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1 | <?xml version="1.0"?> |
2 | <!--*-nxml-*--> | |
3 | <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" | |
4 | "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> | |
5 | <!-- SPDX-License-Identifier: LGPL-2.1-or-later --> | |
6 | <refentry id="systemd-measure" xmlns:xi="http://www.w3.org/2001/XInclude" conditional='HAVE_GNU_EFI'> | |
7 | ||
8 | <refentryinfo> | |
9 | <title>systemd-measure</title> | |
10 | <productname>systemd</productname> | |
11 | </refentryinfo> | |
12 | ||
13 | <refmeta> | |
14 | <refentrytitle>systemd-measure</refentrytitle> | |
15 | <manvolnum>1</manvolnum> | |
16 | </refmeta> | |
17 | ||
18 | <refnamediv> | |
19 | <refname>systemd-measure</refname> | |
cdaaa62c | 20 | <refpurpose>Pre-calculate and sign expected TPM2 PCR values for booted unified kernel images</refpurpose> |
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21 | </refnamediv> |
22 | ||
23 | <refsynopsisdiv> | |
24 | <cmdsynopsis> | |
25 | <command>/usr/lib/systemd/systemd-measure <arg choice="opt" rep="repeat">OPTIONS</arg></command> | |
26 | </cmdsynopsis> | |
27 | </refsynopsisdiv> | |
28 | ||
29 | <refsect1> | |
30 | <title>Description</title> | |
31 | ||
32 | <para>Note: this command is experimental for now. While it is likely to become a regular component of | |
33 | systemd, it might still change in behaviour and interface.</para> | |
34 | ||
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35 | <para><command>systemd-measure</command> is a tool that may be used to pre-calculate and sign the |
36 | expected TPM2 PCR 11 values that should be seen when a unified Linux kernel image based on | |
ca1092dc | 37 | <citerefentry><refentrytitle>systemd-stub</refentrytitle><manvolnum>7</manvolnum></citerefentry> is |
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38 | booted up. It accepts paths to the ELF kernel image file, initrd image file, devicetree file, kernel |
39 | command line file, | |
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40 | <citerefentry><refentrytitle>os-release</refentrytitle><manvolnum>5</manvolnum></citerefentry> file, boot |
41 | splash file, and TPM2 PCR PEM public key file that make up the unified kernel image, and determines the | |
42 | PCR values expected to be in place after booting the image. Calculation starts with a zero-initialized | |
43 | PCR 11, and is executed in a fashion compatible with what <filename>systemd-stub</filename> does at | |
44 | boot. The result may optionally be signed cryptographically, to allow TPM2 policies that can only be | |
45 | unlocked if a certain set of kernels is booted, for which such a PCR signature can be provided.</para> | |
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46 | </refsect1> |
47 | ||
48 | <refsect1> | |
49 | <title>Commands</title> | |
50 | ||
51 | <para>The following commands are understood:</para> | |
52 | ||
53 | <variablelist> | |
54 | <varlistentry> | |
55 | <term><command>status</command></term> | |
56 | ||
57 | <listitem><para>This is the default command if none is specified. This queries the local system's | |
58 | TPM2 PCR 11+12+13 values and displays them. The data is written in a similar format as the | |
59 | <command>calculate</command> command below, and may be used to quickly compare expectation with | |
60 | reality.</para></listitem> | |
61 | </varlistentry> | |
62 | ||
63 | <varlistentry> | |
64 | <term><command>calculate</command></term> | |
65 | ||
cdaaa62c | 66 | <listitem><para>Pre-calculate the expected values seen in PCR register 11 after boot-up of a unified |
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67 | kernel image consisting of the components specified with <option>--linux=</option>, |
68 | <option>--osrel=</option>, <option>--cmdline=</option>, <option>--initrd=</option>, | |
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69 | <option>--splash=</option>, <option>--dtb=</option>, <option>--pcrpkey=</option> see below. Only |
