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Episode 254: Bare the OS

2018-07-11

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Headlines

Cross-DSO CFI in HardenedBSD

Control Flow Integrity, or CFI, raises the bar for attackers aiming to hijack control flow and execute arbitrary code. The llvm compiler toolchain, included and used by default in HardenedBSD 12-CURRENT/amd64, supports forward-edge CFI. Backward-edge CFI support is gained via a tangential feature called SafeStack. Cross-DSO CFI builds upon ASLR and PaX NOEXEC for effectiveness. HardenedBSD supports non-Cross-DSO CFI in base for 12-CURRENT/amd64 and has it enabled for a few individual ports. The term "non-Cross-DSO CFI" means that CFI is enabled for code within an application's codebase, but not for the shared libraries it depends on. Supporting non-Cross-DSO CFI is an important initial milestone for supporting Cross-DSO CFI, or CFI applied to both shared libraries and applications. This article discusses where HardenedBSD stands with regards to Cross-DSO CFI in base. We have made a lot of progress, yet we're not even half-way there. Brace yourself: This article is going to be full of references to "Cross-DSO CFI." Make a drinking game out of it. Or don't. It's your call. ;)

  • Using More llvm Toolchain Components

CFI requires compiling source files with Link-Time Optimization (LTO). I remembered hearing a few years back that llvm developers were able to compile the entirety of FreeBSD's source code with LTO. Compiling with LTO produces intermediate object files as LLVM IR bitcode instead of ELF objects. In March of 2017, we started compiling all applications with LTO and non-Cross-DSO CFI. This also enabled ld.lld as the default linker in base since CFI requires lld. Commit f38b51668efcd53b8146789010611a4632cafade made the switch to ld.lld as the default linker while enabling non-Cross-DSO CFI at the same time. Building libraries in base requires applications like ar, ranlib, nm, and objdump. In FreeBSD 12-CURRENT, ar and ranlib are known as "BSD ar" and "BSD ranlib." In fact, ar and ranlib are the same applications. One is hardlinked to another and the application changes behavior depending on arvgv[0] ending in "ranlib". The ar, nm, and objdump used in FreeBSD do not support LLVM IR bitcode object files. In preparation for Cross-DSO CFI support, commit fe4bb0104fc75c7216a6dafe2d7db0e3f5fe8257 in October 2017 saw HardenedBSD switching ar, ranlib, nm, and objdump to their respective llvm components. The llvm versions due support LLVM IR bitcode object files (surprise!) There has been some fallout in the ports tree and we've added LLVMARUNSAFE and friends to help transition those ports that dislike llvm-ar, llvm-ranlib, llvm-nm, and llvm-objdump. With ld.lld, llvm-ar, llvm-ranlib, llvm-nm, and llvm-objdump the default, HardenedBSD has effectively switched to a full llvm compiler toolchain in 12-CURRENT/amd64.

  • Building Libraries With LTO

The primary 12-CURRENT development branch in HardenedBSD (hardened/current/master) only builds applications with LTO as mentioned in the secion above. My first attempt at building all static and shared libraries failed due to issues within llvm itself. I reported these issues to FreeBSD. Ed Maste (emaste@), Dimitry Andric (dim@), and llvm's Rafael Espindola expertly helped address these issues. Various commits within the llvm project by Rafael fully and quickly resolved the issues brought up privately in emails. With llvm fixed, I could now build nearly every library in base with LTO. I noticed, however, that if I kept non-Cross-DSO CFI and SafeStack enabled, all applications would segfault. Even simplistic applications like /bin/ls. Disabling both non-Cross-DSO CFI and SafeStack, but keeping LTO produced a fully functioning world! I have spent the last few months figuring out why enabling either non-Cross-DSO CFI or SafeStack caused issues. This brings us to today.

  • The Sanitizers in FreeBSD

FreeBSD brought in all the files required for SafeStack and CFI. When compiling with SafeStack, llvm statically links a full sanitization framework into the application. FreeBSD includes a full copy of the sanitization framework in SafeStack, including the common C++ sanization namespaces. Thus, libclangrt.safestack included code meant to be shared among all the sanitizers, not just SafeStack. I had naively taken a brute-force approach to setting up the libclangrt.cfi static library. I copied the Makefile from libclangrt.safestack and used that as a template for libclangrt.cfi. This approach was incorrect due to breaking the One Definition Rule (ODR). Essentially, I ended up including a duplicate copy of the C++ classes and sanitizer runtime if both CFI and SafeStack were used. In my Cross-DSO CFI development VM, I now have SafeStack disabled across-the-board and am only compiling in CFI. As of 26 May 2018, an LTO-ified world (libs + apps) works in my limited testing. /bin/ls does not crash anymore! The second major milestone for Cross-DSO CFI has now been reached.

