Kernel/Deblobbing

Resources

From Wikipedia: A binary blob is a closed-source binary-only piece of software without publicly available source code. Since 1996, Linux kernel includes an increasing amount of binary blobs to handle devices with closed-sources firmware only (and among these devices, those without technical documentation which would authorize free firmware development for them). Proprietary software always introduces freedom, security, or privacy concerns.

Deblobbing is the operation which removes binary blobs from source code to get a completely blob-free kernel. This is done with two shell scripts written by Brian Brazil, Jeff Moe, and Alexandre Oliva, named deblob-check and deblob-<version>, where <version> represents the kernel revision. A third script which is for Linux tarballs, deblob-main, is not used here. See the scripts README to get information about them.

Those scripts are provided by the Free Software Foundation Latin America, for each kernel revision. FSFLA mainly provides Linux-libre distribution.

Once deblobed the kernel is compiled as usual. Deblobbing kernel obviously means that devices that exclusively support proprietary firmware cannot be used. Generally this includes all new Intel wireless cards. Nvidia graphic cards will only use the nouveau open source driver.

See below how to get a list of removed blobs without kernel compilation.

Deblobbing rt-sources

For sys-kernel/rt-sources, set the USE flag deblob in /etc/portage/make.conf, sources will be automatically deblobed after being emerged.

Deblobbing gentoo-sources (or any other sources)

Note
Starting with kernel version 4.14, the entire firmware tree has been removed, rendering deblobbing unnecessary for new kernel versions. However, the Linux-libre patches go beyond deblobbing by removing certain functionalities (e.g. firmware loaders) from the kernel. Therefore, these patches remain valuable for users who prioritize software freedom over other considerations, such as security updates for CPU vulnerabilities.

Emerging sources

Note
linux-6.8.1-gentoo is used in the following example.

Emerge Gentoo sources:

root #emerge --ask sys-kernel/gentoo-sources

Then set /usr/src/linux symlink to the emerged sources if symlink USE flag is not set for Gentoo sources:

First get the list of available sources:

root #eselect kernel list

[1] linux-6.7.8-gentoo *
[2] linux-6.8.1-gentoo
etc.

… then choose the right ones:

root #eselect kernel set linux-6.8.1-gentoo

Then change directory to /usr/src/linux:

root #cd /usr/src/linux

Downloading deblob scripts

Scripts are on Linux-libre server. First make some vars to simplify lines to be entered:

version will contain sources version and is the only one to be adapted, a minor version number is not mandatory;
main will be generated, containing version without minor revision if needed, 6.8 for 6.8.1;
(If there is a release candidate string, 6.9-rc7 for example, enter main by hand —there is usually no rc string with gentoo-sources.)
url will contain downloading URL.

Making the vars:

root #

version=6.8.1

root #

if [ `echo $version | tr -cd '.' | wc -c` == 2 ]; then main=`echo ${version%.*}`; else main=$version; fi

root #

url=https://linux-libre.fsfla.org/pub/linux-libre/releases/

Downloading:

root #

wget $url$version-gnu/deblob-$main

root #

wget $url$version-gnu/deblob-$main.sign

root #

wget $url$version-gnu/deblob-check

root #

wget $url$version-gnu/deblob-check.sign

Make the scripts executable by root only:

root #chmod 744 deblob-$main deblob-check

Verifying signatures

First import or update the Linux-libre server key:

root #gpg --keyserver keys.gnupg.net --recv-key BCB7CF877E7D47A7

Then verify the signatures:

root #

gpg --verify deblob-$main.sign deblob-$main

root #

gpg --verify deblob-check.sign deblob-check

Note
For each verification this warning is usual, because server's key was imported but not trusted:

gpg: WARNING: This key is not certified with a trusted signature!
gpg:          There is no indication that the signature belongs to the owner.

The important output is Good signature for each script.

Python version

Deblob scripts use the Python 3.8 interpreter. Emerge it:

root #emerge --ask --noreplace --oneshot dev-lang/python:3.8

Deblob command

Deblobbing can now be started (remember the main var):

root #PYTHON="python3.8" ./deblob-$main

During the operation, which may be long, all deblobbing information is displayed. After kernel compilation -gnu suffix will be appended to it's name, 6.8.1-gentoo-gnu in this example.

List of removed blobs

To get the list of removed blobs with their kernel symbol names, redirect the deblob command output to a file:

root #PYTHON="python3.8" ./deblob-$main > /path/to/file/deblob-$version.log

As kernel sources can be re-emerged after being deblobed, this is a convenient way, without kernel compilation, to investigate if targeted hardware should work without binary blobs.

External resources

The Binary blob Wikipedia article