mkosi: update arch commit reference

[thirdparty/systemd.git] / man / systemd-stub.xml

diff --git a/man/systemd-stub.xml b/man/systemd-stub.xml
index b211339076714e1a66377bbd787fabfa8215953d..0bdf8f3139bc77d8532249a2c2a351a1ee602f6a 100644 (file)
--- a/man/systemd-stub.xml
+++ b/man/systemd-stub.xml
@@ -1,6 +1,6 @@
 <?xml version='1.0'?> <!--*-nxml-*-->
 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
 <?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">
+  "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'
 <!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
 
 <refentry id="systemd-stub" conditional='ENABLE_BOOTLOADER'


@@ -25,14 +25,18 @@
   </refnamediv>
 
   <refsynopsisdiv>
   </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>
   </refsynopsisdiv>
 
   <refsect1>


@@ -49,66 +53,76 @@
     <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
     <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>
+    individual resources at once. Specifically it may include the following PE sections:</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 -->
 
 
     <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>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. (Required)</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>A <literal>.dtb</literal> section with a compiled binary DeviceTree.</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>.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>
 
     </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 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
+    <para>Generally, the sections above should appear at most once in a UKI. That said, a concept of
+    "profiles" is defined, that allows multiple sets of these sections to exist in a single UKI file, of
+    which one can be selected at boot. For this an additional PE section <literal>.profile</literal> is
+    defined which can be used as separator between multiple sets of these settings. The
+    <literal>.profile</literal> section itself may contain meta-information about the section, and follows a
+    similar structure as the contents of the <literal>.osrel</literal> section. For further details about
+    multi-profile UKIs, see below.</para> <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 11 of these 12 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. If an UKI contains multiple profiles, only
+    the PE sections of the selected profile (and those of the base profile, except if overridden) are
+    measured.</para>
+
+    <para>If non-zero, the selected numeric profile is measured into PCR 12.</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>/.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


@@ -119,12 +133,15 @@
     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>
     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>
 
   </refsect1>
 
   <refsect1>
     <title>Companion Files</title>
 

-    <para>The <command>systemd-stub</command> UEFI boot stub automatically collects two types of auxiliary
+    <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>
     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>


@@ -132,7 +149,12 @@
     <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
     <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,
       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,


@@ -145,37 +167,56 @@
       details on encrypted credentials. The generated <command>cpio</command> archive is measured into TPM
       PCR 12 (if a TPM is present).</para></listitem>
 
       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>
 
       <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
       <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/*.addon.efi</filename> are loaded and verified as
+      PE binaries, and a <literal>.cmdline</literal> or <literal>.ucode</literal> section is parsed from them.
+      Addons are supposed to be used to pass additional kernel command line parameters, or Devicetree blobs,
+      and microcode updates, 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
       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. Microcode addons are passed to the kernel in inverse
+      order (UKI specific addons, global addons, UKI embedded section). This is because the microcode update
+      driver stops on the first matching filename. 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
       one of the aforementioned revocation mechanisms.</para></listitem>
 
       <listitem><para>Files <filename>/loader/credentials/*.cred</filename> are packed up in a


@@ -185,9 +226,10 @@
       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
       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>, <literal>.dtb</literal> and/or
+      <literal>.ucode</literal>sections are parsed from them. This is supposed to be used to pass additional
+      command line parameters, Devicetree blobs and microcode updates 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
     </itemizedlist>
 
     <para>These mechanisms may be used to parameterize and extend trusted (i.e. signed), immutable initrd


@@ -198,18 +240,124 @@
     details); in case of the system extension images by using signed Verity images.</para>
   </refsect1>
 
     details); in case of the system extension images by using signed Verity images.</para>
   </refsect1>
 

