path: root/luks-tpm

#!/bin/bash

# Copyright 2017 Corey Hinshaw <coreyhinshaw@gmail.com>
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.

usage () {
  cat <<EOF
Usage: luks-tpm [OPTION]... DEVICE ACTION
Manage the LUKS TPM keys on DEVICE

Actions:
  temp       Set a temporary LUKS passphrase
  reset      Reset the LUKS TPM key using a passphrase
  replace    Replace (overwrite) a LUKS TPM key

Options:
  -h         Print this help text
  -m PATH    Mount point for the tmpfs file system used to store TPM keyfiles
             Default: /root/keyfs
  -k PATH    Sealed TPM keyfile path
             Default: /boot/keyfile.enc
  -t NUMBER  LUKS slot number for the TPM keyfile
             Default: 1
  -r NUMBER  LUKS slot number for temporary reset passphrase
             Default: 2
  -p NUMBER  PCRs used to seal LUKS keyfile. May be specified more than once
             Default: 0-7
  -z         Use the TPM SRK well-known password
EOF
}

add_temp_key() {
  tpm_unsealdata -i "$SEALED_KEYFILE" -o "$KEYFILE" $WELL_KNOWN

  echo "Preparing to set a temporary LUKS passphrase..."
  if cryptsetup luksAddKey --key-slot $RESET_KEY_SLOT --key-file "$KEYFILE" $ROOT_DEVICE < /dev/tty; then
    echo "After booting into the current kernel, run"
    echo "  luks-tpm $(echo $ORIGINAL_ARGS | sed 's/temp$/reset/')"
    echo "to generate a new TPM keyfile and remove this temporary key"
  else
    echo "A temporary passphrase was not set" >&2
    RETURN_CODE=5
  fi
}

reset_tpm_key() {
  read -s -p "Enter any existing LUKS passphrase: " PASSPHRASE
  echo

  echo "Generating new LUKS key..."
  generate_keyfile

  echo "Removing current TPM key from slot $TPM_KEY_SLOT..."
  echo $PASSPHRASE | cryptsetup luksKillSlot $ROOT_DEVICE $TPM_KEY_SLOT

  echo "Adding new key to slot $TPM_KEY_SLOT..."
  echo $PASSPHRASE | cryptsetup luksAddKey $ROOT_DEVICE "$KEYFILE" --key-slot $TPM_KEY_SLOT
  addkey=$?

  echo "Sealing keyfile with the TPM..."
  tpm_sealdata $PCRS -i "$KEYFILE" -o "$SEALED_KEYFILE" $WELL_KNOWN
  seal=$?

  if [ $addkey -eq 0 ] && [ $seal -eq 0 ]; then
    echo "Removing temporary passphrase from slot $RESET_KEY_SLOT..."
    cryptsetup luksKillSlot --key-file "$KEYFILE" $ROOT_DEVICE $RESET_KEY_SLOT
  else
    echo "There was an error resetting the TPM key in slot $TPM_KEY_SLOT!" >&2
    echo "The temporary reset ket in slot $RESET_KEY_SLOT has not been removed." >&2
    RETURN_CODE=4
  fi
}

replace_tpm_key() {
  ORIGINAL_KEYFILE="$KEYFILE.orig"

  echo "Usealing current keyfile..."
  tpm_unsealdata -i "$SEALED_KEYFILE" -o "$ORIGINAL_KEYFILE" $WELL_KNOWN

  generate_keyfile

  echo "Replacing LUKS key..."
  if cryptsetup luksChangeKey $ROOT_DEVICE "$KEYFILE" --key-slot $TPM_KEY_SLOT --key-file "$ORIGINAL_KEYFILE"; then
    echo "Sealing new keyfile with the TPM..."
    if ! tpm_sealdata $PCRS -i "$KEYFILE" -o "$SEALED_KEYFILE" $WELL_KNOWN; then
      echo "There was an error sealing the new keyfile!" >&2
      RETURN_CODE=7
    fi
  else
    echo "There was an error replacing the TPM key in slot $TPM_KEY_SLOT!" >&2
    RETURN_CODE=6
  fi
}

create_tmpfs() {
  mkdir -p "$TMPFS_MOUNT"
  if ! mount tmpfs "$TMPFS_MOUNT" -t tmpfs -o size=1m; then
    echo "Could not create tmpfs. Aborting..." >&2
    exit 3
  fi
  chmod 700 "$TMPFS_MOUNT"
}

destroy_tmpfs() {
  umount "$TMPFS_MOUNT"
}

generate_keyfile() {
  dd bs=512 count=4 if=/dev/urandom of="$KEYFILE" > /dev/null 2>&1
}

ORIGINAL_ARGS="$@"
TMPFS_MOUNT=/root/keyfs
SEALED_KEYFILE=/boot/keyfile.enc
TPM_KEY_SLOT=1
RESET_KEY_SLOT=2
PCRS="-p 0 -p 1 -p 2 -p 3 -p 4 -p 5 -p 6 -p 7"
WELL_KNOWN=""

while getopts ":hm:k:t:r:p:z" opt; do
  case $opt in
    h)
      usage
      exit 0
      ;;
    m)
      TMPFS_MOUNT="$OPTARG"
      ;;
    k)
      SEALED_KEYFILE="$OPTARG"
      ;;
    t)
      if [[ ! $OPTARG =~ ^-?[0-9]+$ ]] || [ $OPTARG -lt 0 ] || [ $OPTARG -gt 7 ]; then
        echo "Invalid TPM key slot: $OPTARG" >&2
	exit 1
      fi
      TPM_KEY_SLOT=$OPTARG
      ;;
    r)
      if [[ ! $OPTARG =~ ^-?[0-9]+$ ]] || [ $OPTARG -lt 0 ] || [ $OPTARG -gt 7 ]; then
        echo "Invalid reset key slot: $OPTARG" >&2
	exit 1
      fi
      RESET_KEY_SLOT=$OPTARG
      ;;
    p)
      if [[ ! $OPTARG =~ ^-?[0-9]+$ ]] || [ $OPTARG -lt 0 ] || [ $OPTARG -gt 23 ]; then
        echo "Invalid PCR: $OPTARG" >&2
	exit 1
      fi

      if [ -z $pcr_option ]; then
        PCRS="-p $OPTARG"
      else
        PCRS="$PCRS -p $OPTARG"
      fi
      pcr_option=1
      ;;
    z)
      WELL_KNOWN="-z"
      ;;
    \?)
      echo "Invalid option: -$OPTARG" >&2
      usage >2&
      exit 1
      ;;
    :)
      echo "Option -$OPTARG requires an argument." >&2
      exit 1
      ;;
  esac
done

shift $((OPTIND-1))

ROOT_DEVICE="$1"
KEYFILE="$TMPFS_MOUNT/keyfile"
RETURN_CODE=0

if [ -z $ROOT_DEVICE ]; then
  echo "Device not specified!" >&2
  usage >&2
  exit 1
fi

if [ $EUID -ne 0 ]; then
  echo "Must be run as root" >&2
  exit 2
fi

case "$2" in
  temp) ACTION=add_temp_key;;
  reset) ACTION=reset_tpm_key;;
  replace) ACTION=replace_tpm_key;;
  *)
    echo "Invalid action!" >&2
    usage >&2
    exit 1
    ;;
esac

create_tmpfs
$ACTION
destroy_tmpfs
exit $RETURN_CODE