The API/ABI for the LibreSSL 2.1.x series is now fixed, so we can safely
enable libtls it by default. This is useful for new OpenNTPD and
OpenSMTPD releases as well.
ok deraadt@ beck@ sthen@
Where available, enable stack smashing protection, fortify source,
no-strict-overflow, and read only relocations.
Many Linux distributions automatically enable most of these options.
They are no brainers. The difference introduced here is in asking for a
few more aggressive options. An option to disable the more aggressive
options is provided (--disable-hardening). When set, configure will fall
back to the default CFLAGS on the system - in many cases that will still
be hardened. There is no point in going further than that.
Options enabled are:
-fstack-protector-strong is a relatively new GCC-4.9 feature that is
supposed to give a better balance between performance and protection.
-all is considered too aggressive, but was used in Chromium and other
security critical systems until -strong became available. Follow their
lead and use -strong when possible. clang 6.0 supports -all but not
-strong.
_FORTIFY_SOURCE replaces certain unsafe C str* and mem* functions with
more robust equivalents when the compiler can determine the length of
the buffers involved.
-fno-strict-overflow instructs GCC to not make optimizations based on
the assumption that signed arithmetic will wrap around on overflow (e.g.
(short)0x7FFF + 1 == 0). This prevents the optimizer from doing some
unexpected things. Further improvements should trap signed overflows and
reduce the use of signed to refer to naturally unsigned quantities.
I did not set -fPIE (position independent executables). The critical
function of Open/LibreSSL is as a library, not an executable.
Tested on Ubuntu Linux 14.04.1 LTS, OS X 10.10.1 with "make check".
The code added to m4/ is GPLv3 but con
Signed-off-by: Jim Barlow <jim@purplerock.ca>
