mirror of
https://github.com/systemd/systemd
synced 2024-11-05 18:25:39 +00:00
551 lines
29 KiB
XML
551 lines
29 KiB
XML
<?xml version='1.0'?> <!--*-nxml-*-->
|
|
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
|
|
"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'
|
|
xmlns:xi="http://www.w3.org/2001/XInclude">
|
|
<refentryinfo>
|
|
<title>systemd-stub</title>
|
|
<productname>systemd</productname>
|
|
</refentryinfo>
|
|
|
|
<refmeta>
|
|
<refentrytitle>systemd-stub</refentrytitle>
|
|
<manvolnum>7</manvolnum>
|
|
</refmeta>
|
|
|
|
<refnamediv>
|
|
<refname>systemd-stub</refname>
|
|
<refname>sd-stub</refname>
|
|
<refname>linuxx64.efi.stub</refname>
|
|
<refname>linuxia32.efi.stub</refname>
|
|
<refname>linuxaa64.efi.stub</refname>
|
|
<refpurpose>A simple UEFI kernel boot stub</refpurpose>
|
|
</refnamediv>
|
|
|
|
<refsynopsisdiv>
|
|
<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>
|
|
<title>Description</title>
|
|
|
|
<para><command>systemd-stub</command> (stored in per-architecture files
|
|
<filename>linuxx64.efi.stub</filename>, <filename>linuxia32.efi.stub</filename>,
|
|
<filename>linuxaa64.efi.stub</filename> on disk) is a simple UEFI boot stub. An UEFI boot stub is
|
|
attached to a Linux kernel binary image, and is a piece of code that runs in the UEFI firmware
|
|
environment before transitioning into the Linux kernel environment. The UEFI boot stub ensures a Linux
|
|
kernel is executable as regular UEFI binary, and is able to do various preparations before switching the
|
|
system into the Linux world.</para>
|
|
|
|
<para>The UEFI boot stub looks for various resources for the kernel invocation inside the UEFI PE binary
|
|
itself. This allows combining various resources inside a single PE binary image (usually called "Unified
|
|
Kernel Image", or "UKI" for short), which may then be signed via UEFI SecureBoot as a whole, covering all
|
|
individual resources at once. Specifically it may include:</para>
|
|
|
|
<itemizedlist>
|
|
<!-- 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>A <literal>.linux</literal> section with the ELF Linux kernel image.</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>A <literal>.cmdline</literal> section with the kernel command line to pass to the
|
|
invoked kernel.</para></listitem>
|
|
|
|
<listitem><para>An <literal>.initrd</literal> section with the initrd.</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 <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>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>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 <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 <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
|
|
image, any attempts to override the kernel command line by passing one as invocation parameters to the
|
|
EFI binary are ignored. Thus, in order to allow overriding the kernel command line, either disable UEFI
|
|
SecureBoot, or don't include a kernel command line PE section in the kernel image file. If a command line
|
|
is accepted via EFI invocation parameters to the EFI binary it is measured into TPM PCR 12 (if a TPM is
|
|
present).</para>
|
|
|
|
<para>If a DeviceTree is embedded in the <literal>.dtb</literal> section, it replaces an existing
|
|
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 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> 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
|
|
<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>
|
|
|
|
<para>For further details about the UKI concept, see the <ulink
|
|
url="https://uapi-group.org/specifications/specs/unified_kernel_image/">UKI specification</ulink>.</para>
|
|
</refsect1>
|
|
|
|
<refsect1>
|
|
<title>Companion Files</title>
|
|
|
|
<para>The <command>systemd-stub</command> UEFI boot stub automatically collects three types of auxiliary
|
|
companion files optionally placed in drop-in directories on the same partition as the EFI binary,
|
|
dynamically generates <command>cpio</command> initrd archives from them, and passes them to the kernel.
