systemd systemd-measure 1 systemd-measure Pre-calculate and sign expected TPM2 PCR values for booted unified kernel images /usr/lib/systemd/systemd-measure OPTIONS Note: this command is experimental for now. While it is likely to become a regular component of systemd, it might still change in behaviour and interface. systemd-measure is a tool that may be used to pre-calculate and sign the expected TPM2 PCR 11 values that should be seen when a unified Linux kernel image based on systemd-stub7 is booted up. It accepts paths to the ELF kernel image file, initial ram disk image file, devicetree file, kernel command line file, os-release5 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 systemd-stub 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. The following commands are understood: status This is the default command if none is specified. This queries the local system's TPM2 PCR 11+12+13 values and displays them. The data is written in a similar format as the calculate command below, and may be used to quickly compare expectation with reality. calculate Pre-calculate the expected values seen in PCR register 11 after boot-up of a unified kernel image consisting of the components specified with --linux=, --osrel=, --cmdline=, --initrd=, --splash=, --dtb=, see below. Only --linux= is mandatory. (Alternatively, specify --current to use the current values of PCR register 11 instead.) sign As with the calculate command, pre-calculate the expected value seen in TPM2 PCR register 11 after boot-up of a unified kernel image. Then, cryptographically sign the resulting values with the private/public key pair (RSA) configured via --private-key= and --public-key=. This will write a JSON object to standard output that contains signatures for all specified PCR banks (see --pcr-bank=) below, which may be used to unlock encrypted credentials (see systemd-creds1) or LUKS volumes (see systemd-cryptsetup@.service8). This allows binding secrets to a set of kernels for which such PCR 11 signatures can be provided. Note that a TPM2 device must be available for this signing to take place, even though the result is not tied to any TPM2 device or its state. The following options are understood: --linux=PATH --osrel=PATH --cmdline=PATH --initrd=PATH --splash=PATH --dtb=PATH When used with the calculate or sign verb, configures the files to read the unified kernel image components from. Each option corresponds with the equally named section in the unified kernel PE file. The --linux= switch expects the path to the ELF kernel file that the unified PE kernel will wrap. All switches except --linux= are optional. Each option may be used at most once. --current When used with the calculate or sign verb, takes the PCR 11 values currently in effect for the system (which should typically reflect the hashes of the currently booted kernel). This can be used in place of --linux= and the other switches listed above. --bank=DIGEST Controls the PCR banks to pre-calculate the PCR values for – in case calculate or sign is invoked –, or the banks to show in the status output. May be used more then once to specify multiple banks. If not specified, defaults to the four banks sha1, sha256, sha384, sha512. --private-key=PATH --public-key=PATH These switches take paths to a pair of PEM encoded RSA key files, for use with the sign command. --tpm2-device=PATH Controls which TPM2 device to use. Expects a device node path referring to the TPM2 chip (e.g. /dev/tpmrm0). Alternatively the special value auto may be specified, in order to automatically determine the device node of a suitable TPM2 device (of which there must be exactly one). The special value list may be used to enumerate all suitable TPM2 devices currently discovered. # 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 calculate \ --linux=vmlinux \ --osrel=os-release.txt \ --cmdline=cmdline.txt \ --initrd=initrd.cpio \ --splash=splash.bmp \ --dtb=devicetree.dtb 11:sha1=d775a7b4482450ac77e03ee19bda90bd792d6ec7 11:sha256=bc6170f9ce28eb051ab465cd62be8cf63985276766cf9faf527ffefb66f45651 11:sha384=1cf67dff4757e61e5a73d2a21a6694d668629bbc3761747d493f7f49ad720be02fd07263e1f93061243aec599d1ee4b4 11:sha512=8e79acd3ddbbc8282e98091849c3530f996303c8ac8e87a3b2378b71c8b3a6e86d5c4f41ecea9e1517090c3e8ec0c714821032038f525f744960bcd082d937da # 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 \ --cmdline=cmdline.txt \ --initrd=initrd.cpio \ --splash=splash.bmp \ --dtb=devicetree.dtb \ --bank=sha1 \ --bank=sha256 \ --private-key=tpm2-pcr-private.pem \ --public-key=tpm2-pcr-public.pem > tpm2-pcr-signature.json Later on, enroll the signed PCR policy on a LUKS volume: # systemd-cryptenroll --tpm2-device=auto --tpm2-public-key=tpm2-pcr-public.pem --tpm2-signature=tpm2-pcr-signature.json /dev/sda5 And then unlock the device with the signature: # /usr/lib/systemd/systemd-cryptsetup attach myvolume /dev/sda5 - tpm2-device=auto,tpm2-signature=/path/to/tpm2-pcr-signature.json On success, 0 is returned, a non-zero failure code otherwise. systemd1, systemd-stub7, objcopy1, systemd-creds1, systemd-cryptsetup@.service8