Increase _FORTIFY_SOURCE to level 3

Signed-off-by: Allan McRae allan@archlinux.org

rfcs/0017-increase-fortification-level.rst

+===================================
+Increase _FORTIFY_SOURCE level to 3
+===================================
+
+- Date proposed: 2023-01-05
+- RFC MR: https://gitlab.archlinux.org/archlinux/rfcs/-/merge_requests/0017
+
+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 distribtion 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.