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"""Read-only checks for Halley2's signed NvPCR UKIs."""
import hashlib
import json
import os
import subprocess
import sys
from pathlib import Path
BOOT = Path("/boot/EFI/Linux")
PUBLIC_KEY = Path("/etc/systemd/tpm2-pcr-public-key.pem")
SB_CERT = Path("/var/lib/sbctl/keys/db/db.pem")
IMAGES = (
"arch-linux-hardened.efi",
"arch-linux-hardened-fallback.efi",
"arch-linux-lts.efi",
"arch-linux-lts-fallback.efi",
)
MEASUREMENT_OPTIONS = (
"tpm2-device=auto",
"tpm2-measure-pcr=15",
"tpm2-measure-keyslot-nvpcr=cryptsetup",
)
INITRD_UNITS = (
"systemd-tpm2-setup-early.service",
"systemd-pcrnvdone.service",
"systemd-pcrextend.socket",
"systemd-pcrextend@.service",
)
def run(*command: str) -> str:
result = subprocess.run(command, capture_output=True, text=True, check=True)
return result.stdout
def check_sections(sections: dict, public_key: bytes) -> None:
public = sections.get(".pcrpkey")
if (
not isinstance(public, dict)
or public.get("sha256") != hashlib.sha256(public_key).hexdigest()
):
raise ValueError("UKI does not embed the expected PCR public key")
signature = sections.get(".pcrsig")
if not isinstance(signature, dict) or not isinstance(signature.get("text"), str):
raise TypeError("UKI has no readable PCR signatures")
policies = json.loads(signature["text"])
if not isinstance(policies, dict) or not any(
isinstance(item, dict)
and item.get("pcrs") == [11]
and item.get("ref") == "initrd"
and isinstance(item.get("sig"), str)
and bool(item["sig"])
for item in policies.get("sha256", [])
):
raise ValueError("UKI has no signed initrd PCR 11 policy")
cmdline = sections.get(".cmdline")
if not isinstance(cmdline, dict) or not isinstance(cmdline.get("text"), str):
raise TypeError("UKI has no kernel command line")
args = cmdline["text"].split()
roots = [arg.split("=", 2)[1] for arg in args if arg.startswith("rd.luks.name=")]
if len(roots) != 1:
raise ValueError("UKI must specify exactly one LUKS root device")
options = [
arg.removeprefix("rd.luks.options=")
for arg in args
if arg.startswith("rd.luks.options=")
]
if len(options) != 1 or not options[0].startswith(roots[0] + "="):
raise ValueError("Root measurement options have the wrong LUKS UUID")
selected = options[0].split("=", 1)[1].split(",")
if not all(option in selected for option in MEASUREMENT_OPTIONS):
raise ValueError("Root measurement or TPM unlock option is missing")
def check_initrd_listing(listing: str) -> None:
members = {line.strip().lstrip("./") for line in listing.splitlines()}
for unit in INITRD_UNITS:
if f"usr/lib/systemd/system/{unit}" not in members:
raise ValueError(f"UKI initrd lacks {unit}")
def check_image(path: Path, public_key: bytes) -> None:
sections = json.loads(
run(
"ukify",
"--json=short",
"--section=.pcrpkey:binary",
"--section=.pcrsig:text",
"--section=.cmdline:text",
"inspect",
str(path),
)
)
if not isinstance(sections, dict) or "_profiles" in sections:
raise ValueError(f"Unsupported multi-profile UKI: {path}")
check_sections(sections, public_key)
check_initrd_listing(run("lsinitcpio", "--list", str(path)))
run("sbverify", "--cert", str(SB_CERT), str(path))
print(f"verified: {path}")
def check_boot() -> None:
active = Path("/proc/cmdline").read_text()
if not all(option in active for option in MEASUREMENT_OPTIONS):
raise ValueError("Current boot did not use the NvPCR root options")
nvpcrs = run("systemd-analyze", "nvpcrs", "--no-pager")
for name in ("cryptsetup", "hardware", "login", "verity"):
if name not in nvpcrs:
raise ValueError(f"NvPCR {name} is not available")
run(
"/usr/lib/systemd/systemd-pcrlock",
"--strict=yes",
"--pcr=7",
"--location=770",
"predict",
)
failed = run("systemctl", "--failed", "--no-legend", "--no-pager")
if failed.strip():
raise ValueError("Systemd has failed units; inspect systemctl --failed")
print(
"verified: current boot options, NvPCR availability, and strict PCR 7 prediction"
)
def main() -> int:
if os.geteuid() != 0 or Path("/etc/hostname").read_text().strip() != "halley2":
raise ValueError("Run as root on Halley2")
public_key = PUBLIC_KEY.read_bytes()
if not public_key:
raise ValueError("Missing PCR public key")
paths = [Path(arg) for arg in sys.argv[1:]] or [BOOT / name for name in IMAGES]
for path in paths:
check_image(path, public_key)
if len(sys.argv) == 1:
check_boot()
return 0
if __name__ == "__main__":
try:
sys.exit(main())
except (OSError, TypeError, ValueError, subprocess.CalledProcessError) as exc:
print(f"NvPCR check failed: {exc}", file=sys.stderr)
sys.exit(1)
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