70 | <option>--linux=</option> is mandatory. (Alternatively, specify <option>--current</option> to use the | |
71 | current values of PCR register 11 instead.)</para></listitem> | |
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72 | </varlistentry> |
73 | ||
74 | <varlistentry> | |
75 | <term><command>sign</command></term> | |
76 | ||
77 | <listitem><para>As with the <command>calculate</command> command, pre-calculate the expected value | |
78 | seen in TPM2 PCR register 11 after boot-up of a unified kernel image. Then, cryptographically sign | |
79 | the resulting values with the private/public key pair (RSA) configured via | |
80 | <option>--private-key=</option> and <option>--public-key=</option>. This will write a JSON object to | |
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81 | standard output that contains signatures for all specified PCR banks (see the |
82 | <option>--pcr-bank=</option> option below), which may be used to unlock encrypted credentials (see | |
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83 | <citerefentry><refentrytitle>systemd-creds</refentrytitle><manvolnum>1</manvolnum></citerefentry>) or |
84 | LUKS volumes (see | |
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85 | <citerefentry><refentrytitle>systemd-cryptsetup@.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>). |
86 | This allows binding secrets to a set of kernels for which such PCR 11 signatures can be | |
87 | provided.</para> | |
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88 | |
89 | <para>Note that a TPM2 device must be available for this signing to take place, even though the | |
90 | result is not tied to any TPM2 device or its state.</para></listitem> | |
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91 | </varlistentry> |
92 | </variablelist> | |
93 | </refsect1> | |
94 | ||
95 | <refsect1> | |
96 | <title>Options</title> | |
97 | ||
98 | <para>The following options are understood:</para> | |
99 | ||
100 | <variablelist> | |
101 | <varlistentry> | |
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102 | <term><option>--linux=<replaceable>PATH</replaceable></option></term> |
103 | <term><option>--osrel=<replaceable>PATH</replaceable></option></term> | |
104 | <term><option>--cmdline=<replaceable>PATH</replaceable></option></term> | |
105 | <term><option>--initrd=<replaceable>PATH</replaceable></option></term> | |
106 | <term><option>--splash=<replaceable>PATH</replaceable></option></term> | |
107 | <term><option>--dtb=<replaceable>PATH</replaceable></option></term> | |
108 | <term><option>--pcrpkey=<replaceable>PATH</replaceable></option></term> | |
ca1092dc | 109 | |
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110 | <listitem><para>When used with the <command>calculate</command> or <command>sign</command> verb, |
111 | configures the files to read the unified kernel image components from. Each option corresponds with | |
112 | the equally named section in the unified kernel PE file. The <option>--linux=</option> switch expects | |
113 | the path to the ELF kernel file that the unified PE kernel will wrap. All switches except | |
114 | <option>--linux=</option> are optional. Each option may be used at most once.</para></listitem> | |
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115 | </varlistentry> |
116 | ||
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117 | <varlistentry> |
118 | <term><option>--current</option></term> | |
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119 | <listitem><para>When used with the <command>calculate</command> or <command>sign</command> verb, |
120 | takes the PCR 11 values currently in effect for the system (which should typically reflect the hashes | |
121 | of the currently booted kernel). This can be used in place of <option>--linux=</option> and the other | |
122 | switches listed above.</para></listitem> | |
