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Initial Secure boot setup

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Audiobuzz
2026-06-20 00:40:59 +00:00
parent b67a23e718
commit ec92417312
4 changed files with 281 additions and 7 deletions
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.gitea/workflows/gitea-main-ci.yaml
+40 -7
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@@ -8,16 +8,19 @@
# shell-local post-processors extract artifacts, build the UKI (ukify), and
# build+push the OCI release image.
#
# This is an UNSIGNED (lab) build: sb_key/sb_cert are intentionally NOT passed,
# so build-oci.sh emits its loud unsigned-UKI warning. A production fleet must
# sign in CI/HSM -- see the "TODO: wire SB_KEY/SB_CERT" step below.
# Signed when the SB_KEY/SB_CERT secrets are set; otherwise an UNSIGNED (lab)
# build where build-oci.sh emits its loud unsigned-UKI warning. Signing runs
# shell-local on the runner (not in the build VM); the key is staged to
# RUNNER_TEMP and shredded after. See docs/secure-boot-keys.md.
#
# Required Gitea repo secrets:
# REGISTRY_USERNAME - registry user for `oci_image` (oci_push=true)
# REGISTRY_TOKEN - registry password/token
# SSH_AUTHORIZED_KEY - public key for the sudo admin user; empty => no admin
# user + root left unlocked (lab). Set it to lock root.
# # SB_KEY, SB_CERT - (future) Secure Boot signing key + cert for signed UKIs
# SB_KEY, SB_CERT - Secure Boot signing: the `db` PRIVATE key (PEM) + its
# cert (PEM). Empty => unsigned lab build. PK/KEK are NOT
# here (offline/HSM). Generate per docs/secure-boot-keys.md.
#
# Runner: needs KVM (qemu accelerator=kvm) and the build-host tooling installed
# below (libguestfs, erofs-utils, cryptsetup, jq, ukify, buildah).
@@ -176,11 +179,32 @@ jobs:
--password "${{ secrets.PACKAGE_TOKEN }}" \
git.bitasylum.org
-
name: Materialize Secure Boot signing material
# sb_key/sb_cert are consumed by ukify as FILE PATHS (not values), and the
# signing post-processor runs shell-local on THIS runner (not in the build
# VM), so write the secrets to runner-temp files and pass their paths. The
# `db` PRIVATE key is the only signing key here; PK/KEK stay offline (see
# docs/secure-boot-keys.md). If SB_KEY is unset, this no-ops and the build
# falls back to an UNSIGNED lab UKI (the loud warning stays).
if: ${{ secrets.SB_KEY != '' }}
env:
SB_KEY: ${{ secrets.SB_KEY }} # db private key (PEM) — secret
SB_CERT: ${{ secrets.SB_CERT }} # db cert (PEM) — public, kept as a secret for convenience
run: |
umask 077
d="$RUNNER_TEMP/sb"; mkdir -p "$d"
printf '%s\n' "$SB_KEY" > "$d/db.key"
printf '%s\n' "$SB_CERT" > "$d/db.crt"
echo "SB_KEY_FILE=$d/db.key" >> "$GITHUB_ENV"
echo "SB_CERT_FILE=$d/db.crt" >> "$GITHUB_ENV"
echo "Secure Boot signing material staged (signed UKI build)."
-
name: packer build (UKI + OCI release image)
# UNSIGNED lab build: sb_key/sb_cert deliberately omitted.
# TODO: wire SB_KEY/SB_CERT secrets for a signed UKI:
# -var sb_key=${{ secrets.SB_KEY }} -var sb_cert=${{ secrets.SB_CERT }}
# Signed when SB_KEY/SB_CERT secrets are set (paths exported above);
# UNSIGNED lab build (loud warning) when they're empty. sb_key/sb_cert are
# PATHS, never values — see the materialize step and docs/secure-boot-keys.md.
run: |
packer build -color=false -on-error=abort \
-var image_version="${{ steps.vars.outputs.image_version }}" \
@@ -190,11 +214,20 @@ jobs:
-var disable_dot1x=${{ env.DISABLE_DOT1X }} \
-var nvmet_traddr="${{ env.NVMET_TRADDR }}" \
-var ssh_authorized_key="${{ secrets.SSH_AUTHORIZED_KEY }}" \
-var sb_key="${SB_KEY_FILE:-}" \
-var sb_cert="${SB_CERT_FILE:-}" \
-var kiosk_url="${{ env.KIOSK_URL }}" \
-var boot_splash=${{ env.BOOT_SPLASH }} \
-var enable_stig=${{ env.ENABLE_STIG }} \
.
