[CFT] ASLR and PIE on amd64

Hey All, First off, I hope that even as a non-committer, it's okay that I post a call for testing. If not, please excuse my newbishness in this process. This is my first time submitting a major patch upstream to FreeBSD. Over the past few months, I've had the opportunity and pleasure to enhance existing patches to FreeBSD that implement a common exploit mitigation technology called Address Space Layout Randomization (ASLR) along with support for Position Independent Executables (PIE). ASLR+PIE has been a long-requested feature by many people I've met on IRC. I've submitted my patch to PR kernel/181497. I'm currently in the process of adding PIE support to certain high-visibility applications in base (mainly network daemons). I've added a make.conf knob that's default to enabled (WITH_PIE=1). An application has to also explicitly support PIE as well by defining CAN_PIE in the Makefile prior to including bsd.prog.mk. After I get a decent amount of applications enabled with PIE support, I'll submit one last patch. The following sysctl's can be set with a kernel compiled with the PAX_ASLR option: security.pax.aslr.status: 1 security.pax.aslr.debug: 0 security.pax.aslr.mmap_len: 16 security.pax.aslr.stack_len: 12 security.pax.aslr.exec_len: 12 The security.pax.aslr.status sysctl enables and disables the ASLR system as a whole. The debug sysctl gives debugging output. The mmap_len sysctl tells the ASLR system how many bits to randomize with mmap() is called. The stack_len sysctl tells the ASLR system how many bits to randomize in the stack. The exec_len sysctl tells the ASLR system how many bits to randomize the execbase (this controls PIE). These sysctls can be set as a per-jail basis. If you have an application which doesn't support ASLR, yet you want ASLR enabled for everything else, you can simply place that misbehaving application in a jail with only that jail's ASLR settings turned off. Please let me know how your testing goes. I'm giving a presentation at BSDCan regarding this. If you want to keep tabs on my bleeding-edge development process, please follow my progress on GitHub: https://github.com/lattera/freebsd (branch: soldierx/lattera/aslr). Thank you very much, Shawn Webb