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123 | </varlistentry> |
124 | ||
ca1092dc | 125 | <varlistentry> |
8b9f0921 | 126 | <term><option>--bank=<replaceable>DIGEST</replaceable></option></term> |
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127 | |
128 | <listitem><para>Controls the PCR banks to pre-calculate the PCR values for – in case | |
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129 | <command>calculate</command> or <command>sign</command> is invoked –, or the banks to show in the |
130 | <command>status</command> output. May be used more then once to specify multiple banks. If not | |
131 | specified, defaults to the four banks <literal>sha1</literal>, <literal>sha256</literal>, | |
132 | <literal>sha384</literal>, <literal>sha512</literal>.</para></listitem> | |
133 | </varlistentry> | |
134 | ||
135 | <varlistentry> | |
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136 | <term><option>--private-key=<replaceable>PATH</replaceable></option></term> |
137 | <term><option>--public-key=<replaceable>PATH</replaceable></option></term> | |
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138 | |
139 | <listitem><para>These switches take paths to a pair of PEM encoded RSA key files, for use with | |
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140 | the <command>sign</command> command.</para> |
141 | ||
142 | <para>Note the difference between the <option>--pcrpkey=</option> and <option>--public-key=</option> | |
143 | switches. The former selects the data to include in the <literal>.pcrpkey</literal> PE section of the | |
144 | unified kernel image, the latter picks the public key of the key pair used to sign the resulting PCR | |
145 | 11 values. The former is the key that the booted system will likely use to lock disk and credential | |
146 | encryption to, the latter is the key used for unlocking such resources again. Hence, typically the | |
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147 | same PEM key should be supplied in both cases.</para> |
148 | ||
149 | <para>If the <option>--public-key=</option> is not specified but <option>--private-key=</option> is | |
150 | specified the public key is automatically derived from the private key.</para></listitem> | |
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151 | </varlistentry> |
152 | ||
153 | <varlistentry> | |
154 | <term><option>--tpm2-device=</option><replaceable>PATH</replaceable></term> | |
155 | ||
156 | <listitem><para>Controls which TPM2 device to use. Expects a device node path referring to the TPM2 | |
157 | chip (e.g. <filename>/dev/tpmrm0</filename>). Alternatively the special value <literal>auto</literal> | |
158 | may be specified, in order to automatically determine the device node of a suitable TPM2 device (of | |
159 | which there must be exactly one). The special value <literal>list</literal> may be used to enumerate | |
160 | all suitable TPM2 devices currently discovered.</para></listitem> | |
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161 | </varlistentry> |
162 | ||
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163 | <varlistentry> |
164 | <term><option>--phase=</option><replaceable>PHASE</replaceable></term> | |
165 | ||
0923b425 | 166 | <listitem><para>Controls which boot phases to calculate expected PCR 11 values for. This takes a |
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167 | series of colon-separated strings that encode boot "paths" for entering a specific phase of the boot |
168 | process. Each of the specified strings is measured by the | |
169 | <filename>systemd-pcrphase-initrd.service</filename> and | |
170 | <citerefentry><refentrytitle>systemd-pcrphase.service</refentrytitle><manvolnum>8</manvolnum></citerefentry> | |
171 | into PCR 11 during different milestones of the boot process. This switch may be specified multiple | |
172 | times to calculate PCR values for multiple boot phases at once. If not used defaults to | |
