diff options
Diffstat (limited to 'man')
| -rw-r--r-- | man/systemd-measure.xml | 59 | ||||
| -rw-r--r-- | man/systemd-stub.xml | 115 |
2 files changed, 148 insertions, 26 deletions
diff --git a/man/systemd-measure.xml b/man/systemd-measure.xml index 0fc0d0e87d..69ac348184 100644 --- a/man/systemd-measure.xml +++ b/man/systemd-measure.xml @@ -37,12 +37,12 @@ <citerefentry><refentrytitle>systemd-stub</refentrytitle><manvolnum>7</manvolnum></citerefentry> is booted up. It accepts paths to the ELF kernel image file, initial ram disk image file, devicetree file, kernel command line file, - <citerefentry><refentrytitle>os-release</refentrytitle><manvolnum>5</manvolnum></citerefentry> file, and - boot splash file that make up the unified kernel image, and determines the PCR values expected to be in - place after booting the image. Calculation starts with a zero-initialized PCR 11, and is executed in a - fashion compatible with what <filename>systemd-stub</filename> does at boot. The result may optionally be - signed cryptographically, to allow TPM2 policies that can only be unlocked if a certain set of kernels is - booted, for which such a PCR signature can be provided.</para> + <citerefentry><refentrytitle>os-release</refentrytitle><manvolnum>5</manvolnum></citerefentry> file, boot + splash file, and TPM2 PCR PEM public key file that make up the unified kernel image, and determines the + PCR values expected to be in place after booting the image. Calculation starts with a zero-initialized + PCR 11, and is executed in a fashion compatible with what <filename>systemd-stub</filename> does at + boot. The result may optionally be signed cryptographically, to allow TPM2 policies that can only be + unlocked if a certain set of kernels is booted, for which such a PCR signature can be provided.</para> </refsect1> <refsect1> @@ -66,9 +66,9 @@ <listitem><para>Pre-calculate the expected values seen in PCR register 11 after boot-up of a unified kernel image consisting of the components specified with <option>--linux=</option>, <option>--osrel=</option>, <option>--cmdline=</option>, <option>--initrd=</option>, - <option>--splash=</option>, <option>--dtb=</option>, see below. Only <option>--linux=</option> is - mandatory. (Alternatively, specify <option>--current</option> to use the current values of PCR - register 11 instead.)</para></listitem> + <option>--splash=</option>, <option>--dtb=</option>, <option>--pcrpkey=</option> see below. Only + <option>--linux=</option> is mandatory. (Alternatively, specify <option>--current</option> to use the + current values of PCR register 11 instead.)</para></listitem> </varlistentry> <varlistentry> @@ -104,6 +104,7 @@ <term><option>--initrd=PATH</option></term> <term><option>--splash=PATH</option></term> <term><option>--dtb=PATH</option></term> + <term><option>--pcrpkey=PATH</option></term> <listitem><para>When used with the <command>calculate</command> or <command>sign</command> verb, configures the files to read the unified kernel image components from. Each option corresponds with @@ -135,7 +136,14 @@ <term><option>--public-key=PATH</option></term> <listitem><para>These switches take paths to a pair of PEM encoded RSA key files, for use with - the <command>sign</command> command.</para></listitem> + the <command>sign</command> command.</para> + + <para>Note the difference between the <option>--pcrpkey=</option> and <option>--public-key=</option> + switches. The former selects the data to include in the <literal>.pcrpkey</literal> PE section of the + unified kernel image, the latter picks the public key of the key pair used to sign the resulting PCR + 11 values. The former is the key that the booted system will likely use to lock disk and credential + encryption to, the latter is the key used for unlocking such resources again. Hence, typically the + same PEM key should be supplied in both cases.</para></listitem> </varlistentry> <varlistentry> @@ -185,19 +193,11 @@ </example> <example> - <title>Generate a private/public key pair, and a unified kernel image, and a TPM PCR 11 signature for it</title> + <title>Generate a private/public key pair, and a unified kernel image, and a TPM PCR 11 signature for + it, and embed the signature and the public key in the image</title> <programlisting># openssl genpkey -algorithm RSA -pkeyopt rsa_keygen_bits:2048 -out tpm2-pcr-private.pem # openssl rsa -pubout -in tpm2-pcr-private.pem -out tpm2-pcr-public.pem -# objcopy \ - --add-section .linux=vmlinux --change-section-vma .linux=0x2000000 \ - --add-section .osrel=os-release.txt --change-section-vma .osrel=0x20000 \ - --add-section .cmdline=cmdline.txt --change-section-vma .cmdline=0x30000 \ - --add-section .initrd=initrd.cpio --change-section-vma .initrd=0x3000000 \ - --add-section .splash=splash.bmp --change-section-vma .splash=0x100000 \ - --add-section .dtb=devicetree.dtb --change-section-vma .dtb=0x40000 \ - /usr/lib/systemd/boot/efi/linuxx64.efi.stub \ - foo.efi # systemd-measure sign \ --linux=vmlinux \ --osrel=os-release.txt \ @@ -205,10 +205,22 @@ --initrd=initrd.cpio \ --splash=splash.bmp \ --dtb=devicetree.dtb \ + --pcrpkey=tpm2-pcr-public.pem \ --bank=sha1 \ --bank=sha256 \ --private-key=tpm2-pcr-private.pem \ - --public-key=tpm2-pcr-public.pem > tpm2-pcr-signature.json</programlisting> + --public-key=tpm2-pcr-public.pem > tpm2-pcr-signature.json +# objcopy \ + --add-section .linux=vmlinux --change-section-vma .linux=0x2000000 \ + --add-section .osrel=os-release.txt --change-section-vma .osrel=0x20000 \ + --add-section .cmdline=cmdline.txt --change-section-vma .cmdline=0x30000 \ + --add-section .initrd=initrd.cpio --change-section-vma .initrd=0x3000000 \ + --add-section .splash=splash.bmp --change-section-vma .splash=0x100000 \ + --add-section .dtb=devicetree.dtb --change-section-vma .dtb=0x40000 \ + --add-section .pcrsig=tpm2-pcr-signature.json --change-section-vma .splash=0x80000 \ + --add-section .pcrpkey=tpm2-pcr-public.pem --change-section-vma .splash=0x90000 \ + /usr/lib/systemd/boot/efi/linuxx64.efi.stub \ + foo.efi</programlisting> <para>Later on, enroll the signed PCR policy on a LUKS volume:</para> @@ -217,6 +229,11 @@ <para>And then unlock the device with the signature:</para> <programlisting># /usr/lib/systemd/systemd-cryptsetup attach myvolume /dev/sda5 - tpm2-device=auto,tpm2-signature=/path/to/tpm2-pcr-signature.json</programlisting> + + <para>Note that when the generated unified kernel image <filename>foo.efi</filename> is booted the + signature and public key files will be placed at locations <command>systemd-cryptenroll</command> and + <command>systemd-cryptsetup</command> will look for anyway, and thus these paths do not actually need to + be specified.</para> </example> </refsect1> diff --git a/man/systemd-stub.xml b/man/systemd-stub.xml index 1e9bb5d631..2479d9f5fa 100644 --- a/man/systemd-stub.xml +++ b/man/systemd-stub.xml @@ -68,6 +68,14 @@ <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 @@ -81,8 +89,25 @@ DeviceTree in the corresponding EFI configuration table. systemd-stub will ask the firmware via the <literal>EFI_DT_FIXUP_PROTOCOL</literal> for hardware specific fixups to the DeviceTree.</para> - <para>The contents of these six PE sections are measured into TPM PCR 11, that is otherwise not - used. Thus, it can be pre-calculated without too much effort.</para> + <para>The contents of seven of these eight PE sections are measured into TPM PCR 11, that is otherwise + not used. Thus, it can be pre-calculated without too much effort. The <literal>.pcrsig</literal> section + is not included in this PCR measurement, since it's supposed to contain signatures for the expected + results for these measurements, i.e. of the outputs of the measurement operation, and thus cannot also be + input to it.</para> + + <para>When <literal>.pcrsig</literal> and/or <literal>.pcrpkey</literal> are present in a unified kernel + image their contents are passed to the booted kernel in an synthetic initrd cpio archive that places them in the + <filename>/.extra/tpm2-pcr-signature.json</filename> and + <filename>/.extra/tpm2-pcr-public-key.pem</filename> files. Typically, a + <citerefentry><refentrytitle>tmpfiles.d</refentrytitle><manvolnum>5</manvolnum></citerefentry> line then + ensures they are copied into <filename>/run/systemd/tpm2-pcr-signature.json</filename> and + <filename>/run/systemd/tpm2-pcr-public-key.pem</filename> where they remain accessible even after the + system transitions out of the initrd environment into the host file system. Tools such + <citerefentry><refentrytitle>systemd-cryptsetup@.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>, + <citerefentry><refentrytitle>systemd-cryptenroll</refentrytitle><manvolnum>1</manvolnum></citerefentry> + and <citerefentry><refentrytitle>systemd-creds</refentrytitle><manvolnum>1</manvolnum></citerefentry> + will automatically use files present under these paths to unlock protected resources (encrypted storage + or credentials) or bind encryption to booted kernels.</para> </refsect1> <refsect1> @@ -166,12 +191,12 @@ </row> <row> - <entry>Boot splash (embedded in the unified PE binary)</entry> + <entry>Core kernel code (embedded in unified PE binary)</entry> <entry>4 + 11</entry> </row> <row> - <entry>Core kernel code (embedded in unified PE binary)</entry> + <entry>OS release information (embedded in the unified PE binary)</entry> <entry>4 + 11</entry> </row> @@ -191,6 +216,21 @@ </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> @@ -280,6 +320,66 @@ </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 @@ -313,6 +413,10 @@ <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> @@ -325,7 +429,8 @@ <ulink url="https://systemd.io/BOOT_LOADER_SPECIFICATION">Boot Loader Specification</ulink>, <ulink url="https://systemd.io/BOOT_LOADER_INTERFACE">Boot Loader Interface</ulink>, <citerefentry project='man-pages'><refentrytitle>objcopy</refentrytitle><manvolnum>1</manvolnum></citerefentry>, - <citerefentry project='archlinux'><refentrytitle>sbsign</refentrytitle><manvolnum>1</manvolnum></citerefentry> + <citerefentry project='archlinux'><refentrytitle>sbsign</refentrytitle><manvolnum>1</manvolnum></citerefentry>, + <citerefentry><refentrytitle>systemd-measure</refentrytitle><manvolnum>1</manvolnum></citerefentry> </para> </refsect1> </refentry> |