsect1>
</row>
<row>
- <entry>Boot splash (embedded in the unified PE binary)</entry>
+ <entry>Core kernel code (embedded in unified PE binary)</entry>
<entry>4 + 11</entry>
</row>
<row>
- <entry>Core kernel code (embedded in unified PE binary)</entry>
+ <entry>OS release information (embedded in the unified PE binary)</entry>
<entry>4 + 11</entry>
</row>
<entry>12</entry>
</row>
+ <row>
+ <entry>Boot splash (embedded in the unified PE binary)</entry>
+ <entry>4 + 11</entry>
+ </row>
+
+ <row>
+ <entry>TPM2 PCR signature JSON (embedded in unified PE binary, synthesized into initrd)</entry>
+ <entry>4 + 9</entry>
+ </row>
+
+ <row>
+ <entry>TPM2 PCR PEM public key (embedded in unified PE binary, synthesized into initrd)</entry>
+ <entry>4 + 9 + 11</entry>
+ </row>
+
<row>
<entry>Credentials (synthesized initrd from companion files)</entry>
<entry>9 + 12</entry>
url="https://systemd.io/BOOT_LOADER_INTERFACE">Boot Loader Interface</ulink>.</para>
</refsect1>
+ <refsect1>
+ <title>initrd Resources</title>
+
+ <para>The following resources are passed as initrd cpio archives to the booted kernel, and thus make up
+ the initial file system hierarchy in the initrd execution environment:</para>
+
+ <variablelist>
+ <varlistentry>
+ <term><filename>/</filename></term>
+
+ <listitem><para>The main initrd from the <literal>.initrd</literal> PE section of the unified kernel image.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><filename>/.extra/credentials/*.cred</filename></term>
+ <listitem><para>Credential files (suffix <literal>.cred</literal>) that are placed next to the
+ unified kernel image (as described above) are copied into the
+ <filename>/.extra/credentials/</filename> directory in the initrd execution
+ environment.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><filename>/.extra/global_credentials/*.cred</filename></term>
+ <listitem><para>Similar, credential files in the <filename>/loader/credentials/</filename> directory
+ in the file system the unified kernel image is placed in are copied into the
+ <filename>/.extra/global_credentials/</filename> directory in the initrd execution
+ environment.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><filename>/.extra/sysext/*.raw</filename></term>
+ <listitem><para>System extension image files (suffix <literal>.raw</literal>) that are placed next to
+ the unified kernel image (as described above) are copied into the
+ <filename>/.extra/sysext/</filename> directory in the initrd execution environment.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><filename>/.extra/tpm2-pcr-signature.json</filename></term>
+ <listitem><para>The TPM2 PCR signature JSON object included in the <literal>.pcrsig</literal> PE
+ section of the unified kernel image is copied into the
+ <filename>/.extra/tpm2-pcr-signature.json</filename> file in the initrd execution
+ environment.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><filename>/.extra/tpm2-pcr-pkey.pem</filename></term>
+ <listitem><para>The PEM public key included in the <literal>.pcrpkey</literal> PE section of the
+ unified kernel image is copied into the <filename>/.extra/tpm2-pcr-public-key.pem</filename> file in
+ the initrd execution environment.</para></listitem>
+ </varlistentry>
+ </variablelist>
+
+ <para>Note that all these files are located in the <literal>tmpfs</literal> file system the kernel sets
+ up for the initrd file hierarchy and are thus lost when the system transitions from the initrd execution
+ environment into the host file system. If these resources shall be kept around over this transition they
+ need to be copied to a place that survives the transition first, for example via a suitable
+ <citerefentry><refentrytitle>tmpfiles.d</refentrytitle><manvolnum>5</manvolnum></citerefentry> line. By
+ default, this is done for the TPM2 PCR signature and public key files.</para>
+ </refsect1>
+
<refsect1>
<title>Assembling Kernel Images</title>
<para>This expects a pair of X.509 private key and certificate as parameters and then signs the UEFI PE
executable we generated above for UEFI SecureBoot and generates a signed UEFI PE executable as
result.</para>
+
+ <para>See
+ <citerefentry><refentrytitle>systemd-measure</refentrytitle><manvolnum>1</manvolnum></citerefentry> for
+ an example involving the <literal>.pcrsig</literal> and <literal>.pcrpkey</literal> sections.</para>
</refsect1>
<refsect1>
<ulink url="https://systemd.io/BOOT_LOADER_SPECIFICATION">Boot Loader Specification</ulink>,
<ulink url="https://systemd.io/BOOT_LOADER_INTERFACE">Boot Loader Interface</ulink>,
<citerefentry project='man-pages'><refentrytitle>objcopy</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
- <citerefentry project='archlinux'><refentrytitle>sbsign</refentrytitle><manvolnum>1</manvolnum></citerefentry>
+ <citerefentry project='archlinux'><refentrytitle>sbsign</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>systemd-measure</refentrytitle><manvolnum>1</manvolnum></citerefentry>
</para>
</refsect1>
</refentry>
projects / thirdparty / systemd.git / commitdiff
