Userspace system daemon to enable security levels for Thunderbolt™ on GNU/Linux®.
Thunderbolt™ is the brand name of a hardware interface developed by Intel® that allows the connection of external peripherals to a computer.
Devices connected via Thunderbolt can be DMA masters and thus read system memory without interference of the operating system (or even the CPU). Version 3 of the interface introduced 5 different security levels, in order to mitigate the aforementioned security risk that connected devices pose to the system. The security level is set by the system firmware.
The five security levels are:
none: Security disabled, all devices will fully functional on connect.
dponly: Only pass the display-port stream through to the connected device.
user: Connected devices need to be manually authorized by the user.
secure: As 'user', but also challenge the device with a secret key to verify its identity.
usbonly: One PCIe tunnel is created to a usb controller in a thunderbolt dock; no other downstream PCIe tunnels are authorized (needs 4.17 kernel and recent hardware).
The Linux kernel, starting with version 4.13, provides an interface via sysfs that enables userspace query the security level, the status of connected devices and, most importantly, to authorize devices, if the security level demands it.
The core of bolt is a system daemon (
boltd) that interfaces with
sysfs and exposes devices via D-Bus to clients. It also has a database
of previously authorized devices (and their keys) and will, depending
on the policy set for the individual devices, automatically authorize
newly connected devices without user interaction. The daemon supports
syncing the devices database with the pre-boot access control list
firmware feature. It also adapts its behavior when iommu support is
boltctl command line can be used to manage thunderbolt devices
boltd. It can list devices, monitor changes and initiate
authorization of devices.
The meson build system is used to configure and compile bolt.
meson build # configure bolt, use build as buildir
ninja -C build # compile it
ninja -C build test # run the tests