Project:Hardened musl

Hardened musl
Description	This subproject aims to port the hardened tool chain to musl based systems for a variety of architectures. The project treats musl as an alternative to glibc and uClibc, and not necessarily as "embedded".
Project email	gentoo-musl@lists.gentoo.org
IRC channel	#gentoo-hardened
Lead(s)	Anthony G. Basile (blueness) Developer No lead election date set
Member(s)
Subproject(s) (and inherited member(s))	(none)
Parent Project	Gentoo Hardened
Project listing

The Hardened musl subproject has a goal similar to its sister subproject, Hardened uClibc, but with the intention of using musl to replace glibc as the system's "standard C library," or "libc" for short. A system's libc forms an integral part of the toolchain, but unlike the other components, it remains a runtime dependency of nearly every dynamically linked object in the system, or becomes incorporated into statically linked executables. For embedded systems, the size and speed of your libc become important issues which are better addressed by libc's designed with that purpose in mind. uClibc addresses at least the size issue by being very configurable, so any unneeded code can be turned off. Whether a function is required by POSIX standards or not doesn't matter if you are not using it for some targetted application. musl takes a different approach: it is written with static linking in mind, but also with fast dynamic linking capabilities, while remaining close to standards and conscious of security issues. However, unlike uClibc, it is not configurable. How glibc, uClibc and musl compare on the various points of interest is complex and something that will probably be debated forever. The musl team does provide a table of C/POSIX standard library implementations for Linux that you can browse. Since there are different needs for different folks, in Gentoo we are not afraid to target anything and everything: all arches, all libc's, hardened/vanilla userland, hardened/vanilla Linux kernel, and even different kernels.

musl's completeness, including a robust implementation of POSIX threads, means that we can include all of Gentoo's Hardened toolchain goodies without any problems:

• Stack Smashing Protection (SSP), which requires threads but doesn't work with the old NPTL or LinuxThreads that uClibc provides.
• Position Independent Execution (PIE).
• Bind now and relro, linker hardening to protect the global offset table.

These are augmented by the kernel hardening, especially PaX's enhanced address space layout randomization (ASLR).

This subproject aims to treat musl more as a drop in alternative to glibc, and not necessarily as "embedded". This is not at the exclusion of the concerns of embedded systems, but rather to make our userland tarballs as flexible as possible. They can be used as development environments for native compiling on native hardware, starting points to build server or desktop systems, or they can be stripped down to just the essential apps for whatever purpose. The stages are not "embedded" in the sense that they use busybox as their "Swiss Army Knife" of common UNIX utilities. While not excluding this possibility, we aim at making most (all?) of Gentoo's packages both hardened and musl compatible.

Goals

The project goals can be best summarized by the following chart:

Arch	Subarchs	Tool Chain Hardening	Status	Downloads
amd64	Generic	Yes	Development	Desktop stage3-amd64-musl-{hardened,vanilla}
arm	armv7a-hardfp	Yes	Development	stage3-armv7a_hardfp-musl-{hardened,vanilla}
mips	mips32r2	No	NA	Not Yet
mips	mipsel3	No	Development	stage3-mipsel3-musl-vanilla
ppc	classic	No	Development	stage3-ppc-musl-vanilla
x86	i686	No	Development	stage3-i686-musl-vanilla

Working with musl

Unlike the situation with uClibc, where pretty much every package in the Gentoo portage tree "just builds," musl's adherence to standards means that many packages which deviate from those standards, primarily POSIX, need some patching. Most of this is minor, like the location of header files, but some is more substantial. So we maintain the musl overlay to house those patches, and this overlay must be added to the stage3's to be able to update and maintain them. Here's how:

0) Get your chroot ready as you would on any other stage3. See the Handbook.

1) Set up your favorite GENTOO_MIRRORS and sync-uri and sync the main ebuild repository. Obviously replace 192.168.3.1 with your servers of choice:

root #echo GENTOO_MIRRORS=ftp://192.168.3.1/pub/gentoo >> /etc/portage/make.conf

root #sed -i "/^sync-uri/d" /etc/portage/repos.conf/gentoo.conf

root #echo "sync-uri = rsync://192.168.3.1/portage" >> /etc/portage/repos.conf/gentoo.conf

root #emerge --sync

2) Set up the nameserver for DNS resolution:

root #echo nameserver 192.168.3.1 >> /etc/resolv.conf

3) We need to get git in order to add the overlay. Unfortunately, right now we can't build git with gnupg support:

root #echo "dev-vcs/git -gpg" >> /etc/portage/package.use

root #emerge --ask app-portage/layman dev-vcs/git

4) Let's add the overlay.

root #layman -L

root #layman -a musl

5) Okay now we can update. If we tried to update without the overlay, we get a bunch of downgrades to ebuilds that are slightly broken on musl and will not build.

root #emerge -uvNDq @world

6) In the future, update both the portage tree and the overlay before repeating step 5.

root #emerge --sync

root #layman -S

root #emerge -uvNDq @world

Contributors

The following people are or have contributed to the project:

Contributor	Email	Still active?
Felix Janda	felix.janda@posteo.de	Yes

Participation

To participate in the Hardened musl project join the mailing list at gentoo-musl@lists.gentoo.org and visit our IRC channel at #gentoo-hardened on Freenode.

See also

• Bluedragon - A hardened musl XFCE desktop.