Adding upstream version 252.22.upstream/252.22upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 440 insertions, 0 deletions

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+<?xml version='1.0'?> <!--*-nxml-*-->
+<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
+  "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
+<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
+
+<refentry id="systemd-stub" conditional='HAVE_GNU_EFI'
+    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><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/*.cred</filename></para>
+    <para><filename><replaceable>ESP</replaceable>/.../<replaceable>foo</replaceable>.efi.extra.d/*.raw</filename></para>
+    <para><filename><replaceable>ESP</replaceable>/loader/credentials/*.cred</filename></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>
+      <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>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>The initrd will be loaded from the <literal>.initrd</literal> PE section.
+      </para></listitem>
+
+      <listitem><para>A compiled binary DeviceTree will be looked for in the <literal>.dtb</literal> PE
+      section.</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 boot splash (in Windows <filename>.BMP</filename> format) to show on screen before
+      invoking the kernel will be looked for in the <literal>.splash</literal> PE section.</para></listitem>
+
+      <listitem><para>A set of cryptographic signatures for expected TPM2 PCR values when this kernel is
+      booted, in JSON format, in the <literal>.pcrsig</literal> section. This is useful for implementing TPM2
+      policies that bind disk encryption and similar to kernels that are signed by a specific
+      key.</para></listitem>
+
+      <listitem><para>A public key in PEM format matching this TPM2 PCR signature data in the
+      <literal>.pcrpkey</literal> section.</para></listitem>
+    </itemizedlist>
+
+    <para>If UEFI SecureBoot is enabled and the <literal>.cmdline</literal> section is present in the executed
+    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
+    <filename>/.extra/tpm2-pcr-public-key.pem</filename> files. Typically, a
+    <citerefentry><refentrytitle>tmpfiles.d</refentrytitle><manvolnum>5</manvolnum></citerefentry> line then
+    ensures they are copied into <filename>/run/systemd/tpm2-pcr-signature.json</filename> and
+    <filename>/run/systemd/tpm2-pcr-public-key.pem</filename> where they remain accessible even after the
+    system transitions out of the initrd environment into the host file system. Tools such
+    <citerefentry><refentrytitle>systemd-cryptsetup@.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
+    <citerefentry><refentrytitle>systemd-cryptenroll</refentrytitle><manvolnum>1</manvolnum></citerefentry>
+    and <citerefentry><refentrytitle>systemd-creds</refentrytitle><manvolnum>1</manvolnum></citerefentry>
+    will automatically use files present under these paths to unlock protected resources (encrypted storage
+    or credentials) or bind encryption to booted kernels.</para>
+  </refsect1>
+
+  <refsect1>
+    <title>Companion Files</title>
+
+    <para>The <command>systemd-stub</command> UEFI boot stub automatically collects two 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. 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/*.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>
+
+      <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>
+    </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 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>
+
+    <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>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>
+        </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></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></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></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></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></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></listitem>
+      </varlistentry>
+
+      <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.
