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| -rw-r--r-- | docs/tpm-unlock.md | 68 |
1 files changed, 68 insertions, 0 deletions
diff --git a/docs/tpm-unlock.md b/docs/tpm-unlock.md index d60b5e7..4d17f1e 100644 --- a/docs/tpm-unlock.md +++ b/docs/tpm-unlock.md @@ -176,3 +176,71 @@ For an intended Secure Boot change, review the PCR 7 prediction before updating its policy. See [systemd-pcrlock](https://man.archlinux.org/man/systemd-pcrlock.8.en), [systemd-cryptenroll](https://man.archlinux.org/man/systemd-cryptenroll.1.en), and [cryptsetup-token](https://man.archlinux.org/man/cryptsetup-token.8.en). + +## Add the GPT partition policy + +The current root token already requires the pcrlock policy and signed PCR 11. +This change adds PCR 5 to the existing pcrlock policy. PCR 5 covers the disk +partition table. It does not bind file contents, the whole disk, or a kernel +version. Do not enroll a new LUKS token or remove the disk passphrase. + +Run this once on Halley2, outside aibox. Keep the disk passphrase and pcrlock +recovery PIN available. Stop if a check fails. Confirm that `/dev/nvme0n1` is +the disk that contains the root volume. Do not reboot during these steps. + +```sh +sudo cryptsetup open --test-passphrase --key-slot 0 /dev/nvme0n1p2 +sudo /usr/lib/systemd/systemd-pcrlock --strict=yes --pcr=7 --location=770 predict +sudo test ! -e /var/lib/pcrlock.d/600-gpt.pcrlock.d/generated.pcrlock +sudo test ! -e /var/lib/dotfiles/tpm-gpt/pcr7-policy.json +sudo install -d -m 0700 /var/lib/dotfiles/tpm-gpt +sudo cp /var/lib/systemd/pcrlock.json /var/lib/dotfiles/tpm-gpt/pcr7-policy.json +sudo cp /etc/systemd/system/systemd-pcrlock-make-policy.service.d/pcr7.conf \ + /var/lib/dotfiles/tpm-gpt/pcr7.conf +sudo /usr/lib/systemd/systemd-pcrlock lock-gpt /dev/nvme0n1 +sudo /usr/lib/systemd/systemd-pcrlock --strict=yes --pcr=5 --pcr=7 \ + --location=770 predict +just apply +sudo /usr/lib/systemd/systemd-pcrlock make-policy \ + --strict=yes --pcr=5 --pcr=7 --location=770 +sudo jq -e --slurpfile old /var/lib/dotfiles/tpm-gpt/pcr7-policy.json \ + '.nvIndex == $old[0].nvIndex and .nvHandle == $old[0].nvHandle' \ + /var/lib/systemd/pcrlock.json >/dev/null +just tpm-nvpcr-check +just tpm-unlock-check +``` + +The GPT command writes +`/var/lib/pcrlock.d/600-gpt.pcrlock.d/generated.pcrlock`. Stop and inspect +that file if it already exists. `just apply` installs the service override. +The `jq` check confirms that the existing TPM NV index is still in use. +The new checker requires both PCRs in the stored policy, a matching EFI boot +credential, and a strict prediction. Keep the backup on encrypted root storage. +The first normal reboot is the test of automatic unlock; do it only when you +are ready to enter the disk passphrase if TPM unlock fails. After that boot, +run both checks again and check `systemctl --failed`. + +If a planned partition change makes PCR 5 differ, use the disk passphrase to +boot. Review the new layout before you approve it. Then run `lock-gpt` again, +run the strict PCR 5+7 prediction, and update the policy with `make-policy`. +The pcrlock recovery PIN can authorize the update when the old policy no +longer matches. Do not approve an unexpected partition change. + +If the new policy blocks automatic unlock, use the disk passphrase. To return +to the saved PCR 7 policy, restore the old service override and update the +TPM policy. `--force` also rewrites the EFI credential when the prediction +equals an earlier policy. Do not copy the old JSON directly over the active +policy: the TPM NV index must be updated too. + +```sh +sudo install -m 0644 /var/lib/dotfiles/tpm-gpt/pcr7.conf \ + /etc/systemd/system/systemd-pcrlock-make-policy.service.d/pcr7.conf +sudo systemctl daemon-reload +sudo /usr/lib/systemd/systemd-pcrlock make-policy --force \ + --recovery-pin=query --strict=yes --pcr=7 --location=770 +sudo /usr/lib/systemd/systemd-pcrlock --strict=yes --pcr=7 --location=770 predict +``` + +The repo checker will then fail until you restore the PCR 5 setup. Do not +delete the saved policy or recovery PIN. The EFI boot test and root token +checks remain necessary because an offline prediction cannot prove unlock. |