173 | <literal>enter-initrd</literal>, <literal>enter-initrd:leave-initrd</literal>, | |
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174 | <literal>enter-initrd:leave-initrd:sysinit</literal>, |
175 | <literal>enter-initrd:leave-initrd:sysinit:ready</literal>, i.e. calculates expected PCR values for | |
176 | the boot phase in the initrd, during early boot, during later boot, and during system runtime, but | |
177 | excluding the phases before the initrd or when shutting down. This setting is honoured both by | |
178 | <command>calculate</command> and <command>sign</command>. When used with the latter it's particularly | |
179 | useful for generating PCR signatures that can only be used for unlocking resources during specific | |
180 | parts of the boot process.</para> | |
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181 | |
182 | <para>For further details about PCR boot phases, see | |
183 | <citerefentry><refentrytitle>systemd-pcrphase.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para></listitem> | |
184 | </varlistentry> | |
185 | ||
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186 | <varlistentry> |
187 | <term><option>--append=</option><replaceable>PATH</replaceable></term> | |
188 | ||
189 | <listitem><para>When generating a PCR JSON signature (via the <command>sign</command> command), | |
190 | combine it with a previously generated PCR JSON signature, and output it as one. The specified path | |
191 | must refer to a regular file that contains a valid JSON PCR signature object. The specified file is | |
192 | not modified. It will be read first, then the newly generated signature appended to it, and the | |
193 | resulting object is written to standard output. Use this to generate a single JSON object consisting | |
194 | from signatures made with a number of signing keys (for example, to have one key per boot phase). The | |
195 | command will suppress duplicates: if a specific signature is already included in a JSON signature | |
196 | object it is not added a second time.</para></listitem> | |
197 | </varlistentry> | |
198 | ||
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199 | <xi:include href="standard-options.xml" xpointer="json" /> |
200 | <xi:include href="standard-options.xml" xpointer="no-pager" /> | |
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201 | <xi:include href="standard-options.xml" xpointer="help" /> |
202 | <xi:include href="standard-options.xml" xpointer="version" /> | |
203 | </variablelist> | |
204 | </refsect1> | |
205 | ||
206 | <refsect1> | |
207 | <title>Examples</title> | |
208 | ||
209 | <example> | |
210 | <title>Generate a unified kernel image, and calculate the expected TPM PCR 11 value</title> | |
211 | ||
212 | <programlisting># objcopy \ | |
213 | --add-section .linux=vmlinux --change-section-vma .linux=0x2000000 \ | |
214 | --add-section .osrel=os-release.txt --change-section-vma .osrel=0x20000 \ | |
215 | --add-section .cmdline=cmdline.txt --change-section-vma .cmdline=0x30000 \ | |
216 | --add-section .initrd=initrd.cpio --change-section-vma .initrd=0x3000000 \ | |
217 | --add-section .splash=splash.bmp --change-section-vma .splash=0x100000 \ | |
218 | --add-section .dtb=devicetree.dtb --change-section-vma .dtb=0x40000 \ | |
219 | /usr/lib/systemd/boot/efi/linuxx64.efi.stub \ | |
220 | foo.efi | |
221 | # systemd-measure calculate \ | |
222 | --linux=vmlinux \ | |
cdaaa62c | 223 | --osrel=os-release.txt \ |
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224 | --cmdline=cmdline.txt \ |
225 | --initrd=initrd.cpio \ | |
226 | --splash=splash.bmp \ | |
227 | --dtb=devicetree.dtb | |
228 | 11:sha1=d775a7b4482450ac77e03ee19bda90bd792d6ec7 | |
229 | 11:sha256=bc6170f9ce28eb051ab465cd62be8cf63985276766cf9faf527ffefb66f45651 | |
230 | 11:sha384=1cf67dff4757e61e5a73d2a21a6694d668629bbc3761747d493f7f49ad720be02fd07263e1f93061243aec599d1ee4b4 | |