-
name: Shred Secure Boot signing key
# Remove the private key from the runner FS even if the build failed.
# (RUNNER_TEMP is also wiped per-job on ephemeral runners — belt + braces.)
if: always()
run: shred -u "$RUNNER_TEMP/sb/db.key" 2>/dev/null || rm -f "$RUNNER_TEMP/sb/db.key" 2>/dev/null || true
-
name: STIG deviations report (report-only)
# The build downloaded the post-remediation scan (stig-arf.xml +
diskless.pkr.hcl
+14
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@@ -253,6 +253,20 @@ build {
# dracut warns and silently falls back to gzip (a larger initramfs).
"dnf -y install wpa_supplicant tpm2-tools tpm2-tss nvme-cli cryptsetup dracut-network NetworkManager zstd openssl",
# EFI / Secure Boot management tools, for MANUAL key enrollment over SSH on
# a workstation in Setup Mode: efitools (efi-updatevar, efi-readvar,
# cert-to-efi-sig-list, sign-efi-sig-list, KeyTool) + efivar/mokutil/
# efibootmgr companions. See docs/secure-boot-keys.md ("Manual enrollment");
# auto-enroll is TODO #10. They write to efivarfs
# (/sys/firmware/efi/efivars), NOT the read-only root, so they work at
# runtime; RPM-installed => already fapolicyd-trusted (no STIG trust edit).
# efitools is EPEL-only on el9: enable EPEL just to pull it, then drop the
# repo so a non-kiosk image's repo set is unchanged (kiosk builds re-add it).
"dnf -y install efivar mokutil efibootmgr",
"rpm -q efitools >/dev/null 2>&1 || { dnf -y install epel-release && dnf -y install efitools && EFITOOLS_EPEL=1; } || true",
"rpm -q efitools >/dev/null 2>&1 && echo '==> EFI Secure Boot tools installed (efitools + efivar/mokutil/efibootmgr)' || echo 'WARNING: efitools not installed (EPEL unavailable?) — manual SB enrollment tooling missing' >&2",
"[ \"$${EFITOOLS_EPEL:-0}\" = 1 ] && dnf -y remove epel-release >/dev/null 2>&1 || true",
# Plymouth boot splash. The custom scripted 'fleet' theme renders the
# security-handshake checklist driven by the dracut hooks
# (`plymouth update --status=...`). plymouth-plugin-label gives Image.Text
docs/TODO.md
+57
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@@ -624,6 +624,8 @@ smoke test.
by the serving dnsmasq — drop the hardcoded `192.168.50.10`.
- **Signing:** wire `sb_key`/`sb_cert` (CI/HSM secrets) for a signed UKI; enable
Secure Boot on targets. Until then the loud unsigned warning must stay.
**Key generation + enrolment procedure: [secure-boot-keys.md](secure-boot-keys.md)**
(the PK/KEK/db trio; `db` = `sb_key`/`sb_cert`, PK/KEK stay offline).
- **Bench-verify on the secure path** (swtpm + hostapd + FreeRADIUS,
`disable_dot1x=false`) — the items deferred this session:
- NM port secure path: `en*` UNMANAGED + `macsec0` MANAGED/renewing, MKA
@@ -687,3 +689,58 @@ Tips the balance toward "do it" only if: we start managing the **serving hosts**
roles to amortise — currently they're docker-compose), provisioning grows much
more branchy, or we want molecule-tested hardening roles validated without a
full ~17-min Packer build.
