dracut: added new module masterkey

This module initializes a trusted/user kernel master key that will be used
to decrypt other encrypted keys.

Signed-off-by: Roberto Sassu <roberto.sassu@polito.it>
Acked-by: Gianluca Ramunno <ramunno@polito.it>

dracut.kernel.7.xml

@@ -703,6 +703,23 @@ rd.znet=ctc,0.0.0600,0.0.0601,0.0.0602,protocol=bar</programlisting></para>
         </varlistentry>
       </variablelist>
     </refsect2>
+   <refsect2>
+      <title>Kernel keys</title>
+      <variablelist>
+        <varlistentry>
+          <term><envar>masterkey=</envar><replaceable>&lt;kernel master key path name&gt;</replaceable></term>
+          <listitem>
+            <para>Set the path name of the kernel master key. e.g.: <programlisting>masterkey=/etc/keys/kmk-trusted.blob</programlisting></para>
+          </listitem>
+        </varlistentry>
+        <varlistentry>
+          <term><envar>masterkeytype=</envar><replaceable>&lt;kernel master key type&gt;</replaceable></term>
+          <listitem>
+            <para>Set the type of the kernel master key. e.g.: <programlisting>masterkeytype=trusted</programlisting></para>
+          </listitem>
+        </varlistentry>
+      </variablelist>
+    </refsect2>
     <refsect2>
       <title>Deprecated, renamed Options</title>
       <para>Here is a list of options, which were used in dracut prior to version 008, and their new replacement.</para>

modules.d/97masterkey/README

@@ -0,0 +1,68 @@
+# Directions for creating the kernel master key that will be used for
+# encrypting/decrypting other keys.
+
+# A trusted key is a TPM random number, which is only ever exposed to
+# userspace as an encrypted datablob. A trusted key can be sealed to a
+# set of PCR values. For more details on trusted keys, refer to the
+# kernel keys-trusted-encrypted.txt documentation.
+$ keyctl add trusted kmk-trusted "new 32" @u
+801713097
+
+# For those systems which don't have a TPM, but want to experiment with
+# encrypted keys, create a user key of 32 random bytes. Unlike
+# trusted/encrypted keys, user type key data is visible to userspace.
+$ keyctl add user kmk-user "`dd if=/dev/urandom bs=1 count=32 2>/dev/null`" @u
+144468621
+
+# Save the kernel master key (trusted type):
+$ su -c 'keyctl pipe `keyctl search @u trusted kmk-trusted` > /etc/keys/kmk-trusted.blob'
+
+# or (user type):
+$ su -c 'keyctl pipe `keyctl search @u user kmk-user` > /etc/keys/kmk-user.blob'
+
+# A useful feature of trusted keys is that it is possible to prevent their
+# unsealing at later time by providing the parameter 'pcrlock=<pcrnum>' when
+# loading it, which causes the PCR #<pcrnum> to be extended with a random value.
+# Actually, the <pcrnum> variable is set to '11' to let users experiment with
+# this feature by using a register that is never extended during the boot,
+# making the re-sealing not necessary. In the future, the kernel master key will
+# be sealed to the PCR #14 which is extended, according to the TrustedGRUB
+# documentation[1], to the measure of the kernel and the initial ramdisk.
+
+# The kernel master key path name and type can be set in one of the following
+# ways (specified in the order in which variables are overwritten):
+
+1) use default values:
+--------------------------------------------------------------------------
+MULTIKERNELMODE="NO"
+MASTERKEYTYPE="trusted"
+MASTERKEY="/etc/keys/kmk-${MASTERKEYTYPE}.blob"
+--------------------------------------------------------------------------
+
+2) create the configuration file '/etc/sysconfig/masterkey' to override the
+value of one or all variables;
+
+3) specify these parameters in the kernel command line:
+- masterkey=</kernel/master/key/path>, to override the MASTERKEY variable;
+- masterkeytype=<kernel-master-key-type>, to override the MASTERKEYTYPE variable.
+
+# The variable MULTIKERNELMODE has been introduced to support multi boot
+# configurations, where a trusted/user key is tied to a specific kernel and
+# initial ramdisk. In this case, setting MULTIKERNELMODE to 'YES' will cause the
+# kernel version to be added to the default masterkey path name, so that the
+# MASTERKEY variable should not be overridden each time a different kernel is
+# chosen. The default value of MASTERKEY will be equal to:
+--------------------------------------------------------------------------
+MASTERKEY="/etc/keys/kmk-${MASTERKEYTYPE}-$(uname -r).blob"
+--------------------------------------------------------------------------
+
+# The masterkey path name also depends on the value of MASTERKEYTYPE, as reported
+# in the default values for defined variables. For example, if only MASTERKEYTYPE
+# is overridden by setting it to 'user' in the configuration file or from the
+# kernel command line, the value of MASTERKEY will be:
+--------------------------------------------------------------------------
+MASTERKEY="/etc/keys/kmk-user.blob"
+--------------------------------------------------------------------------
+
+
+[1] https://projects.sirrix.com/trac/trustedgrub/