+  <refsect1>
+    <title>Multi-Profile UKIs</title>
+
+    <para>In many contexts it is useful to allow invocation of a single UKI in multiple different modes (or
+    "profiles") without compromising the cryptographic integrity, measurements and so on of the boot
+    process. For example, a single UKI might provide three distinct profiles: a regular boot one, one that
+    invokes a "factory reset" operation, and one that boots into a storage target mode (as in
+    <citerefentry><refentrytitle>systemd-storagetm.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>). Each
+    profile would then use the same <literal>.linux</literal> and <literal>.initrd</literal> sections, but would
+    have a separate <literal>.cmdline</literal> section. For example the latter two profiles would extend the
+    regular kernel command line with <literal>systemd.unit=factory-reset.target</literal> or
+    <literal>rd.systemd.unit=storagetm.target</literal>.</para>
+
+    <para>A single UKI may support multiple profiles by means of the special <literal>.profile</literal> PE
+    section. This section acts as separator between the PE sections of the individual
+    profiles. <literal>.profile</literal> PE sections hence may appear multiple times in a single UKI, and
+    the other PE sections listed above may appear multiple times too, if <literal>.profile</literal> are
+    used, but only once before the first <literal>.profile</literal> section, once between each subsequent
+    pair, and once after the last appearance of <literal>.profile</literal>. The sections listed before the
+    first <literal>.profile</literal> are considered the "base" profile of the UKI. Each
+    <literal>.profile</literal> section then introduces a new profile, which are numbered starting from
+    zero. The PE sections following each <literal>.profile</literal> are specific to that profile. When
+    booting into a specific profile the base section's profiles are used in combination with the specific
+    profile's sections: if the same section is defined in both, the per-profile section overrides the base
+    profile's version, otherwise the per-profile sections is used together with the base profile
+    sections.</para> <para>A UKI that contains no <literal>.profile</literal> is consider equivalent to one
+    that just contains a single <literal>.profile</literal>, as having only a single profile @0.</para>
+
+    <para>Here's a simple example for a multi-profile UKI's sections, inspired by the setup suggested above:</para>
+
+    <table>
+      <title>Multi-Profile UKI Example</title>
+
+      <tgroup cols='2' align='left' colsep='1' rowsep='1'>
+        <colspec colname="section" />
+        <colspec colname="profile" />
+
+        <thead>
+          <row>
+            <entry>Section</entry>
+            <entry>Profile</entry>
+          </row>
+        </thead>
+
+        <tbody>
+          <row>
+            <entry><literal>.linux</literal></entry>
+            <entry morerows="3" valign="middle">Base profile</entry>
+          </row>
+          <row>
+            <entry><literal>.osrel</literal></entry>
+          </row>
+          <row>
+            <entry><literal>.cmdline</literal></entry>
+          </row>
+          <row>
+            <entry><literal>.initrd</literal></entry>
+          </row>
+          <row>
+            <entry><literal>.profile</literal></entry>
+            <entry>Profile @0</entry>
+          </row>
+          <row>
+            <entry><literal>.profile</literal></entry>
+            <entry morerows="1" valign="middle">Profile @1</entry>
+          </row>
+          <row>
+            <entry><literal>.cmdline</literal></entry>
+          </row>
+          <row>
+            <entry><literal>.profile</literal></entry>
+            <entry morerows="1" valign="middle">Profile @2</entry>
+          </row>
+          <row>
+            <entry><literal>.cmdline</literal></entry>
+          </row>
+        </tbody>
+      </tgroup>
+    </table>
+
+    <para>The section list above would define three profiles. The first four sections make up the base
+    profile. A <literal>.profile</literal> section then introduces profile @0. It doesn't override any
+    sections (or add any) from the base section, hence it is immediately followed by another
+    <literal>.profile</literal> section that then introduces section @1. This profile overrides the kernel
+    command line. Finally, the last two sections define section @2, again overriding the command line. (Note
+    that in this example the first <literal>.cmdline</literal> could also moved behind the first
+    <literal>.profile</literal> with equivalent effect. To keep things nicely extensible, it's probably a
+    good idea to keep the generic command line in the base section instead of profile 0, in case later added
+    profiles might want to reuse it.)</para>
+
+    <para>The profile to boot may be controlled via the UKI's own command line: if the first argument starts
+    with <literal>@</literal>, followed by a positive integer number in decimal, it selects the profile to
+    boot into. If the first argument is not specified like that, the UKI will automatically boot into profile
+    0.</para>
+
+    <para>A <literal>.profile</literal> section may contain meta-information about the profile. It follows a
+    similar format as <literal>.osrel</literal> (i.e. an environment-variable-assignment-block-like list of
+    newline separated strings). Currently two fields are defined: <literal>ID=</literal> is supposed to carry
+    a short identifying string that identifies the profile
+    (e.g. <literal>ID=factory-reset</literal>). <literal>TITLE=</literal> should contain a human readable
+    string that may appear in the boot menu entry for this profile (e.g. <literal>TITLE='Factory Reset this
+    Device'</literal>).</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
   <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>
+    core kernel, the embedded initrd and kernel command line (see above for a full list), including all UKI
+    profiles.</para>

 
     <para>Also note that the Linux kernel will measure all initrds it receives into TPM PCR 9. This means
 
     <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 (of the selected UKI profile) will possibly 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>
 
     <table>
       <title>OS Resource PCR Summary</title>


@@ -246,6 +394,11 @@
             <entry>4 + 9 + 11</entry>
           </row>
 
             <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>
             <entry>Default kernel command line (embedded in unified PE binary)</entry>
             <entry>4 + 11</entry>


@@ -280,6 +433,16 @@
             <entry>System Extensions (synthesized initrd from companion files)</entry>
             <entry>9 + 13</entry>
           </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>
+
+          <row>
+            <entry>Selected profile unless zero</entry>
+            <entry>12</entry>
+          </row>

         </tbody>
       </tgroup>
     </table>
         </tbody>
       </tgroup>
     </table>


@@ -296,12 +459,16 @@
       <varlistentry>
         <term><varname>LoaderDevicePartUUID</varname></term>
 