## [ ] 10. (OPTIONAL) Secure Boot cert auto-enrollment for provisioning
Speed up bringing up new workstations: bake the **public** PK/KEK/db certs into an
image, detect Secure Boot **Setup Mode** at boot, and auto-enroll them with
efitools (`efi-updatevar`/`KeyTool`) so a fresh/reset box adopts the fleet trust
root without a manual firmware-setup visit. Pairs with #8 (signing) +
[secure-boot-keys.md](secure-boot-keys.md).
**What's safe:** the certs are public (no key material — only the **db** private
key signs, and it stays in CI/HSM, invariant #7); Setup Mode accepts
*unauthenticated* writes to PK/KEK/db, so public certs (ESL) are sufficient. It's
fleet-generic (no per-host state, invariant #1) and deterministic (reproducible
verity hash).
**The real risk — provisioning-time TOFU (trust-on-first-use):** in Setup Mode
Secure Boot isn't enforcing, so the enroller runs as *unverified* code, and the
fleet's UEFI **HTTP boot is unauthenticated** in that state. An on-path attacker
during provisioning can serve a malicious image that enrolls **their** PK/KEK/db —
the box then "has Secure Boot" but trusts the attacker. Auto-enroll is only as
trustworthy as the provisioning channel, and it removes the physical-presence
approval gate. So treat it as a controlled-environment provisioning step, not an
always-on behaviour.
**Optional separate provisioning UKI (preferred shape):** build a dedicated
**provisioning UKI** that carries the certs + the enroll logic, instead of arming
the enroller in the production image. Keeps the standing footgun out of the normal
image (a factory reset + tampered image can't silently re-root trust), and lets
the enroller be a one-shot, attended/isolated step. The production UKI never
enrolls.
- Build it as a separate Packer target / flag (e.g. `provisioning=true`) →
its own small UKI; signed or unsigned (it runs in Setup Mode anyway, but sign
it so it *also* boots once keys are enrolled / for re-runs).
- Or a tiny standalone EFI tool (KeyTool-style) served alongside, not a full OS.
**Mitigations (do these regardless of UKI vs separate UKI):**
- Run provisioning on a **trusted, isolated VLAN** (or a physically controlled
bench) — the integrity Setup Mode can't give must come from the environment.
- **Gate** enrollment behind an explicit provisioning mode / one-shot token;
never arm it on every boot of the production image.
- **Read-back verify before declaring success:** `efi-readvar` the enrolled
PK/KEK/db and compare fingerprints to the values baked in; mismatch = fail
loudly (turns silent TOFU into tamper-evidence).
- **Audit** the enrollment event + read-back fingerprints to the collector.
- **Keep the Microsoft UEFI CA in `db`** (or enroll your db alongside it) unless
every NIC/GPU option ROM is covered by your keys — clearing MS db can break
signed **option ROMs** (NIC PXE/HTTP-boot, GPU init), bricking the boot path.
- **PCR 7 check:** enrollment changes the Secure Boot measurement in PCR 7;
confirm nothing the fleet seals to the TPM (the EAP-TLS key at `0x81010001`,
NV cert) is PCR-7-policy-bound before relying on this.
**Decision before building:** auto-enroll trades assurance for convenience and is
reasonable for a controlled fleet; the highest-assurance path is attended/firmware
or manufacturer pre-provisioning. Default recommendation: **separate provisioning
UKI + isolated VLAN + read-back verify.**
docs/secure-boot-keys.md
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@@ -0,0 +1,170 @@
# Secure Boot key generation & enrollment — diskless fleet
The fleet boots a **signed UKI directly via systemd-stub** (no shim, no GRUB), so
UEFI Secure Boot verifies the UKI against keys **you** enrol in firmware. This
doc generates the three Secure Boot keys (the "trio": **PK, KEK, db**), enrols
them, and wires the `db` key into the build.
> **Invariant #7:** signing keys never enter the build VM or this repo. The
> commands below produce key material that lives **offline / in an HSM**. Only the
> **db** key signs UKIs routinely, and the build receives it as a *path*
> (`sb_key`/`sb_cert`) on the CI/HSM host — never committed, never echoed in logs.
> Treat every `*.key` file here as secret; never check one into git.
