Hardened linux
Why Linux-Hardened Kernel?
You may want to get a more security focused kernel, custom private syscalls (only if you compile it for yourself and is not publicly shown), apply Grsecurity/KSPP/GrapheneOS kernel hardening suggestions and remove attack surface from the kernel (with the kernel-hardening-checker APK package).
Developing Linux-hardened kernel with hardened patch
/etc/apk/repositories
Make a custom linux kernel using this guide [1]. Once you have setup the linux kernel from there, in your current directory ($YOUR_WORK_DIR/aports/main/linux-lts), gather linux hardened patches via these two CLI commands (Replace "$VERSION" with the current latest version in the releases):
$ wget https://github.com/anthraxx/linux-hardened/releases/download/v$VERSION-hardened1/linux-hardened-v$VERSION-hardened1.patch 0006-linux-hardened-v$VERSION-hardened1.patch
$ wget https://github.com/anthraxx/linux-hardened/releases/download/v$VERSION-hardened1/linux-hardened-v$VERSION-hardened1.patch.sig 0007-linux-hardened-v$VERSION-hardened1.patch.sig
In the "APKBUILD" file, change this "source" line to this:
Contents of ./APKBUILD
In "APKBUILD" file again, change "pkgver" and "pkgrel" to the same as the releases patch file's "$VERSION"
Contents of ./APKBUILD
You may change the pkg name's flavor (if you do that, replace all words "lts" with your preferred flavor name (for example "hardened"), and, for example, change the file lts.x86_64.config to hardened.x86_64.config), but for this wiki it'll just be LTS
Contents of ./APKBUILD
There is some need to remove "-hardened1" in the patch file (not the sig file):
Contents of ./0006-linux-hardened-v$VERSION-hardened1.patch
EXTRAVERSION" naming ("-hardened1") after it, or installing the package "kernel-hooks" would not do anything, as this "EXTRAVERSION" is not necessary. ("kernel-hooks" apk package is necessary to make a secureboot EFISTUB) [2].
Developing Linux-hardened kernel with hardened config
OPTIONAL: Before compiling the kernel, in the Alpine Linux custom kernel guide [1], you must do some kernel module configurations (do this by abuild -rK for a few seconds, then exiting by Ctrl-C, and then go to src/linux-$VERSION/, download this Arch_hardened_x86_64.config:
$ doas apk add zstd tar $ mkdir arch $ cd arch $ wget -O linux-hardened-headers.pkg.tar.zst https://archlinux.org/packages/extra/x86_64/linux-hardened-headers/download/ $ tar -xvf linux-hardened-headers.pkg.tar.zst $ cd .. && cp ./arch/usr/src/linux-hardened/.config ./Arch_hardened_x86_64.config $ mv ./arch ../../
And do make menuconfig, and select "load", and input the downloaded .config file's name: Arch_hardened_x86_64.config, preferably shorten the amount of kernel modules in the .config files where possible, to reduce compilation times. You may use the just-downloaded Arch_hardened_x86_64.config as a base for configuration simplicity sake. (Use the apk package "kernel-hardening-checker" for configuring .config file as securely as possible, as it contains some grsecurity and kspp kernel configuration suggestions and more.)
Arch_hardened_x86_64.config needs some modification, in menuconfig, general setup -> kernel compression mode, set it to GZIP.
kernel-hardening-checker, do mkdir kernel-hardening-checker && cd kernel-hardening-checker, and you should acquire THREE files in the current directory: one with sysctl parameters ($ doas sysctl -a > sysctl.conf"sysctl.conf"), one with boot parameters ($ cat /proc/version > ./cmdline.conf"cmdline.conf"), and the .config file ("Arch_hardened_x86_64.config"). And then run with this CLI command: $ kernel-hardening-checker -c ./Arch_hardened_x86_64.config -s ./sysctl.conf -l ./cmdline.conf
Afterwards do
cd .. && mv ./kernel-hardening-checker $YOUR_WORK_DIR/aports/main/linux-lts so you dont lose this directory when it finishes compiling the kernel (it deletes the src directory).cp $YOUR_WORK_DIR/aports/main/linux-lts/src/linux-$VERSION/Arch_hardened_x86_64.config $YOUR_WORK_DIR/aports/main/linux-lts/lts.x86_64.config when finished configuring .config kernel file.$YOUR_WORK_DIR/aports/main/linux-lts/virt.x86_64.config is the kernel for virtualization (QEMU, Xen), do not customize this for this wiki.After applying this, you may do cd $YOUR_WORK_DIR/aports/main/linux-lts and abuild checksum && abuild -r to start compiling the kernel.
When the compile has successfully completed, you should see ~/packages/main/$ARCH/linux-lts-$VERSION.apk and may install by apk add linux-lts=$VERSION(make sure to do apk update, and that /etc/apk/repositories contains $YOUR_USERS_HOME_DIR/packages/main.
External Links:
Custom Kernel (AlpineWiki):
- Custom_Kernel [1]
EFIStub (Secure Boot) (AlpineWiki):
- UEFI_Secure_Boot [2]