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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
- "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
+ "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd">
<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
<refentry id="systemd-stub" conditional='ENABLE_BOOTLOADER'
</refnamediv>
<refsynopsisdiv>
- <para><filename>/usr/lib/systemd/boot/efi/linuxx64.efi.stub</filename></para>
- <para><filename>/usr/lib/systemd/boot/efi/linuxia32.efi.stub</filename></para>
- <para><filename>/usr/lib/systemd/boot/efi/linuxaa64.efi.stub</filename></para>
- <para><filename><replaceable>ESP</replaceable>/.../<replaceable>foo</replaceable>.efi.extra.d/*.addon.efi</filename></para>
- <para><filename><replaceable>ESP</replaceable>/.../<replaceable>foo</replaceable>.efi.extra.d/*.cred</filename></para>
- <para><filename><replaceable>ESP</replaceable>/.../<replaceable>foo</replaceable>.efi.extra.d/*.raw</filename></para>
- <para><filename><replaceable>ESP</replaceable>/loader/addons/*.addon.efi</filename></para>
- <para><filename><replaceable>ESP</replaceable>/loader/credentials/*.cred</filename></para>
+ <para><simplelist>
+ <member><filename>/usr/lib/systemd/boot/efi/linuxx64.efi.stub</filename></member>
+ <member><filename>/usr/lib/systemd/boot/efi/linuxia32.efi.stub</filename></member>
+ <member><filename>/usr/lib/systemd/boot/efi/linuxaa64.efi.stub</filename></member>
+ <member><filename><replaceable>ESP</replaceable>/.../<replaceable>foo</replaceable>.efi.extra.d/*.addon.efi</filename></member>
+ <member><filename><replaceable>ESP</replaceable>/.../<replaceable>foo</replaceable>.efi.extra.d/*.cred</filename></member>
+ <member><filename><replaceable>ESP</replaceable>/.../<replaceable>foo</replaceable>.efi.extra.d/*.raw</filename></member>
+ <member><filename><replaceable>ESP</replaceable>/.../<replaceable>foo</replaceable>.efi.extra.d/*.sysext.raw</filename></member>
+ <member><filename><replaceable>ESP</replaceable>/.../<replaceable>foo</replaceable>.efi.extra.d/*.confext.raw</filename></member>
+ <member><filename><replaceable>ESP</replaceable>/loader/addons/*.addon.efi</filename></member>
+ <member><filename><replaceable>ESP</replaceable>/loader/credentials/*.cred</filename></member>
+ </simplelist></para>
</refsynopsisdiv>
<refsect1>
<!-- Let's keep this in the canonical order we also measure the sections by, i.e. as in
src/fundamental/uki.h's UnifiedSection enum -->
- <listitem><para>The ELF Linux kernel images will be looked for in the <literal>.linux</literal> PE
- section of the executed image.</para></listitem>
+ <listitem><para>A <literal>.linux</literal> section with the ELF Linux kernel image.</para></listitem>
- <listitem><para>OS release information, i.e. the
- <citerefentry><refentrytitle>os-release</refentrytitle><manvolnum>5</manvolnum></citerefentry> file of
- the OS the kernel belongs to, in the <literal>.osrel</literal> PE section.</para></listitem>
+ <listitem><para>An <literal>.osrel</literal> section with OS release information, i.e. the contents of
+ the <citerefentry><refentrytitle>os-release</refentrytitle><manvolnum>5</manvolnum></citerefentry> file
+ of the OS the kernel belongs to.</para></listitem>
- <listitem><para>The kernel command line to pass to the invoked kernel will be looked for in the
- <literal>.cmdline</literal> PE section.</para></listitem>
+ <listitem><para>A <literal>.cmdline</literal> section with the kernel command line to pass to the
+ invoked kernel.</para></listitem>
- <listitem><para>The initrd will be loaded from the <literal>.initrd</literal> PE
- section.</para></listitem>
+ <listitem><para>An <literal>.initrd</literal> section with the initrd.</para></listitem>
- <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 <literal>.ucode</literal> section with an initrd containing microcode, to be handed
+ to the kernel before any other initrd. This initrd must not be compressed.</para></listitem>
- <listitem><para>A compiled binary DeviceTree will be looked for in the <literal>.dtb</literal> PE
- section.</para></listitem>
+ <listitem><para>A <literal>.splash</literal> section with an image (in the Windows
+ <filename>.BMP</filename> format) to show on screen before invoking the kernel.</para></listitem>
- <listitem><para>Kernel version information, i.e. the output of <command>uname -r</command> for the