  • Known Issues And Limitations

There are a few known issues and regressions. Note that this list of known issues essentially also constitutes a "work-in-progress" and every known issue will be fixed prior to the official launch of Cross-DSO CFI. It seems llvm does not like statically compiling applications with LTO that have a mixture of C and C++ code. /sbin/devd is one of these applications. As such, when Cross-DSO CFI is enabled, devd is compiled as a Position-Independent Executable (PIE). Doing this breaks UFS systems where /usr is on a separate partition. We are currently looking into solving this issue to allow devd to be statically compiled again. NOSHARED is now unset in the tools build stage (aka, bootstrap-tools, cross-tools). This is related to the static compilation issue above. Unsetting NOSHARED for to tools build stage is only a band-aid until we can resolve static compliation with LTO. One goal of our Cross-DSO CFI integration work is to be able to support the cfi-icall scheme when dlopen(3) and dlsym(3)/dlfunc(3) is used. This means the runtime linker (RTLD), must be enhanced to know and care about the CFI runtime. This enhancement is not currently implemented, but is planned. When Cross-DSO CFI is enabled, SafeStack is disabled. This is because compiling with Cross-DSO CFI brings in a second copy of the sanitizer runtime, violating the One Definition Rule (ODR). Resolving this issue should be straightforward: Unify the sanitizer runtime into a single common library that both Cross-DSO CFI and SafeStack can link against. When the installed world has Cross-DSO CFI enabled, performing a buildworld with Cross-DSO CFI disabled fails. This is somewhat related to the static compilation issue described above.

  • Current Status

I've managed to get a Cross-DSO CFI world booting on bare metal (my development laptop) and in a VM. Some applications failed to work. Curiously, Firefox still worked (which also means xorg works). I'm now working through the known issues list, researching and learning.

  • Future Work

Fixing pretty much everything in the "Known Issues And Limitations" section. ;P I need to create a static library that includes only a single copy of the common sanitizer framework code. Applications compiled with CFI or SafeStack will then only have a single copy of the framework. Next I will need to integrate support in the RTLD for Cross-DSO CFI. Applications with the cfi-icall scheme enabled that call functions resolved through dlsym(3) currently crash due to the lack of RTLD support. I need to make a design decision as to whether to only support adding cfi-icall whitelist entries only with dlfunc(3) or to also whitelist cfi-icall entries with the more widely used dlsym(3). There's likely more items in the "TODO" bucket that I am not currently aware of. I'm treading in uncharted territory. I have no firm ETA for any bit of this work. We may gain Cross-DSO CFI support in 2018, but it's looking like it will be later in either 2019 or 2020.

  • Conclusion

I have been working on Cross-DSO CFI support in HardenedBSD for a little over a year now. A lot of progress is being made, yet there's still some major hurdles to overcome. This work has already helped improve llvm and I hope more commits upstream to both FreeBSD and llvm will happen. We're getting closer to being able to send out a preliminary Call For Testing (CFT). At the very least, I would like to solve the static linking issues prior to publishing the CFT. Expect it to be published before the end of 2018. I would like to thank Ed Maste, Dimitry Andric, and Rafael Espindola for their help, guidance, and support.


iXsystems FreeNAS 11.2-BETAs are starting to appear

Bareos Backup Server on FreeBSD

Ever heard about Bareos? Probably heard about Bacula. Read what is the difference here – Why Bareos forked from Bacula? Bareos (Backup Archiving Recovery Open Sourced) is a network based open source backup solution. It is 100% open source fork of the backup project from bacula.org site. The fork is in development since late 2010 and it has a lot of new features. The source is published on github and licensed under AGPLv3 license. Bareos supports ‘Always Incremental backup which is interesting especially for users with big data. The time and network capacity consuming full backups only have to be taken once. Bareos comes with WebUI for administration tasks and restore file browser. Bareos can backup data to disk and to tape drives as well as tape libraries. It supports compression and encryption both hardware-based (like on LTO tape drives) and software-based. You can also get professional services and support from Bareos as well as Bareos subscription service that provides you access to special quality assured installation packages.

I started my sysadmin job with backup system as one of the new responsibilities, so it will be like going back to the roots. As I look on the ‘backup’ market it is more and more popular – especially in cloud oriented environments – to implement various levels of protection like GOLD, SILVER and BRONZE for example. They of course have different retention times, number of backups kept, different RTO and RPO. Below is a example implementation of BRONZE level backups in Bareos. I used 3 groups of A, B and C with FULL backup starting on DAY 0 (A group), DAY 1 (B group) and DAY 2 (C group). This way you still have FULL backups quite often and with 3 groups you can balance the network load. I for the days that we will not be doing FULL backups we will be doing DIFFERENTIAL backups. People often confuse them with INCREMENTAL backups. The difference is that DIFFERENTIAL backups are always against FULL backup, so its always ‘one level of combining’. INCREMENTAL ones are done against last done backup TYPE, so its possible to have 100+ levels of combining against 99 earlier INCREMENTAL backups and the 1 FULL backup. That is why I prefer DIFFERENTIAL ones here, faster recovery. That is all backups is about generally, recovery, some people/companies tend to forget that. The implementation of BRONZE in these three groups is not perfect, but ‘does the job’. I also made ‘simulation’ how these group will overlap at the end/beginning of the month, here is the result. Not bad for my taste.