|
|
Specifically:</para>
|
|
|
|
<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. 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,
|
|
authenticated credentials for use with <varname>LoadCredentialEncrypted=</varname> in the UEFI System
|
|
Partition. See
|
|
<citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>
|
|
and
|
|
<citerefentry><refentrytitle>systemd-creds</refentrytitle><manvolnum>1</manvolnum></citerefentry>
|
|
for
|
|
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/*.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/*.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 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
|
|
<command>cpio</command> archive and placed in the <filename>/.extra/global_credentials/</filename>
|
|
directory of the initrd file hierarchy. This is supposed to be used to pass additional credentials to
|
|
the initrd, regardless of the kernel being booted. The generated <command>cpio</command> archive is
|
|
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 <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
|
|
images in a reasonably safe way: all data they contain is measured into TPM PCRs. On access they should be
|
|
further validated: in case of the credentials case by encrypting/authenticating them via TPM, as exposed
|
|
by <command>systemd-creds encrypt -T</command> (see
|
|
<citerefentry><refentrytitle>systemd-creds</refentrytitle><manvolnum>1</manvolnum></citerefentry> for
|
|
details); in case of the system extension images by using signed Verity images.</para>
|
|
</refsect1>
|
|
|
|
<refsect1>
|
|
<title>TPM PCR Notes</title>
|
|
|
|
<para>Note that when a unified kernel using <command>systemd-stub</command> is invoked the firmware will
|
|
measure it as a whole to TPM PCR 4, covering all embedded resources, such as the stub code itself, the
|
|
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 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>
|
|
|
|
<tgroup cols='2' align='left' colsep='1' rowsep='1'>
|
|
<colspec colname="pcr" />
|
|
<colspec colname="definition" />
|
|
|
|
<thead>
|
|
<row>
|
|
<entry>OS Resource</entry>
|
|
<entry>Measurement PCR</entry>
|
|
</row>
|
|
</thead>
|
|
|
|
<tbody>
|
|
<row>
|
|
<entry><command>systemd-stub</command> code (the entry point of the unified PE binary)</entry>
|
|
<entry>4</entry>
|
|
</row>
|
|
|
|
<row>
|
|
<entry>Core kernel code (embedded in unified PE binary)</entry>
|
|
<entry>4 + 11</entry>
|
|
</row>
|
|
|
|
<row>
|
|
<entry>OS release information (embedded in the unified PE binary)</entry>
|
|
<entry>4 + 11</entry>
|
|
</row>
|
|
|
|
<row>
|
|
<entry>Main initrd (embedded in unified PE binary)</entry>
|
|
<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>
|
|
</row>
|
|
|
|
<row>
|
|
<entry>Overridden kernel command line</entry>
|
|
<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>
|
|
</row>
|
|
|
|
<row>
|
|
<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>
|
|
</refsect1>
|
|
|
|
<refsect1>
|
|
<title>EFI Variables</title>
|
|
|
|
<para>The following EFI variables are defined, set and read by <command>systemd-stub</command>, under the
|
|
vendor UUID <literal>4a67b082-0a4c-41cf-b6c7-440b29bb8c4f</literal>, for communication between the boot
|
|
stub and the OS:</para>
|
|
|
|
<variablelist class='efi-variables'>
|
|
<varlistentry>
|
|
<term><varname>LoaderDevicePartUUID</varname></term>
|
|
|
|
<listitem><para>Contains the partition UUID of the EFI System Partition the EFI image was run
|
|
from. <citerefentry><refentrytitle>systemd-gpt-auto-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>
|
|
uses this information to automatically find the disk booted from, in order to discover various other
|
|
partitions on the same disk automatically.</para>
|
|
|
|
<xi:include href="version-info.xml" xpointer="v250"/></listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>LoaderFirmwareInfo</varname></term>
|
|
<term><varname>LoaderFirmwareType</varname></term>
|
|
|
|
<listitem><para>Brief firmware information. Use
|
|
<citerefentry><refentrytitle>bootctl</refentrytitle><manvolnum>1</manvolnum></citerefentry> to view this
|
|
data.</para>
|
|
|
|
<xi:include href="version-info.xml" xpointer="v250"/></listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>LoaderImageIdentifier</varname></term>
|
|
|
|
<listitem><para>The path of EFI executable, relative to the EFI System Partition's root
|
|
directory. Use
|
|
<citerefentry><refentrytitle>bootctl</refentrytitle><manvolnum>1</manvolnum></citerefentry> to view
|
|
this data.</para>
|
|
|
|
<xi:include href="version-info.xml" xpointer="v250"/></listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>StubInfo</varname></term>
|
|
|
|
<listitem><para>Brief stub information. Use
|
|
<citerefentry><refentrytitle>bootctl</refentrytitle><manvolnum>1</manvolnum></citerefentry> to view
|
|
this data.</para>
|
|
|
|
<xi:include href="version-info.xml" xpointer="v250"/></listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>StubPcrKernelImage</varname></term>
|
|
|
|
<listitem><para>The PCR register index the kernel image, initrd image, boot splash, devicetree
|
|
database, and the embedded command line are measured into, formatted as decimal ASCII string (e.g.
|
|
<literal>11</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>StubPcrKernelParameters</varname></term>
|
|
|
|
<listitem><para>The PCR register index the kernel command line and credentials are measured into,
|
|
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="v252"/></listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>StubPcrInitRDSysExts</varname></term>
|
|
|
|
<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
|
|
them if they aren't set already. Some of these variables are defined by the <ulink
|
|
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>
|
|
|
|
<xi:include href="version-info.xml" xpointer="v252"/></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>
|
|
|
|
<xi:include href="version-info.xml" xpointer="v252"/></listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><filename>/.extra/global_credentials/*.cred</filename></term>
|
|
<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>
|
|
|
|
<xi:include href="version-info.xml" xpointer="v252"/></listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<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>
|
|
|
|
<xi:include href="version-info.xml" xpointer="v252"/></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>
|
|
|
|
<xi:include href="version-info.xml" xpointer="v252"/></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>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. 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>
|
|
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term><varname>io.systemd.stub.kernel-cmdline-extra</varname></term>
|
|
<listitem><para>If set, the value of this string is added to the list of kernel command line
|
|
arguments that are measured in PCR12 and passed to the kernel.</para>
|
|
|
|
<xi:include href="version-info.xml" xpointer="v254"/></listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
</refsect1>
|
|
|
|
<refsect1>
|
|
<title>Assembling Kernel Images</title>
|
|
|
|
<para>In order to assemble a bootable Unified Kernel Image from various components as described above, use
|
|
<citerefentry><refentrytitle>ukify</refentrytitle><manvolnum>1</manvolnum></citerefentry>.</para>
|
|
</refsect1>
|
|
|
|
<refsect1>
|
|
<title>See Also</title>
|
|
<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>
|