- kernel included in the UKI, in the <literal>.uname</literal> PE section.</para></listitem>
+ <listitem><para>A <literal>.dtb</literal> section with a compiled binary DeviceTree.</para></listitem>
+
+ <listitem><para>A <literal>.uname</literal> section with the kernel version information, i.e. the
+ output of <command>uname -r</command> for the kernel included in the <literal>.linux</literal>
+ section.</para></listitem>
- <listitem><para><ulink url="https://github.com/rhboot/shim/blob/main/SBAT.md">SBAT</ulink> revocation
- metadata, in the <literal>.sbat</literal> PE section.</para></listitem>
+ <listitem><para>An <literal>.sbat</literal> section with
+ <ulink url="https://github.com/rhboot/shim/blob/main/SBAT.md">SBAT</ulink> revocation
+ metadata.</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 <literal>.pcrsig</literal> section with a set of cryptographic signatures for the
+ expected TPM2 PCR values after the kernel has been booted, in JSON format. 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>
+ <listitem><para>A <literal>.pcrpkey</literal> section with a public key in the PEM format matching the
+ signature data in the <literal>.pcrsig</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 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>The contents of eight of these nine sections are measured into TPM PCR 11. It is otherwise not used
+ and thus the result can be pre-calculated without too much effort. The <literal>.pcrsig</literal> section
+ is not included in this PCR measurement, since it is supposed to contain signatures for the output 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
+ <para>When <literal>.pcrsig</literal> and/or <literal>.pcrpkey</literal> sections 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
<itemizedlist>
<listitem><para>For a kernel binary called <filename><replaceable>foo</replaceable>.efi</filename>, it
will look for files with the <filename>.cred</filename> suffix in a directory named
- <filename><replaceable>foo</replaceable>.efi.extra.d/</filename> next to it. A <command>cpio</command>
+ <filename><replaceable>foo</replaceable>.efi.extra.d/</filename> next to it. If the kernel binary
+ uses a counter for the purpose of
+ <ulink url="https://systemd.io/AUTOMATIC_BOOT_ASSESSMENT">Automatic Boot Assessment</ulink>, this
+ counter will be ignored. For example, <filename><replaceable>foo</replaceable>+3-0.efi</filename>
+ will look in directory <filename><replaceable>foo</replaceable>.efi.extra.d/</filename>.
+ A <command>cpio</command>
archive is generated from all files found that way, placing them in the
<filename>/.extra/credentials/</filename> directory of the initrd file hierarchy. The main initrd may
then access them in this directory. This is supposed to be used to store auxiliary, encrypted,
details on encrypted credentials. The generated <command>cpio</command> archive is measured into TPM
PCR 12 (if a TPM is present).</para></listitem>
- <listitem><para>Similarly, files <filename><replaceable>foo</replaceable>.efi.extra.d/*.raw</filename>
- are packed up in a <command>cpio</command> archive and placed in the <filename>/.extra/sysext/</filename>
- directory in the initrd file hierarchy. This is supposed to be used to pass additional system extension
- images to the initrd. See
+ <listitem><para>Similarly, files
+ <filename><replaceable>foo</replaceable>.efi.extra.d/*.sysext.raw</filename> are packed up in a
+ <command>cpio</command> archive and placed in the <filename>/.extra/sysext/</filename> directory in the
+ initrd file hierarchy. This is supposed to be used to pass additional system extension images to the
+ initrd. See
<citerefentry><refentrytitle>systemd-sysext</refentrytitle><manvolnum>8</manvolnum></citerefentry> for
details on system extension images. The generated <command>cpio</command> archive containing these
system extension images is measured into TPM PCR 13 (if a TPM is present).</para></listitem>
+ <!-- Note: the actual suffix we look for for sysexts is just *.raw (not *.sysext.raw), for
+ compatibility reasons with old versions. But we want people to name their system extensions
+ properly, hence we document the *.sysext.raw suffix only. -->
+
<listitem><para>Similarly, files
- <filename><replaceable>foo</replaceable>.efi.extra.d/*.addon.efi</filename>
- are loaded and verified as PE binaries, and a <literal>.cmdline</literal> section is parsed from them.
