LibreSSL in HardenedBSD base Part I 05 mar 2016 | Last updated: 05 mar 2016 19:51

With last week's OpenSSL vulnerabilities questions came up when LibreSSL would replace OpenSSL in FreeBSD base. This was picked up by the HardenedBSD developers and they asked me if I'd be interested in adding LibreSSL as alternative libcrypto/ssl in HardenedBSD. Well SURE I do! This post describes the early stages of this project.

LibreSSL in HardenedBSD base Part I

It seemed to be a way bigger thing than I thought, after the HardenedBSD announcement I got congratulations from many places. I can only see that as endorsement to make it happen!

The challenge

  1. Add LibreSSL as alternative provider of libcrypto and libssl in HardenedBSD
  2. Allow selecting LibreSSL or OpenSSL using /etc/src.conf

And so it begins

After setting up a VM with HardenedBSD 42 (based on FreeBSD 11) I branched the HardenedBSD playground source repository into hardened/current/libressl.

This branch I cloned to my HardenedBSD VM in /usr/src and is the starting point for the changes. I ran a full make buildworld to have a populated /usr/obj tree that I can hack on.

Then I added LibreSSL 2.3.2 (latest snapshot release for the upcoming OpenBSD 5.9) to the mix by extracting it into /usr/src/crypto/libressl (notice the nice relic from the previous Crypto Wars here, putting all crypto sources in a separate path makes it easier to distribute without the strong crypto).

By default LibreSSL portable builds with Cmake but that's not an option for the base system, so I added the latest Makefile from OpenBSD to the repository in /usr/src/secure/lib/libcrypto and /usr/src/secure/lib/libcrypto.

Beginner mistakes

I dove straight into /usr/src/share/Mk to edit files that were relevant to OpenSSL building. I started adding WITH_LIBRESSL and adding conditionals to disable OpenSSL when LibreSSL is selected. There's a big mistake in that aproach! The base system's Makefile's are littered with

.if ${MK_OPENSSL} == "no"
disabled code

My approach would set WITHOUT_OPENSSL and additionally set MK_OPENSSL=no effectively disabling OpenSSL, and that's NOT what we want!

The behaviour that is requested to leave the MK_OPENSSL knob function as is, and only alter the libraries that are used. To do so we should only want one knob to drive the behaviour of base. This is the magic knob in /etc/src.conf


That is all it should take to build with LibreSSL and without OpenSSL. Going forward, some more bits will have to be added.

  1. setting WITHOUT_OPENSSL= yes should still work as it does currently (although it is broken)
  2. setting WITH_LIBRESSL= yes and WITHOUT_OPENSSL= yes should build LibreSSL and not OpenSSL but NOT set MK_OPENSSL= no
  3. setting WITH_LIBRESSL= yes should behave as option 2.

Don't try the modified WITHOUT_OPENSSL behaviour just yet, it's not implemented!

Pick and choose

The LibreSSL tarball includes additional code that is in OpenBSD base but not found on other operating systems. We will need to add some of these to the build. This is where the port helps out, it uses Cmake to detect what needs to be added. Using cmake -LAH to generate CMakeCache.txt I get the following missing features

$ grep '^HAVE.*=$' CMakeCache.txt

We will have to add these to the makefile to allow LibreSSL to build.


When building LibreSSL (and OpenSSL as well), it will first build libcrypto and then libssl as the latter requires the former to build. So we start hacking in /usr/src/secure/lib/libcrypto

# $FreeBSD$

.if !"${WITH_LIBRESSL}" == "yes"

# content of the original Makefile

.include "Makefile.libressl"
.endif # ${MK_OPENSSL} != "no"

This isn't the cleanest way to do it, but makes merging changes from FreeBSD later on a lot easier. If WITH_LIBRESSL is defined, we simply jump to the modified copy of OpenBSD's Makefile which I named Makefile.libressl

The Makefile is largely OK but we need to add the compatibilty code from OpenBSD and set the paths correctly for make to find the source files. The file crypto/CMakeLists.txt is very helpful here.

The relevant changes from Makefile.libressl

OPENSSL_VER=    2.3.2
OPENSSL_DATE=   2016-01-28

LIBRESSL_SRC=   ${.CURDIR}/../../../crypto/libressl
SSL_SRC=        ${LIBRESSL_SRC}/ssl

CFLAGS+= -I${LIBRESSL_SRC}/include -I${LIBRESSL_SRC}/include/compat

# compat/
SRCS+=  explicit_bzero.c getentropy_freebsd.c reallocarray.c \
        timingsafe_bcmp.c timingsafe_memcmp.c

        CFLAGS+= -O0

And see there! It builds!


The modification to the default secure/lib/libssl/Makefile is done exactly like the libcrypto modification.

Again, very little change was required to make this work. Basically modifying the paths is all that was required to build libssl.

The relevant changes in Makefile.libressl


LIBRESSL_SRC=   ${.CURDIR}/../../../crypto/libressl
LSSL_SRC=        ${LIBRESSL_SRC}/ssl

.include <>
CFLAGS+= -Wall -Wundef
CFLAGS+= -I${LIBRESSL_SRC}/include -I${LIBRESSL_SRC}/include/compat
CFLAGS+= -I${LIBRESSL_SRC}/crypto -I${LIBRESSL_SRC}/crypto/evp

LIBADD= crypto


With these changes, libssl builds without problem.

OpenSSL (the executable)

Again, the modification to the default secure/usr.bin/openssl/Makefile is done exactly like the libcrypto modification.

The Makefile as imported from OpenBSD required very little modification to work.

One more thing...

This build was just a bit of hacking. Linking openssl failed, and a bit of digging showed that libssl was incorrectly linked as well, it linked This is due to the way I was building and linking. To solve I dropped into the /usr/obj tree and linked libssl and openssl separately using the commmands from the build logs of libssl and openssl.

cd /usr/obj/usr/src/secure/lib/libssl
cc  ... bs_cbs.So | tsort -q` -lcrypto -L../libcrypto
cd /usr/src/secure/lib/libssl

cd /usr/obj/usr/src/secure/usr.bin/openssl
cc ... x509.o   -lssl  -lcrypto -L../../lib/libcrypto -L../../lib/libssl
cd /usr/src/secure/usr.bin/openssl

Checks with readelf -d show that libssl and openssl now link correctly!

Install & verify

Now we can install libcrypto, libssl and openssl

cd /usr/src/secure/lib/libcrypto
make install
cd /usr/src/secure/lib/libssl
make install
cd /usr/src/secure/usr.bin/openssl
make install

And voilá we have a working LibreSSL in base!

which openssl

openssl version
LibreSSL 2.3.2

readelf -d /usr/bin/openssl
Dynamic section at offset 0x67028 contains 23 entries:
  Tag                Type    Name/Value
 0x0000000000000001 NEEDED Shared library: []
 0x0000000000000001 NEEDED Shared library: []
 0x0000000000000001 NEEDED Shared library: []


So far so good! Building is only half of the work, the proof of the pudding is in the eating.

Next up:

  1. Building world with LibreSSL
  2. Add assembly optimizations
  3. Polish code
  4. Add libtls and LibreSSL's TLS-capable nc