       <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>
+        <listitem><para>Contains the partition UUID of the partition the boot loader has been started from on
+        the current boot (usually a EFI System Partition). If already set by the boot loader, this will
+        remain untouched by <command>systemd-stub</command>. If not set yet, this will be set to the
+        partition UUID of the partition the unified kernel is started from, in order to support systems that
+        directly boot into a unified kernel image, bypassing any boot loader.
+        <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>
 
         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>
+        <xi:include href="version-info.xml" xpointer="v224"/></listitem>

       </varlistentry>
 
       <varlistentry>
       </varlistentry>
 
       <varlistentry>


@@ -318,12 +485,27 @@
       <varlistentry>
         <term><varname>LoaderImageIdentifier</varname></term>
 
       <varlistentry>
         <term><varname>LoaderImageIdentifier</varname></term>
 

-        <listitem><para>The path of EFI executable, relative to the EFI System Partition's root
-        directory. Use
+        <listitem><para>The file system path to the EFI executable of the boot loader for the current boot,
+        relative to the partition's root directory (i.e. relative to the partition indicated by
+        <varname>LoaderDevicePartUUID</varname>, see above). If not set yet, this will be set to the file
+        system path of the EFI executable of the booted unified kernel, in order to support systems that
+        directly boot into a unified kernel image, bypassing any boot loader.  Use

         <citerefentry><refentrytitle>bootctl</refentrytitle><manvolnum>1</manvolnum></citerefentry> to view
         this data.</para>
 
         <citerefentry><refentrytitle>bootctl</refentrytitle><manvolnum>1</manvolnum></citerefentry> to view
         this data.</para>
 

-        <xi:include href="version-info.xml" xpointer="v250"/></listitem>
+        <xi:include href="version-info.xml" xpointer="v237"/></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>StubDevicePartUUID</varname></term>
+        <term><varname>StubImageIdentifier</varname></term>
+
+        <listitem><para>Similar to <varname>LoaderDevicePartUUID</varname> and
+        <varname>StubImageIdentifier</varname>, but indicates the location of the unified kernel image EFI
+        binary rather than the location of the boot loader binary, regardless if booted via a boot loader
+        or not.</para>
+
+        <xi:include href="version-info.xml" xpointer="v257"/></listitem>

       </varlistentry>
 
       <varlistentry>
       </varlistentry>
 
       <varlistentry>


@@ -360,13 +542,34 @@
       <varlistentry>
         <term><varname>StubPcrInitRDSysExts</varname></term>
 
       <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>
         <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>
+
+      <varlistentry>
+        <term><varname>StubProfile</varname></term>
+
+        <listitem><para>The numeric index of the selected profile, without the <literal>@</literal>,
+        formatted as decimal string. Set both on single-profile and multi-profile UKIs. (In the former case
+        this variable will be set to <literal>0</literal> unconditionally.)</para>
+
+        <xi:include href="version-info.xml" xpointer="v257"/></listitem>
+      </varlistentry>

     </variablelist>
 
     <para>Note that some of the variables above may also be set by the boot loader. The stub will only set
     </variablelist>
 
     <para>Note that some of the variables above may also be set by the boot loader. The stub will only set


@@ -384,7 +587,8 @@
       <varlistentry>
         <term><filename>/</filename></term>
 
       <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>
 
         <xi:include href="version-info.xml" xpointer="v252"/></listitem>
       </varlistentry>


@@ -401,8 +605,8 @@
 
       <varlistentry>
         <term><filename>/.extra/global_credentials/*.cred</filename></term>
 
       <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>
 
         <filename>/.extra/global_credentials/</filename> directory in the initrd execution
         environment.</para>
 


@@ -410,32 +614,49 @@
       </varlistentry>
 
       <varlistentry>
       </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>
 
         <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
       <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>
 
       <varlistentry>
 
         <xi:include href="version-info.xml" xpointer="v252"/></listitem>
       </varlistentry>
 
       <varlistentry>

-        <term><filename>/.extra/tpm2-pcr-pkey.pem</filename></term>
+        <term><filename>/.extra/tpm2-pcr-public-key.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>
         <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>

+
+      <varlistentry>
+        <term><filename>/.extra/profile</filename></term>
+        <term><filename>/.extra/os-release</filename></term>
+        <listitem><para>The contents of the <literal>.profile</literal> and <literal>.osrel</literal>
+        sections of the selected profile, if any.</para>
+
+        <xi:include href="version-info.xml" xpointer="v257"/></listitem>
+      </varlistentry>

     </variablelist>
 
     <para>Note that all these files are located in the <literal>tmpfs</literal> file system the kernel sets
     </variablelist>
 
     <para>Note that all these files are located in the <literal>tmpfs</literal> file system the kernel sets


@@ -450,7 +671,8 @@
     <title>SMBIOS Type 11 Strings</title>
 
     <para><command>systemd-stub</command> can be configured using SMBIOS Type 11 strings. Applicable strings
     <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>
 
     <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>
 


@@ -474,15 +696,16 @@
 
   <refsect1>
     <title>See Also</title>
 
   <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>
-    </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>
   </refsect1>
 </refentry>