- In case Secure Boot is enabled, these files will be validated using keys in UEFI DB, Shim's DB or
- Shim's MOK, and will be rejected otherwise. Additionally, if the both the addon and the UKI contain a
- a <literal>.uname</literal> section, the addon will be rejected if they do not exactly match. It is
+ <filename><replaceable>foo</replaceable>.efi.extra.d/*.confext.raw</filename> are packed up in a
+ <command>cpio</command> archive and placed in the <filename>/.extra/confext/</filename> directory in
+ the initrd file hierarchy. This is supposed to be used to pass additional configuration extension
+ images to the initrd. See
+ <citerefentry><refentrytitle>systemd-confext</refentrytitle><manvolnum>8</manvolnum></citerefentry> for
+ details on configuration extension images. The generated <command>cpio</command> archive containing
+ these system extension images is measured into TPM PCR 12 (if a TPM is present).</para></listitem>
+
+ <listitem><para>Similarly, files
+ <filename><replaceable>foo</replaceable>.efi.extra.d/*.addon.efi</filename> are loaded and verified as
+ PE binaries, and a <literal>.cmdline</literal> section is parsed from them. Addons are supposed to be
+ used to pass additional kernel command line parameters or Devicetree blobs, regardless of the kernel
+ image being booted, for example to allow platform vendors to ship platform-specific
+ configuration.</para>
+
+ <para>In case Secure Boot is enabled, these files will be validated using keys in UEFI DB, Shim's DB or
+ Shim's MOK, and will be rejected otherwise. Additionally, if both the addon and the UKI contain a
+ <literal>.uname</literal> section, the addon will be rejected if they do not match exactly. It is
recommended to always add a <literal>.sbat</literal> section to all signed addons, so that they may be
revoked with a SBAT policy update, without requiring blocklisting via DBX/MOKX. The
- <citerefentry><refentrytitle>ukify</refentrytitle><manvolnum>1</manvolnum></citerefentry> tool will
- add a SBAT policy by default if none is passed when building addons. For more information on SBAT see
- <ulink url="https://github.com/rhboot/shim/blob/main/SBAT.md">Shim's documentation</ulink>.
- Addons are supposed to be used to pass additional kernel command line parameters, regardless of the
- kernel image being booted, for example to allow platform vendors to ship platform-specific
- configuration. The loaded command line addon files are sorted, loaded, measured into TPM PCR 12 (if a
- TPM is present) and appended to the kernel command line. UKI command line options are listed first,
- then options from addons in <filename>/loader/addons/*.addon.efi</filename> are appended next, and
- finally UKI-specific addons are appended last. Addons are always loaded in the same order based on the
- filename, so that, given the same set of addons, the same set of measurements can be expected in
- PCR12, however note that the filename is not protected by the PE signature, and as such an attacker
- with write access to the ESP could potentially rename these files to change the order in which they
- are loaded, in a way that could alter the functionality of the kernel, as some options might be order
- dependent. If you sign such addons, you should pay attention to the PCR12 values and make use of an
- attestation service so that improper use of your signed addons can be detected and dealt with using
+ <citerefentry><refentrytitle>ukify</refentrytitle><manvolnum>1</manvolnum></citerefentry> tool will add
+ a SBAT policy by default if none is passed when building addons. For more information on SBAT see
+ <ulink url="https://github.com/rhboot/shim/blob/main/SBAT.md">Shim documentation</ulink>.</para>
+
+ <para>Addon files are sorted, loaded, and measured into TPM PCR 12 (if a TPM is present) and appended
+ to the kernel command line. UKI command line options are listed first, then options from addons in
+ <filename>/loader/addons/*.addon.efi</filename>, and finally UKI-specific addons. Device tree blobs are
+ loaded and measured following the same algorithm. Addons are always loaded in the same order based on