Today I will show you how to install and configure Bareos Server based on FreeBSD operating system. It will be the most simplified setup with all services on single machine:

  • bareos-dir
  • bareos-sd
  • bareos-webui
  • bareos-fd

I also assume that in order to provide storage space for the backup data itself You would mount resources from external NFS shares.

To get in touch with Bareos terminology and technology check their great Manual in HTML or PDF version depending which format You prefer for reading documentation. Also their FAQ provides a lot of needed answers.

Also this diagram may be useful for You to get some grip into the Bareos world.

  • System

As every system needs to have its name we will use latin word closest to backup here – replica – for our FreeBSD system hostname. The install would be generally the same as in the FreeBSD Desktop – Part 2 – Install article. Here is our installed FreeBSD system with login prompt.

Here are 3 most important configuration files after some time in vi(1) with them.

root@replica:~ # cat /etc/rc.conf

NETWORK

hostname=replica.backup.org ifconfig_em0="inet 10.0.10.30/24 up" defaultrouter="10.0.10.1"

DAEMONS

zfsenable=YES sshdenable=YES nfsclientenable=YES syslogdflags="-ss" sendmailenable=NONE

OTHER

cleartmpenable=YES dumpdev=NO

BAREOS

postgresql_enable=YES

postgresql_class=pgsql

bareosdirenable=YES

bareossdenable=YES

bareosfdenable=YES

phpfpmenable=YES

nginx_enable=YES

As You can see all ‘core’ services for Bareos are currently disabled on purpose. We will enable them later. ```

  • Parameters and modules to be set at boot.

``` root@replica:~ # cat /boot/loader.conf

BOOT OPTIONS

autobootdelay=2 kern.geom.label.diskident.enable=0 kern.geom.label.gptid.enable=0

MODULES

zfs_load=YES

IPC

kern.ipc.shmseg=1024 kern.ipc.shmmni=1024 kern.ipc.shmseg=1024 ``` + Parameters to be set at runtime.

``` root@replica:~ # cat /etc/sysctl.conf

SECURITY

security.bsd.seeotheruids=0 security.bsd.seeothergids=0 security.bsd.unprivilegedreadmsgbuf=0 security.bsd.unprivilegedprocdebug=0 security.bsd.stackguardpage=1 kern.randompid=9100

ZFS

vfs.zfs.minautoashift=12

DISABLE ANNOYING THINGS

kern.coredump=0 hw.syscons.bell=0 kern.vt.enable_bell=0

IPC

kern.ipc.shmall=524288 kern.ipc.maxsockbuf=5242880 kern.ipc.shmallowremoved=1 ```

After install we will disable the /zroot mounting.

  • Visit the article to see all the information about
    • Packages
    • PostgreSQL
    • Storage
    • BareOS
    • Pools
    • BareOS WebUI
    • Logs
    • Skel

