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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.

boltd - the system daemon

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 detected.

boltctl - command line client

The boltctl command line can be used to manage thunderbolt devices via 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

See INSTALL for more information, BUGS for how to file issues and HACKING how to contribute.