## The trio — roles and where each lives
| Key | Role | Used by | Where it lives |
|---|---|---|---|
| **PK** (Platform Key) | Root of trust; controls who may update the KEK. Setting it locks Secure Boot into User Mode. | Firmware enrolment only | **Offline / HSM**, used once (and for KEK rotation) |
| **KEK** (Key Exchange Key) | Signs updates to `db`/`dbx`. | Firmware enrolment only | **Offline / HSM** |
| **db** (Signature Database) | Signs the bootable UKI. | **The fleet build** — `sb_key`/`sb_cert` ([../scripts/build-oci.sh](../scripts/build-oci.sh) → ukify/sbsign) | HSM/CI signing host |
Trust chain at enrolment: **PK signs KEK → KEK signs db → db signs the UKI.**
Only `db` is online (it signs every release; the UKI cmdline is immutable once
signed — invariant #6 — so re-signing is part of each build). PK and KEK are only
needed to rotate keys later, so they stay offline.
## Tooling
```bash
# Fedora / RHEL: dnf install openssl efitools sbsigntools
# Debian / Ubuntu: apt install openssl efitools sbsigntool
```
## 1. Generate the three key/cert pairs
```bash
GUID=$(uuidgen); echo "$GUID" > GUID.txt # owner GUID for the EFI variables
# Platform Key
openssl req -newkey rsa:2048 -nodes -keyout PK.key -new -x509 -sha256 -days 3650 \
-subj "/CN=Fleet Platform Key/" -out PK.crt
# Key Exchange Key
openssl req -newkey rsa:2048 -nodes -keyout KEK.key -new -x509 -sha256 -days 3650 \
-subj "/CN=Fleet KEK/" -out KEK.crt
# Signature DB key <-- this pair becomes sb_key / sb_cert
openssl req -newkey rsa:2048 -nodes -keyout db.key -new -x509 -sha256 -days 3650 \
-subj "/CN=Fleet db/" -out db.crt
```
`rsa:2048` is the maximally firmware-compatible size for the enrolled variables;
`4096` works on most modern UEFI but some implementations reject it for
PK/KEK/db. The PEM `db.key`/`db.crt` are exactly what sbsign/ukify consume.
## 2. Convert to signed EFI variable updates (`.auth`)
```bash
for v in PK KEK db; do cert-to-efi-sig-list -g "$GUID" $v.crt $v.esl; done
sign-efi-sig-list -g "$GUID" -k PK.key -c PK.crt PK PK.esl PK.auth # PK self-signs
sign-efi-sig-list -g "$GUID" -k PK.key -c PK.crt KEK KEK.esl KEK.auth # PK signs KEK
sign-efi-sig-list -g "$GUID" -k KEK.key -c KEK.crt db db.esl db.auth # KEK signs db
```
## 3. Enrol into firmware
Put the firmware in **Setup Mode** first (clear the existing keys in the UEFI
setup screen). Then enrol **db and KEK before PK** — setting PK last is what flips
the firmware out of Setup Mode and turns Secure Boot on:
```bash
efi-updatevar -f db.auth db
efi-updatevar -f KEK.auth KEK
efi-updatevar -f PK.auth PK # do this LAST
```
Alternatively, enrol the `.auth`/`.esl` files via the firmware's own
"enrol key from file" UI or `KeyTool.efi` — useful for headless fleet hardware
where this is scripted into provisioning.
> The fleet uses a UKI with **no shim and no Microsoft keys**, so no MOK is
> needed. If a host must also boot vendor-signed media, *add* your `db` alongside
> Microsoft's UEFI CA instead of clearing it.
### Manual enrollment on a fleet workstation (over SSH)
The build bakes the EFI management tools into the image (`efitools` +
`efivar`/`mokutil`/`efibootmgr`, installed in the main package provisioner), so
you can enrol keys **manually over SSH** on a booted workstation that is in Setup
Mode — handy for provisioning before the automated flow (TODO #10) exists. The
tools write to `efivarfs` (`/sys/firmware/efi/efivars`), not the read-only root,
so they work at runtime; they're RPM-installed so fapolicyd already trusts them.