Fixing bufferbloat on your home network with OpenBSD 6.2 or newer

My home network (which is also my work network) is a standard-issue Comcast cable hookup. In spite of a tolerable 120 megabits down, my experience of daily Internet use is regularly frustrating. Video streams and video chats drop in quality inexplicably. SSH sessions become laggy. Web pages fail to load quickly, and then seem to appear all at once. Even though I should have plenty of bandwidth, the feeling is often one of slowness, waiting, data struggling to get through the pipes. The reason for this is a phenomenon called "bufferbloat". I'm not going to explain it in detail, there are plenty of good resources to read about it, including the eponymous Bufferbloat.net. Bufferbloat is the result of complex interactions between the software and hardware systems routing traffic around on the Internet. It causes higher latency in networks, even ones with plenty of bandwidth. In a nutshell, software queues in our routers are not letting certain packets through fast enough to ensure that things feel interactive and responsive. Pings, TCP ACKs, SSH connections, are all being held up behind a long line of packets that may not need to be delivered with the same urgency. There's enough bandwidth to process the queue, the trick is to do it more quickly and more fairly. Fortunately, because bufferbloat is in part a function of how we configure our routers, it's within our ability to solve the problem. But first, we have to diagnose it, and establish a concrete baseline to improve from. The speed test at dslreports.com tests for bufferbloat in addition download and upload speeds, so we'll use that tool to see how we're doing. We define bufferbloat here as the increased latency of a standard ping while downloading or uploading a large file over ping times while otherwise quiescent. In our case, our idle latency is 12ms average, a download bloat of about 660ms, and an upload bloat of about 280ms, on average. Details vary widely by router operating system and administrative UIs. In our case, the router is running OpenBSD. (And if yours isn't, why not? Get a PC Engines board, throw obsd on it, and you have an inexpensive solution with world-class security, efficiency, and performance, that's simple to operate and well-documented.) The OpenBSD way of being a router is through its pf system, which is analogous to Linux's iptables, but much more capable and efficient. Since 6.2, pf has implemented something called "FQ-CoDel", which is an algorithm for scheduling packets fairly and is designed to prevent bufferbloat. It is exposed via the flows option on a queue rule. In principle, all we need to do is add two rules, one to fix uplink bufferbloat and one to fix downlink. Let's see how this goes. In our /etc/pf.conf, we first add a single line to handle the uplink. This will apply a FQ-CoDel queue to the network interface attached to our WAN link, or the cable modem in our case. The way to think about it is, FQ-CoDel is strategy applied to outbound packets only, as they exit the interface, so even though the WAN interface is duplex up and down, in order to handle the downlink part we'll apply it to the network interface connected to our LAN, which we'll do next. An important detail. In order for the queue algorithm to do its thing, it needs to know the bandwidth of the outbound link. According to Mike Belopuhov, the implementor of FQ-CoDel in OpenBSD, we need to specify 90-95% of the available bandwidth. Fortunately, we've just measured it. The line to add to pf.conf to fix bufferbloat on the uplink is (assuming em0 for the WAN interface): queue outq on em0 flows 1024 bandwidth 11M max 11M qlimit 1024 default A couple of notes. outq is a label we give, but it's an opaque string to pf. 11M means 11 megabits per second (92% of the uplink bandwidth). qlimit is also specified explicitly, because its default value of 50 is too low for FQ-CoDel. The default keyword is required. + Check out the full article for more details on pf configurations against bufferbloat. + Thanks go out the Frank Moore for sending us this any many more stories from the BSD world each week! It’s appreciated!


News Roundup

libcsi - Crypto Simplified Interface

Joel Sing (jsing@) has committed Crypto Simplified Interface (CSI) to -current:

``` CVSROOT: /cvs Module name: src Changes by: jsing@cvs.openbsd.org 2018/06/02 11:40:33

Added files: lib/libcsi : Makefile Symbols.list csi.c csi.h csidh.c csidhgroups.c csiinternal.h csiutil.c shlibversion

Log message: Initial version of Crypto Simplified Interface (CSI).

This is a code base that intends on providing a simplified interface for mid-level cryptographic operations. In due course various applications and libraries will be able to benefit from a clean and robust API, rather than using libcrypto or other similar APIs directly.

Discussed at length with deraadt@, djm@, markus@, beck@ and others. ```

This parallels the addition of libtls.


Digital Ocean http://do.co/bsdnow

MeetBSD Call for Papers

  • CFP closes on August 13, 2018 07:00 UTC (so the night of August 12th) > MeetBSD 2018 is a mixed unConference format event featuring both scheduled talks and community-driven events such as birds-of-a-feather meetings and speed geeking sessions. > MeetBSD can be traced back to its humble roots as a local workshop for BSD developers and users, hosted annually in Poland since 2004. Since then, MeetBSD has grown into its own conference with participants from around the world. > The first MeetBSD California was held at Google HQ in 2008. The 2010, 2012, 2014, and 2016 conferences were held at Hacker Dojo in Mountain View, Yahoo! HQ, Western Digital, and UC Berkeley. To this day, MeetBSD California continues to be a biennial tradition in the Silicon Valley. MeetBSD 2018 will be hosted at Intel’s campus in Santa Clara. > Please provide a 100 word or longer description of your proposed talk and an outline of points you will cover.

And now for something entirely different… Twitter gems

  • https://twitter.com/RealGeneKim/status/1014949827031982080?s=19
  • https://twitter.com/postgresql/status/1016019087460356097?s=19
  • https://twitter.com/gumnos/status/1014982713026150400
  • https://twitter.com/vmisev/status/1014578693707100166
  • https://twitter.com/FranckPachot/status/1012606253338591232
  • https://twitter.com/lattera/status/1016398364722819072
  • https://twitter.com/changelog/status/1015234147307188225
  • https://twitter.com/canadianbryan/status/1013823795499618305

Also this week in FreeBSD:


Beastie Bits


Tarsnap

Feedback/Questions


  • Send questions, comments, show ideas/topics, or stories you want mentioned on the show to feedback@bsdnow.tv

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