Increase _FORTIFY_SOURCE level to 3

Summary

Adjust packaging CFLAGS from -D_FORTIFY_SOURCE=2 to -D_FORTIFY_SOURCE=3 for better fortification coverage

Motivation

For a long time, we have been using -D_FORTIFY_SOURCE=2 in our build flags to detect C memory management problems at build time. Recently, glibc (2.34) added _FORTIFY_SOURCE=3 to add extra checking. This has been supported in clang for some time, and is now available in GCC with the release of version 12.

The gains are enhanced buffer size detection and better fortification coverage.

A study [1] showed level 3 improved fortification coverage by nearly 4 times on average. Extreme examples include the Bash shell going from roughly 3.4% coverage with level 2 to 47% with level 3. Similarly, sudo went from 1.3% to 49.57%.

[1] https://developers.redhat.com/articles/2022/09/17/gccs-new-fortification-level#2__better_fortification_coverage

Specification

CFLAGS in the distribution packaging makepkg.conf would change from -D_FORTIFY_SOURCE=2 to -D_FORTIFY_SOURCE=3.

Some applications use malloc_usable_size (despite the glibc manual stating it is for diagnostic purposes only). This is currently incompatible with _FORTIFY_SOURCE=3, so these packages will need to continue using level 2 by modifying C{,XX}FLAGS in the PKGBUILD. A TODO list will be created for all such packages on adoption of this proposal.

Drawbacks

Some claims of performance overhead have been made, but these are likely overblown [2]. Most of the checks are at compile time, and this change is being adopted by OpenSUSE, Fedora and Gentoo (in their hardened profile).

[2] https://siddhesh.in/posts/fortify-source-3-performance.html

Unresolved Questions

None.

Alternatives Considered

None.