Introduction:
chkboot is a set of scripts that are meant to be run on a system with an encrypted disk drive. Due to the nature of disk encryption, in order to get the operating system to boot, there needs to be a portion of it which remains un-encrypted. These scripts check that those files have not changed between reboots. Since the scripts and the data they generate are stored on the encrypted part of the disk, any attempts to modify the boot partition between reboots will be detected.
Limitations
Be aware that chkboot can not protect you against:
- a trojan hiding in your BIOS
- rootkits that mimmick the old files
Description
chkboot: When run as root, this generates sha256sum hashes of each boot file
and the MBR of the boot partition if it exists, then compares the values of
these hashes against previously generated hashes if they exist, and any files
that don't match get added to a list. A timestamped log of all files that have
had changes made to them is kept, but the short term list meant to alert the
user is erased the next time chkboot is run.
chkboot-check: This file can be run by anyone who can view /var/lib/chkboot,
and will display a warning and the list of changed files if any were detected last
time chkboot was run.
chkboot.conf: Contains settings for your configuration, including which
alert types will be used. Alert types are currently on shell login via
'/etc/profile.d' and in the vterm header by modifying '/etc/issue'
INITCPIO SUPPORT: If your system uses initcpio, add 'chkboot' to the end of
your modules array to have chkboot run automatically when you upgrade Linux.
SYSTEMD SUPPORT: If your system uses systemd, you should enable the chkboot
service to have your boot partitioned checked every time your system starts.
Installation
The basic components can be installed as shown below
make install
To install initcpio components:
make install-initcpio
To install systemd components:
make install-systemd
Manual Installation
Everything should be installed as shown below
install -D -m644 chkboot/chkboot.conf /etc/default/chkboot.conf
install -D -m755 chkboot/chkboot /usr/bin/chkboot
install -D -m755 chkboot/chkboot-check /usr/bin/chkboot-check
install -D -m755 chkboot/chkboot-profilealert.sh /etc/profile.d/chkboot-profilealert.sh
To make chkboot run on startup on BSD-style init-based systems (e.g. Debian,
Ubuntu), add the following line to /etc/rc.local:
/usr/bin/chkboot &
REQUIRES INITCPIO:
Add chkboot to the end of the 'HOOKS' array in /etc/mkinitcpio.conf
install -D -m644 chkboot/chkboot-initcpio /usr/lib/initcpio/install/chkboot
REQUIRES SYSTEMD
Run systemctl --system daemon-reload and then systemctl enable chkboot
OPTIONAL:
chkboot-bootcheck can be installed elsewhere and added to the startup sequence
with another system:
install -D -m644 chkboot/chkboot.service /usr/lib/systemd/system/chkboot.service
install -D -m755 chkboot/chkboot-bootcheck /usr/lib/systemd/scripts/chkboot-bootcheck
Credits
Author: Ju (ju at heisec dot de)
chkboot originally appeared in an article titled "Boot-Sicherung" in [c't magazin's March 2012 issue] 1. The original author is Juergen Schmidt, ju at heisec.de. The original source code can be found either at the first commit of this repository, or at the [original URL] 2.
Additional authors: Inhies (https://github.com/inhies/) Prurigro (https://github.com/prurigro/)