NOTE: this page was created while the patch was in development and served to record some information of interest to the developers. Some of the information is outdated.

====== Address Space Layout Randomization (ASLR) ======

Support for Address Space Layout Randomization was added in %%FreeBSD%% HEAD (13-CURRENT) in [[https://svnweb.freebsd.org/changeset/base/343964|base r343964]]. It is enabled  by default in 14-CURRENT for 64bit architectures, as of [[https://cgit.freebsd.org/src/commit/sys/kern/imgact_elf.c?id=b014e0f15bc73d80ef49b64fd1f8c29f469467cb|base commit b014e0f15bc7]].  It is enabled by default for 64-bit architectures in %%FreeBSD%% 13.2 and later releases.

===== Architectures =====

ASLR is enabled on a per-ABI basis, and is supported on all architectures as of 72091bb39382abba0d71dc23738684bfb4bc2574.

===== Configuration =====

Global controls :

  * ''%%kern.elf{32,64}.aslr.enable%%'' - Enable address map randomization (Default: 1 for 64bit architectures, 0 for 32bit architectures)
  * ''%%kern.elf{32,64}.aslr.pie_enable%%'' - Enable ASLR for Position-Independent Executables (PIE) binaries (Default: 1 for 64bit architectures, 0 for 32bit architectures)
  * ''%%kern.elf{32,64}.aslr.honor_sbrk%%'' - Assume sbrk is used (Default: 0)
  * ''%%vm.cluster_anon%%'' - Cluster anonymous mappings (Default: 1)

Per-process and per-image controls:

  * procctl(2) adds PROC_ASLR_CTL / PROC_ASLR_STATUS
  * NT_FREEBSD_FCTL_ASLR_DISABLE feature control note bit makes it possible to force ASLR off for the given binary. A tool to edit the feature control note is in development.

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{{tag>Security}}