```bash
# on the workstation (as the sudo admin):
mokutil --sb-state # check Secure Boot / Setup Mode
efi-readvar # dump current PK/KEK/db/dbx
# copy your PK.auth/KEK.auth/db.auth (or .esl) onto the host, then in Setup Mode:
sudo efi-updatevar -f db.auth db
sudo efi-updatevar -f KEK.auth KEK
sudo efi-updatevar -f PK.auth PK # last — leaves Setup Mode
efi-readvar # read back + confirm fingerprints match
```
Only the **public** certs/`.esl`/`.auth` need to reach the workstation — never
copy `PK.key`/`KEK.key`/`db.key` onto a host.
## 4. Wire `db` into the build
```bash
packer build -var image_version=X.Y.Z \
-var sb_key=/path/to/db.key \
-var sb_cert=/path/to/db.crt \
-var oci_image=<registry>/fleet-boot .
```
ukify signs `fleet-<ver>.efi` with `db`; the enrolled `db` cert lets firmware
verify it. Without these vars the build stays **unsigned** (lab-only, with the
loud warning). In CI, `sb_key`/`sb_cert` are secret paths on the HSM/signing host.
## Signing in CI (Gitea Actions)
`sb_key`/`sb_cert` **can** be Gitea repo secrets, with one wrinkle: ukify consumes
them as **file paths**, not values, and the signing post-processor runs
**shell-local on the runner** (not in the build VM — consistent with invariant
#7). So the job materializes the secrets to runner-temp files, passes the paths,
and shreds the key afterward. This is wired in
[../.gitea/workflows/gitea-main-ci.yaml](../.gitea/workflows/gitea-main-ci.yaml)
(steps: *Materialize Secure Boot signing material* → *packer build* → *Shred
Secure Boot signing key*). Set repo secrets **`SB_KEY`** (the `db` private key,
PEM) and **`SB_CERT`** (the `db` cert, PEM); leave them unset for an unsigned lab
build.
Caveats:
- **Only `db` belongs in CI.** PK and KEK never leave the offline/HSM store.
- `SB_CERT` is a public cert (not secret); kept as a secret only for convenience.
- A CI secret puts the private key **in plaintext on the runner FS** for the
duration of the build — only as safe as the runner. Use a **trusted,
ephemeral/self-hosted** runner, ensure secrets are **not exposed to fork/PR
builds**, and rely on `RUNNER_TEMP` wipe + the shred step. Gitea masks secret
values in logs, and `build-oci.sh` passes the *path* (not content) to ukify, so
the key won't leak into logs.
- **Stronger (production target):** keep `db.key` in an **HSM/PKCS#11** token or
KMS and sign *through* it, so the raw key never touches the runner disk. The
CI-secret flow is a reasonable interim; the HSM flow is the invariant-#7 ideal
(TODO #8).
## Key hygiene & lifecycle
- **PK.key and KEK.key go offline / into an HSM and stay there.** They are only
needed to rotate keys; routine signing uses **db.key** only.
- **Production ideal:** keep `db.key` in an HSM/PKCS#11 token and have
sbsign/ukify sign *through* it rather than reading a file from disk.
- **Validity:** `-days 3650` is 10 years; pick a rotation policy. Rotating `db`
= sign new `db.esl` with KEK, push the `db` variable update, re-sign UKIs.
- **dbx** (the revocation list) is a fourth, optional variable — manage it to
blacklist a compromised `db` cert.
- **Lab shortcut:** [`sbctl`](https://github.com/Foxboron/sbctl)
(`sbctl create-keys` → `sbctl enroll-keys`) generates and enrols the whole trio
and tracks signed files — convenient for a dev box, but it keeps keys as local
files, so for the fleet's HSM/offline-PK model use the manual flow above for
PK/KEK.
## Related
- Invariants #6 (UKI cmdline immutable once signed), #7 (keys never in repo/VM),
#5 (roothash↔UKI hard gate) — [../CLAUDE.md](../CLAUDE.md).
- Signing is the production-posture step in [TODO.md](TODO.md) #8.
- FIPS is currently off and is to be revisited alongside signing/Secure Boot
([stig-deviations.md](stig-deviations.md) #5).