231 | 11:sha512=8e79acd3ddbbc8282e98091849c3530f996303c8ac8e87a3b2378b71c8b3a6e86d5c4f41ecea9e1517090c3e8ec0c714821032038f525f744960bcd082d937da | |
232 | </programlisting> | |
233 | </example> | |
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234 | |
235 | <example> | |
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236 | <title>Generate a private/public key pair, and a unified kernel image, and a TPM PCR 11 signature for |
237 | it, and embed the signature and the public key in the image</title> | |
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238 | |
239 | <programlisting># openssl genpkey -algorithm RSA -pkeyopt rsa_keygen_bits:2048 -out tpm2-pcr-private.pem | |
240 | # openssl rsa -pubout -in tpm2-pcr-private.pem -out tpm2-pcr-public.pem | |
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241 | # systemd-measure sign \ |
242 | --linux=vmlinux \ | |
243 | --osrel=os-release.txt \ | |
244 | --cmdline=cmdline.txt \ | |
245 | --initrd=initrd.cpio \ | |
246 | --splash=splash.bmp \ | |
247 | --dtb=devicetree.dtb \ | |
2deca517 | 248 | --pcrpkey=tpm2-pcr-public.pem \ |
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249 | --bank=sha1 \ |
250 | --bank=sha256 \ | |
251 | --private-key=tpm2-pcr-private.pem \ | |
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252 | --public-key=tpm2-pcr-public.pem > tpm2-pcr-signature.json |
253 | # objcopy \ | |
254 | --add-section .linux=vmlinux --change-section-vma .linux=0x2000000 \ | |
255 | --add-section .osrel=os-release.txt --change-section-vma .osrel=0x20000 \ | |
256 | --add-section .cmdline=cmdline.txt --change-section-vma .cmdline=0x30000 \ | |
257 | --add-section .initrd=initrd.cpio --change-section-vma .initrd=0x3000000 \ | |
258 | --add-section .splash=splash.bmp --change-section-vma .splash=0x100000 \ | |
259 | --add-section .dtb=devicetree.dtb --change-section-vma .dtb=0x40000 \ | |
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260 | --add-section .pcrsig=tpm2-pcr-signature.json --change-section-vma .pcrsig=0x80000 \ |
261 | --add-section .pcrpkey=tpm2-pcr-public.pem --change-section-vma .pcrpkey=0x90000 \ | |
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262 | /usr/lib/systemd/boot/efi/linuxx64.efi.stub \ |
263 | foo.efi</programlisting> | |
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264 | |
265 | <para>Later on, enroll the signed PCR policy on a LUKS volume:</para> | |
266 | ||
267 | <programlisting># systemd-cryptenroll --tpm2-device=auto --tpm2-public-key=tpm2-pcr-public.pem --tpm2-signature=tpm2-pcr-signature.json /dev/sda5</programlisting> | |
268 | ||
269 | <para>And then unlock the device with the signature:</para> | |
270 | ||
271 | <programlisting># /usr/lib/systemd/systemd-cryptsetup attach myvolume /dev/sda5 - tpm2-device=auto,tpm2-signature=/path/to/tpm2-pcr-signature.json</programlisting> | |
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272 | |
273 | <para>Note that when the generated unified kernel image <filename>foo.efi</filename> is booted the | |
274 | signature and public key files will be placed at locations <command>systemd-cryptenroll</command> and | |
275 | <command>systemd-cryptsetup</command> will look for anyway, and thus these paths do not actually need to | |
276 | be specified.</para> | |
cdaaa62c | 277 | </example> |
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278 | |
279 | <example> | |
280 | <title>Introduce a second public key, signing the same kernel PCR measurements, but only for the initrd boot phase</title> | |
281 | ||
282 | <para>This example extends the previous one, but we now introduce a second signing key that is only | |
283 | used to sign PCR policies restricted to the initrd boot phase. This can be used to lock down root | |
284 | volumes in a way that they can only be unlocked before the transition to the host system. Thus we have | |
285 | two classes of secrets or credentials: one that can be unlocked during the entire runtime, and the | |