+ the filename, so that, given the same set of addons, the same set of measurements can be expected in
+ PCR12. However, note that the filename is not protected by the PE signature, and as such an attacker
+ with write access to the ESP could potentially rename these files to change the order in which they are
+ loaded, in a way that could alter the functionality of the kernel, as some options might be
+ order-dependent. If you sign such addons, you should pay attention to the PCR12 values and make use of
+ an attestation service so that improper use of your signed addons can be detected and dealt with using
one of the aforementioned revocation mechanisms.</para></listitem>
<listitem><para>Files <filename>/loader/credentials/*.cred</filename> are packed up in a
measured into TPM PCR 12 (if a TPM is present).</para></listitem>
<listitem><para>Additionally, files <filename>/loader/addons/*.addon.efi</filename> are loaded and
- verified as PE binaries, and a <literal>.cmdline</literal> section is parsed from them. This is
- supposed to be used to pass additional command line parameters to the kernel, regardless of the kernel
- being booted.</para></listitem>
+ verified as PE binaries, and <literal>.cmdline</literal> and/or <literal>.dtb</literal> sections are
+ parsed from them. This is supposed to be used to pass additional command line parameters or Devicetree
+ blobs to the kernel, regardless of the kernel being booted.</para></listitem>
</itemizedlist>
<para>These mechanisms may be used to parameterize and extend trusted (i.e. signed), immutable initrd
core kernel, the embedded initrd and kernel command line (see above for a full list).</para>
<para>Also note that the Linux kernel will measure all initrds it receives into TPM PCR 9. This means
- every type of initrd will be measured two or three times: the initrd embedded in the kernel image will be
- measured to PCR 4, PCR 9 and PCR 11; the initrd synthesized from credentials will be measured to both PCR
- 9 and PCR 12; the initrd synthesized from system extensions will be measured to both PCR 4 and PCR
- 9. Let's summarize the OS resources and the PCRs they are measured to:</para>
+ every type of initrd will be measured two or three times: the initrds embedded in the kernel image will be
+ measured to PCR 4, PCR 9 and PCR 11; the initrd synthesized from credentials (and the one synthesized
+ from configuration extensions) will be measured to both PCR 9 and PCR 12; the initrd synthesized from
+ system extensions will be measured to both PCR 4 and PCR 9. Let's summarize the OS resources and the PCRs
+ they are measured to:</para>
<table>
<title>OS Resource PCR Summary</title>
<entry>4 + 9 + 11</entry>
</row>
+ <row>
+ <entry>Microcode initrd (embedded in unified PE binary)</entry>
+ <entry>4 + 9 + 11</entry>
+ </row>
+
<row>
<entry>Default kernel command line (embedded in unified PE binary)</entry>
<entry>4 + 11</entry>
<entry>System Extensions (synthesized initrd from companion files)</entry>
<entry>9 + 13</entry>
</row>
+
+ <row>
+ <entry>Configuration Extensions (synthesized initrd from companion files)</entry>
+ <entry>9 + 12</entry>
+ </row>
</tbody>
</tgroup>
</table>
<varlistentry>
<term><varname>StubPcrInitRDSysExts</varname></term>
- <listitem><para>The PCR register index the systemd extensions for the initrd, which are picked up
- from the file system the kernel image is located on. Formatted as decimal ASCII string (e.g.
+ <listitem><para>The PCR register index the system extensions for the initrd, which are picked up from
+ the file system the kernel image is located on. Formatted as decimal ASCII string (e.g.
<literal>13</literal>). This variable is set if a measurement was successfully completed, and remains
unset otherwise.</para>
<xi:include href="version-info.xml" xpointer="v252"/></listitem>
</varlistentry>
+
+ <varlistentry>
+ <term><varname>StubPcrInitRDConfExts</varname></term>
+
+ <listitem><para>The PCR register index the configuration extensions for the initrd, which are picked
+ up from the file system the kernel image is located on. Formatted as decimal ASCII string (e.g.
