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. Trying The Configurable 45 Watt TDP With AMD's A10-7800 / A6-7400K
  2. Sumo's Omni Gets Reloaded
  3. AMD A10-7800 & A6-7400K APUs Run Great On Linux
  4. Radeon Gallium3D Is Running Increasingly Well Against AMD's Catalyst Driver
Latest Linux Articles
  1. AMD's RadeonSI Driver Sped Up A Lot This Summer
  2. Intel's Latest Linux Graphics Code Competes Against OS X 10.9
  3. Intel Sandy Bridge Gets A Surprise Boost From Linux 3.17
  4. Open-Source Radeon Graphics Have Some Improvements On Linux 3.17
Latest Linux News
  1. The Widely-Criticized New Commercial Linux Distro Is Now On Kickstarter
  2. CUDA 6.5 Is Doing Great For Blender
  3. Wayland & Weston 1.6 Alpha Released
  4. Nouveau Gets Improved Re-Clocking Handling For Select GPUs
  5. A New First-Person Mystery Game Might Be Coming To Linux
  6. Patch By Patch, LLVM Clang Gets Better At Building The Linux Kernel
  7. VC4 Gallium3D Driver Now Handles X With GLAMOR
  8. Opera 25 Development Release For Linux
  9. Steam Now Supports VA-API For In-Home Game Streaming
  10. GNOME 3.14 Beta Released
Latest Forum Discussions
  1. Systemd 216 Piles On More Features, Aims For New User-Space VT
  2. OSS radeon driver for A10-7850K (Kaveri)
  3. Btrfs Gets Talked Up, Googler Encourages You To Try Btrfs
  4. American Citizens running AMOK for food stamps
  5. What Linux Distribution Should Be Benchmarked The Most?
  6. Company I work for is looking to contribute to Open Source projects... but wrongly?
  7. Microsoft vs. Campaign
  8. Updated and Optimized Ubuntu Free Graphics Drivers