1. Computers
  2. Display Drivers
  3. Graphics Cards
  4. Memory
  5. Motherboards
  6. Processors
  7. Software
  8. Storage
  9. Operating Systems


Facebook RSS Twitter Twitter Google Plus


Phoronix Test Suite

OpenBenchmarking.org

Defeating Secure Boot With Linux Kexec

Linux Kernel

Published on 04 December 2013 09:58 AM EST
Written by Michael Larabel in Linux Kernel
29 Comments

Matthew Garrett has written an insightful blog post about security issues pertaining to the Linux kernel's kexec functionality that could defeat any security benefits provided by Secure Boot. Using kexec could even allow you to boot a Windows kernel.

Matthew has long been dealing with UEFI/SecureBoot issues and his latest blog post is entitled Subverting security with kexec. Garrett noted, "The beauty of this approach is that it doesn't rely on any kernel bugs - it's using kernel functionality that was explicitly designed to let you do this kind of thing (ie, run arbitrary code in ring 0). There's not really any way to fix it beyond adding a new system call that has rather tighter restrictions on the binaries that can be loaded. If you're using signed modules but still permit kexec, you're not really adding any additional security. But that's not the most interesting way to use kexec. If you can load arbitrary code into the kernel, you can load anything. Including, say, the Windows kernel. ReactOS provides a bootloader that's able to boot the Windows 2003 kernel, and it shouldn't be too difficult for a sufficiently enterprising individual to work out how to get Windows 8 booting. Things are a little trickier on UEFI - you need to tell the firmware which virtual -> physical map to use, and you can only do it once. If Linux has already done that, it's going to be difficult to set up a different map for Windows. Thankfully, there's an easy workaround. Just boot with the 'noefi' kernel argument and the kernel will skip UEFI setup, letting you set up your own map."

The post is interesting and certainly worth reading in full. For those wanting some background information on Kexec, stop by Wikipedia.

About The Author
Michael Larabel is the principal author of Phoronix.com and founded the web-site in 2004 with a focus on enriching the Linux hardware experience and being the largest web-site devoted to Linux hardware reviews, particularly for products relevant to Linux gamers and enthusiasts but also commonly reviewing servers/workstations and embedded Linux devices. Michael has written more than 10,000 articles covering the state of Linux hardware support, Linux performance, graphics hardware drivers, and other topics. Michael is also the lead developer of the Phoronix Test Suite, Phoromatic, and OpenBenchmarking.org automated testing software. He can be followed via and or contacted via .
Latest Linux Hardware Reviews
  1. Rosewill RS-MI-01: An Ultra Low-Cost Mini-ITX Chassis
  2. D-Link DCS-2330L HD Wireless Network Camera
  3. Gigabyte AM1M-S2H
  4. AMD's New Athlon/Semprons Give Old Phenom CPUs A Big Run For The Money
Latest Linux Articles
  1. AMD Catalyst 14.4 On Linux With Radeon R3 APU Graphics
  2. Red Hat Enterprise Linux 7.0 RC Benchmarks
  3. AMD Catalyst 14.4 Brings Few Linux Performance Improvements
  4. The Performance Of Fedora 20 Updated
Latest Linux News
  1. R600 Gallium3D Lands Many OpenGL Fixes
  2. LLVMpipe Gallium3D Now Exposes GLSL 3.30
  3. NGINX 1.6 Brings SPDY 3.1 & Other New Features
  4. Linux Foundation Announces A Core Infrastructure Initiative
  5. More Steam Linux Tests/Benchmarks Might Be Coming
  6. NVIDIA's Amazing Single-Board ARM Computer Might Be Delayed
  7. Fedora 21 To Get A Playground, New Features
  8. PC-BSD Is Developing Its Own Desktop Environment
  9. Valve Is Bringing VOGL To Windows & Working On Regression Tests
  10. Canonical Is Taking Over Linux 3.13 Kernel Maintenance
  11. Google Web Designer Is Now Natively Available On Linux
  12. Ubuntu 14.10 Is Codenamed The Utopic Unicorn
Latest Forum Discussions
  1. Linux Kernel Developers Fed Up With Ridiculous Bugs In Systemd
  2. HTPC-upgrade advice: AMD Richland A8-7600 or Kaveri A10-6700T ???
  3. What Else Would You Like To See On Phoronix This Spring?
  4. The GNOME Foundation Is Running Short On Money
  5. The Most Amazing OpenGL Tech Demo In 64kb
  6. Announcing radeontop, a tool for viewing the GPU usage
  7. New card. Open source drivers only.
  8. Script for Fan Speed Control