biod/init/bio_crypto_init.conf

# Copyright 2018 The Chromium OS Authors. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.

description   "Binary to program bio sensors with TPM seed."
author        "chromium-os-dev@chromium.org"

# This job blocks the boot process in boot-services until all parts of this
# job/task are complete. This is important for the following two reasons:
# 1. For security purposes, we want to ensure that the secret seed is
#    transferred and cleared before other major processes are running.
# 2. We want to ensure that this process does not conflict with the firmware
#    in boot-update-firmware, which cannot have a direct dependence on this
#    upstart job.
start on starting boot-services
task

env LOG_DIR=/var/log/bio_crypto_init
env FP_DEV=/dev/cros_fp

pre-start script
  mkdir -m 755 -p "${LOG_DIR}"
  chown biod:biod "${LOG_DIR}"
  if [ -c "${FP_DEV}" ]; then
    # Since we are running before udev executes, we need to manually make the
    # dev node accessible inside the sandbox.
    chown root:biod "${FP_DEV}"
    chmod 660 "${FP_DEV}"
  else
    # No point in continuing if there isn't a device node
    stop
    exit 0
  fi
end script

# Here (in order) are a list of the args added:
# - Create and enter new UTS namespace (hostname/NIS domain name).
# - Create and enter new network namespace.
# - Create and enter new IPC namespace.
# - Create and enter new cgroup namespace.
# - Create and enter new PID namespace.
# - Same options as minimalistic-mountns except we do not mount /dev/log because
#   it doesn't necessarily exist since the logging daemon hasn't started yet.
# - Get a writeable and empty /run tmpfs path.
# - Mount the /run/biod_seed file.
# - Get a writeable and empty /var tmpfs path.
# - Mount the log directory in it.
# - Mount the FPMCU dev node.
# - Run as biod user and group.
# - Inherit supplementary groups from from user biod.
# - Grant no caps.
# - No new privileges (no_new_privs).
# - Use bio_crypto_init seccomp policy.
# - Execute the binary.
exec minijail0                                                         \
  --uts                                                                \
  -e                                                                   \
  -l                                                                   \
  -N                                                                   \
  -p                                                                   \
  -v -P /mnt/empty -b / -b /proc -t -r --mount-dev                     \
  -k 'tmpfs,/run,tmpfs,MS_NODEV|MS_NOEXEC|MS_NOSUID,mode=755,size=10M' \
  -b /run/bio_crypto_init,,1                                           \
  -k 'tmpfs,/var,tmpfs,MS_NODEV|MS_NOEXEC|MS_NOSUID,mode=755,size=10M' \
  -b ${LOG_DIR},,1                                                     \
  -b ${FP_DEV}                                                         \
  -u biod -g biod                                                      \
  -G                                                                   \
  -c 0                                                                 \
  -n                                                                   \
  -S /usr/share/policy/bio-crypto-init-seccomp.policy                  \
  -- /usr/bin/bio_crypto_init                                          \
  --log_dir=${LOG_DIR}

# Ensure the /run file is cleaned up in case it still exists.
post-stop script
  rm -f /run/bio_crypto_init/seed
end script