+        <literal>13</literal>). This variable is set if a measurement was successfully completed, and remains
+        unset otherwise.</para></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></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><filename>/.extra/credentials/*.cred</filename></term>
+        <listitem><para>Credential files (suffix <literal>.cred</literal>) that are placed next to the
+        unified kernel image (as described above) are copied into the
+        <filename>/.extra/credentials/</filename> directory in the initrd execution
+        environment.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><filename>/.extra/global_credentials/*.cred</filename></term>
+        <listitem><para>Similar, credential files in the <filename>/loader/credentials/</filename> directory
+        in the file system the unified kernel image is placed in are copied into the
+        <filename>/.extra/global_credentials/</filename> directory in the initrd execution
+        environment.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><filename>/.extra/sysext/*.raw</filename></term>
+        <listitem><para>System extension image files (suffix <literal>.raw</literal>) that are placed next to
+        the unified kernel image (as described above) are copied into the
+        <filename>/.extra/sysext/</filename> directory in the initrd execution environment.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><filename>/.extra/tpm2-pcr-signature.json</filename></term>
+        <listitem><para>The TPM2 PCR signature JSON object included in the <literal>.pcrsig</literal> PE
+        section of the unified kernel image is copied into the
+        <filename>/.extra/tpm2-pcr-signature.json</filename> file in the initrd execution
+        environment.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><filename>/.extra/tpm2-pcr-pkey.pem</filename></term>
+        <listitem><para>The PEM public key included in the <literal>.pcrpkey</literal> PE section of the
+        unified kernel image is copied into the <filename>/.extra/tpm2-pcr-public-key.pem</filename> file in
+        the initrd execution environment.</para></listitem>
+      </varlistentry>
+    </variablelist>
+
+    <para>Note that all these files are located in the <literal>tmpfs</literal> file system the kernel sets
+    up for the initrd file hierarchy and are thus lost when the system transitions from the initrd execution
+    environment into the host file system. If these resources shall be kept around over this transition they
+    need to be copied to a place that survives the transition first, for example via a suitable
+    <citerefentry><refentrytitle>tmpfiles.d</refentrytitle><manvolnum>5</manvolnum></citerefentry> line. By
+    default, this is done for the TPM2 PCR signature and public key files.</para>
+  </refsect1>
+
+  <refsect1>
+    <title>Assembling Kernel Images</title>
+
+    <para>In order to assemble an UEFI PE kernel image from various components as described above, use an
+    <citerefentry project='man-pages'><refentrytitle>objcopy</refentrytitle><manvolnum>1</manvolnum></citerefentry> command line
+    like this:</para>
+
+    <programlisting>objcopy \
+    --add-section .osrel=os-release --change-section-vma .osrel=0x20000 \
+    --add-section .cmdline=cmdline.txt --change-section-vma .cmdline=0x30000 \
+    --add-section .dtb=devicetree.dtb --change-section-vma .dtb=0x40000 \
+    --add-section .splash=splash.bmp --change-section-vma .splash=0x100000 \
+    --add-section .linux=vmlinux --change-section-vma .linux=0x2000000 \
+    --add-section .initrd=initrd.cpio --change-section-vma .initrd=0x3000000 \
+    /usr/lib/systemd/boot/efi/linuxx64.efi.stub \
+    foo-unsigned.efi</programlisting>
+
+    <para>Note that these PE section offsets are example values and a properly assembled image must not
+    contain any overlapping sections (this includes already existing sections inside the stub before
+    assembly) or boot may fail.</para>
+
+    <para>This generates one PE executable file <filename>foo-unsigned.efi</filename> from the six individual
+    files for OS release information, kernel command line, boot splash image, kernel image, main initrd and
+    UEFI boot stub.</para>
+
+    <para>To then sign the resulting image for UEFI SecureBoot use an
+    <citerefentry project='archlinux'><refentrytitle>sbsign</refentrytitle><manvolnum>1</manvolnum></citerefentry> command like
+    the following:</para>
+
+    <programlisting>sbsign \
+    --key mykey.pem \
+    --cert mykey.crt \
+    --output foo.efi \
+    foo-unsigned.efi</programlisting>
+
+    <para>This expects a pair of X.509 private key and certificate as parameters and then signs the UEFI PE
+    executable we generated above for UEFI SecureBoot and generates a signed UEFI PE executable as
+    result.</para>
+
+    <para>See
+    <citerefentry><refentrytitle>systemd-measure</refentrytitle><manvolnum>1</manvolnum></citerefentry> for
+    an example involving the <literal>.pcrsig</literal> and <literal>.pcrpkey</literal> sections.</para>
+  </refsect1>
+
+  <refsect1>
+    <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://systemd.io/BOOT_LOADER_SPECIFICATION">Boot Loader Specification</ulink>,
+      <ulink url="https://systemd.io/BOOT_LOADER_INTERFACE">Boot Loader Interface</ulink>,
+      <citerefentry project='man-pages'><refentrytitle>objcopy</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
+      <citerefentry project='archlinux'><refentrytitle>sbsign</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>systemd-measure</refentrytitle><manvolnum>1</manvolnum></citerefentry>
+    </para>
+  </refsect1>
+</refentry>