modules.d/97masterkey/masterkey.sh

@@ -0,0 +1,75 @@
+#!/bin/sh
+# -*- mode: shell-script; indent-tabs-mode: nil; sh-basic-offset: 4; -*-
+# ex: ts=8 sw=4 sts=4 et filetype=sh
+
+# Licensed under the GPLv2
+#
+# Copyright (C) 2011 Politecnico di Torino, Italy
+#                    TORSEC group -- http://security.polito.it
+# Roberto Sassu <roberto.sassu@polito.it>
+
+MASTERKEYSCONFIG="${NEWROOT}/etc/sysconfig/masterkey"
+MULTIKERNELMODE="NO"
+PCRLOCKNUM=11
+
+load_masterkey()
+{
+    # read the configuration from the config file
+    [ -f "${MASTERKEYSCONFIG}" ] && \
+        . ${MASTERKEYSCONFIG}
+
+    # override the kernel master key path name from the 'masterkey=' parameter
+    # in the kernel command line
+    MASTERKEYARG=$(getarg masterkey=)
+    [ $? -eq 0 ] && \
+        MASTERKEY=${MASTERKEYARG}
+
+    # override the kernel master key type from the 'masterkeytype=' parameter
+    # in the kernel command line
+    MASTERKEYTYPEARG=$(getarg masterkeytype=)
+    [ $? -eq 0 ] && \
+        MASTERKEYTYPE=${MASTERKEYTYPEARG}
+
+    # set default values
+    [ -z "${MASTERKEYTYPE}" ] && \
+        MASTERKEYTYPE="trusted"
+
+    if [ -z "${MASTERKEY}" ]; then
+        # append the kernel version to the default masterkey path name
+        # if MULTIKERNELMODE is set to YES
+        if [ "${MULTIKERNELMODE}" = "YES" ]; then
+            MASTERKEY="/etc/keys/kmk-${MASTERKEYTYPE}-$(uname -r).blob"
+        else
+            MASTERKEY="/etc/keys/kmk-${MASTERKEYTYPE}.blob"
+        fi
+    fi
+
+    # set the kernel master key path name
+    MASTERKEYPATH="${NEWROOT}${MASTERKEY}"
+
+    # check for kernel master key's existence
+    if [ ! -f "${MASTERKEYPATH}" ]; then
+        if [ "${RD_DEBUG}" = "yes" ]; then
+            info "masterkey: kernel master key file not found: ${MASTERKEYPATH}"
+        fi
+        return 1
+    fi
+
+    # read the kernel master key blob
+    KEYBLOB=$(cat ${MASTERKEYPATH})
+
+    # add the 'load' prefix if the key type is 'trusted'
+    [ "${MASTERKEYTYPE}" = "trusted" ] && \
+        KEYBLOB="load ${KEYBLOB} pcrlock=${PCRLOCKNUM}"
+
+    # load the kernel master key
+    info "Loading the kernel master key"
+    keyctl add "${MASTERKEYTYPE}" "kmk-${MASTERKEYTYPE}" "${KEYBLOB}" @u >/dev/null || {
+        info "masterkey: failed to load the kernel master key: kmk-${MASTERKEYTYPE}";
+        return 1;
+    }
+
+    return 0
+}
+
+load_masterkey

modules.d/97masterkey/module-setup.sh

@@ -0,0 +1,25 @@
+#!/bin/bash
+# -*- mode: shell-script; indent-tabs-mode: nil; sh-basic-offset: 4; -*-
+# ex: ts=8 sw=4 sts=4 et filetype=sh
+
+check() {
+    [ "$1" = "-h" ] && {
+        [ -x "/bin/keyctl" ] || return 1
+    }
+
+    return 0
+}
+
+depends() {
+    return 0
+}
+
+installkernel() {
+    instmods trusted encrypted
+}
+
+install() {
+    inst keyctl
+    inst uname
+    inst_hook pre-pivot 60 "$moddir/masterkey.sh"
+}