286 | other that can only be used in the initrd.</para> | |
287 | ||
288 | <programlisting># openssl genpkey -algorithm RSA -pkeyopt rsa_keygen_bits:2048 -out tpm2-pcr-private.pem | |
289 | # openssl rsa -pubout -in tpm2-pcr-private.pem -out tpm2-pcr-public.pem | |
290 | # systemd-measure sign \ | |
291 | --linux=vmlinux \ | |
292 | --osrel=os-release.txt \ | |
293 | --cmdline=cmdline.txt \ | |
294 | --initrd=initrd.cpio \ | |
295 | --splash=splash.bmp \ | |
296 | --dtb=devicetree.dtb \ | |
297 | --pcrpkey=tpm2-pcr-public.pem \ | |
298 | --bank=sha1 \ | |
299 | --bank=sha256 \ | |
300 | --private-key=tpm2-pcr-private.pem \ | |
301 | --public-key=tpm2-pcr-public.pem >tpm2-pcr-signature.json.tmp | |
302 | # openssl genpkey -algorithm RSA -pkeyopt rsa_keygen_bits:2048 -out tpm2-pcr-initrd-private.pem | |
303 | # openssl rsa -pubout -in tpm2-pcr-initrd-private.pem -out tpm2-pcr-initrd-public.pem | |
304 | # systemd-measure sign \ | |
305 | --linux=vmlinux \ | |
306 | --osrel=os-release.txt \ | |
307 | --cmdline=cmdline.txt \ | |
308 | --initrd=initrd.cpio \ | |
309 | --splash=splash.bmp \ | |
310 | --dtb=devicetree.dtb \ | |
311 | --pcrpkey=tpm2-pcr-public.pem \ | |
312 | --bank=sha1 \ | |
313 | --bank=sha256 \ | |
314 | --private-key=tpm2-pcr-initrd-private.pem \ | |
315 | --public-key=tpm2-pcr-initrd-public.pem \ | |
316 | --phase=enter-initrd \ | |
317 | --append=tpm2-pcr-signature.json.tmp >tpm2-pcr-signature.json | |
318 | # objcopy \ | |
319 | --add-section .linux=vmlinux --change-section-vma .linux=0x2000000 \ | |
320 | --add-section .osrel=os-release.txt --change-section-vma .osrel=0x20000 \ | |
321 | --add-section .cmdline=cmdline.txt --change-section-vma .cmdline=0x30000 \ | |
322 | --add-section .initrd=initrd.cpio --change-section-vma .initrd=0x3000000 \ | |
323 | --add-section .splash=splash.bmp --change-section-vma .splash=0x100000 \ | |
324 | --add-section .dtb=devicetree.dtb --change-section-vma .dtb=0x40000 \ | |
325 | --add-section .pcrsig=tpm2-pcr-signature.json --change-section-vma .pcrsig=0x80000 \ | |
326 | --add-section .pcrpkey=tpm2-pcr-public.pem --change-section-vma .pcrpkey=0x90000 \ | |
327 | /usr/lib/systemd/boot/efi/linuxx64.efi.stub \ | |
328 | foo.efi</programlisting> | |
329 | </example> | |
330 | ||
331 | <para>Note that in this example the <literal>.pcrpkey</literal> PE section contains the key covering all | |
332 | boot phases. The <literal>.pcrpkey</literal> is used in the default policies of | |
333 | <command>systemd-cryptenroll</command> and <command>systemd-creds</command>. To use the stricter | |
334 | <filename>tpm-pcr-initrd-public.pem</filename>-bound policy, specify <option>--tpm2-public-key=</option> | |
335 | on the command line of those tools.</para> | |
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336 | </refsect1> |
337 | ||
338 | <refsect1> | |
339 | <title>Exit status</title> | |
340 | ||
341 | <para>On success, 0 is returned, a non-zero failure code otherwise.</para> | |
342 | </refsect1> | |
343 | ||
344 | <refsect1> | |
345 | <title>See Also</title> | |
346 | <para> | |
347 | <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
348 | <citerefentry><refentrytitle>systemd-stub</refentrytitle><manvolnum>7</manvolnum></citerefentry>, | |
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349 | <citerefentry project='man-pages'><refentrytitle>objcopy</refentrytitle><manvolnum>1</manvolnum></citerefentry>, |
350 | <citerefentry><refentrytitle>systemd-creds</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
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351 | <citerefentry><refentrytitle>systemd-cryptsetup@.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>, |
352 | <citerefentry><refentrytitle>systemd-pcrphase.service</refentrytitle><manvolnum>1</manvolnum></citerefentry> | |
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353 | </para> |
354 | </refsect1> | |
355 | ||
356 | </refentry> |