+ <literal>12</literal>). This variable is set if a measurement was successfully completed, and remains
+ unset otherwise.</para>
+
+ <xi:include href="version-info.xml" xpointer="v255"/></listitem>
+ </varlistentry>
</variablelist>
<para>Note that some of the variables above may also be set by the boot loader. The stub will only set
<varlistentry>
<term><filename>/</filename></term>
- <listitem><para>The main initrd from the <literal>.initrd</literal> PE section of the unified kernel image.</para>
+ <listitem><para>The main initrd from the <literal>.initrd</literal> PE section of the unified kernel
+ image.</para>
<xi:include href="version-info.xml" xpointer="v252"/></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
+ <listitem><para>Similarly, 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>
</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
+ <term><filename>/.extra/sysext/*.sysext.raw</filename></term>
+ <listitem><para>System extension image files (suffix <literal>.sysext.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>
<xi:include href="version-info.xml" xpointer="v252"/></listitem>
</varlistentry>
+ <varlistentry>
+ <term><filename>/.extra/confext/*.confext.raw</filename></term>
+ <listitem><para>Configuration extension image files (suffix <literal>.confext.raw</literal>) that are
+ placed next to the unified kernel image (as described above) are copied into the
+ <filename>/.extra/confext/</filename> directory in the initrd execution environment.</para>
+
+ <xi:include href="version-info.xml" xpointer="v255"/></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>
+ <filename>/.extra/tpm2-pcr-signature.json</filename> file in the initrd execution environment.</para>
<xi:include href="version-info.xml" xpointer="v252"/></listitem>
</varlistentry>
<title>SMBIOS Type 11 Strings</title>
<para><command>systemd-stub</command> can be configured using SMBIOS Type 11 strings. Applicable strings
- consist of a name, followed by <literal>=</literal>, followed by the value.
+ consist of a name, followed by <literal>=</literal>, followed by the value. Unless
+ <command>systemd-stub</command> detects it is running inside a confidential computing environment,
<command>systemd-stub</command> will search the table for a string with a specific name, and if found,
use its value. The following strings are read:</para>
<refsect1>
<title>See Also</title>
- <para>
- <citerefentry><refentrytitle>systemd-boot</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
- <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
- <citerefentry><refentrytitle>systemd-creds</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
- <citerefentry><refentrytitle>systemd-sysext</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
- <ulink url="https://uapi-group.org/specifications/specs/boot_loader_specification">Boot Loader Specification</ulink>,
- <ulink url="https://systemd.io/BOOT_LOADER_INTERFACE">Boot Loader Interface</ulink>,
- <citerefentry><refentrytitle>ukify</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
- <citerefentry><refentrytitle>systemd-measure</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
- <ulink url="https://systemd.io/TPM2_PCR_MEASUREMENTS">TPM2 PCR Measurements Made by systemd</ulink>
- </para>
+ <para><simplelist type="inline">
+ <member><citerefentry><refentrytitle>systemd-boot</refentrytitle><manvolnum>7</manvolnum></citerefentry></member>
+ <member><citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry></member>
+ <member><citerefentry><refentrytitle>systemd-creds</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
+ <member><citerefentry><refentrytitle>systemd-sysext</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
+ <member><ulink url="https://uapi-group.org/specifications/specs/boot_loader_specification">Boot Loader Specification</ulink></member>
+ <member><ulink url="https://systemd.io/BOOT_LOADER_INTERFACE">Boot Loader Interface</ulink></member>
+ <member><citerefentry><refentrytitle>ukify</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
+ <member><citerefentry><refentrytitle>systemd-measure</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
+ <member><ulink url="https://systemd.io/TPM2_PCR_MEASUREMENTS">TPM2 PCR Measurements Made by systemd</ulink></member>
+ </simplelist></para>
</refsect1>
</refentry>
projects / thirdparty / systemd.git / blobdiff