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What distro options are there for POWER8 in 2022?

If you have POWER8 systems that you want to keep alive, what are your options in 2022? You can keep using the legacy distribution you're still using as long as it's still supported, but if you want some modernisation, that might not be the best option for you. Here's the current landscape of POWER8 support in major distributions, and hopefully it helps you out!

Please note that I am entirely focused on what runs and keeps getting new packages, not what companies will officially support. IBM provides documentation for that. I'm also mostly focused on OpenPOWER and not what's supported under IBM PowerVM.


Things aren't too great on the RHEL-compatible side. RHEL 9 is compiled with P9 instructions, removing support for P8. This includes compatible distributions, like CentOS Stream and Rocky Linux.

You can continue to use RHEL 8 for a long time. Unfortunately, Rocky Linux only has a Power release for EL9 and not EL8, and CentOS Stream 8 hits EOL May 31st, 2024 - a bit too soon for my liking. If you're a RHEL customer though, you're set.


Fedora seems like a great option - the latest versions still support P8 and there's no immediate signs of that changing. The issue is that Fedora could change this with relatively little warning (and their big brother RHEL already has), Fedora doesn't provide LTS versions that will stay supported if this happens, and any options you could migrate to would be very different from what you're using.

For that reason, I don't recommend using Fedora on POWER8 if you intend to keep it around for a while. If you want something modern for a short-term project, go right ahead! Otherwise, I'd avoid it. If you're still keeping POWER8 systems alive, you probably want something more set-and-forget than Fedora anyway.


Ubuntu is a mixed bag. The good news is that Ubuntu 20.04 LTS is supported until mid-2025, and if you give Canonical money, that support can extend through 2030. Ubuntu 20.04 LTS is my personal pick for the best distro to install on POWER8 systems that you want to have somewhat modern software but without the risks of future issues.

The bad news is that POWER8 support went away in Ubuntu 22.04, which is extremely unfortunate. Missing an LTS cycle is one thing, but not having a pathway from 21.10 is another. If you were on 20.10/21.04/21.10, you are completely boned, because they're all out of support and 22.04 and later don't support POWER8. You're going to have to reinstall 20.04.

If I sound salty, it's because I had to do this for a few machines. Hopefully you're not in that situation. 20.04 is going to be around for a good while longer, with a lot of modern creature comforts you'd miss on an EL8-compatible distro, so it's my pick for now.


I'm pretty ignorant when it comes to chameleon-flavoured distros, so take this with a grain of salt as most of it is from some quick searching. OpenSUSE Leap follows SLES, but without extended support lifetimes for older major versions. From what I can tell, the latest release (15.4) still includes POWER8 support (and adds Power10 support!), but similar to Fedora, that looks rather prone to a new version dropping P8 support to me.

If the 15.x series stayed alive after 16 came out, you might be good, but it doesn't seem like there's a history of that happening.


Debian 11 "bullseye" came out in 2021, supports POWER8, and is likely to be supported until around 2026. I can't really chime in on more than that because I am a certified Debian hater (even newer releases feel outdated to me), but that looks like a pretty good deal.

Other options

Those are just some major distros, there's plenty of others, including some Power-specific ones from the community.


POWER8's getting old, but is still plenty capable. Make sure your distro still remembers to send your POWER8 a birthday card each year and you'll have plenty more good times to come.

Power kernel hardening features in Linux 6.1

Linux 6.1-rc1 was tagged on October 16th, 2022 and includes a bunch of nice things from my team that I want to highlight. Our goal is to make the Linux kernel running on IBM's Power CPUs more secure, and landed a few goodies upstream in 6.1 to that end.

Specifically, Linux 6.1 on Power will include a complete system call infrastructure rework with security and performance benefits, support for KFENCE (a low-overhead memory safety error detector), and execute-only memory (XOM) support on the Radix MMU.

The syscall work from Rohan McLure and Andrew Donnellan replaces arch/powerpc's legacy infrastructure with the syscall wrapper shared between architectures. This was a significant overhaul of a lot of legacy code impacting all of powerpc's many platforms, including multiple different ABIs and 32/64bit compatibility infrastructure. Rohan's series started at v1 with 6 patches and ended at v6 with 25 patches, and he's done an incredible job at adopting community feedback and handling new problems.

Big thanks to Christophe Leroy, Arnd Bergmann, Nick Piggin, Michael Ellerman and others for their reviews, and of course Andrew for providing a lot of review and feedback (and prototyping the syscall wrapper in the first place). Our syscalls have entered the modern era, we can zeroise registers to improve security (but don't yet due to some ongoing discussion around compatibility and making it optional, look out for Linux 6.2), and gain a nice little performance boost by avoiding the allocation of a kernel stack frame. For more detail, see Rohan's cover letter.

Next, we have Nicholas Miehlbradt's implementation of Kernel Electric Fence (KFENCE) (and DEBUG_PAGEALLOC) for 64-bit Power, including the Hash and Radix MMUs. Christophe Leroy has already implemented KFENCE for 32-bit powerpc upstream and a series adding support for 64-bit was posted by Jordan Niethe last year, but couldn't proceed due to locking issues. Those issues have since been resolved, and after fixing a previously unknown and very obscure MM issue, Nick's KFENCE patches have been merged.

KFENCE is a low-overhead alternative to memory detectors like KASAN (which we implemented for Radix earlier this year, thanks to Daniel Axtens and Paul Mackerras), which you probably wouldn't want to run in production. If you're chasing a memory corruption bug that doesn't like to present itself, KFENCE can help you do that for out-of-bounds accesses, use-after-frees, double frees etc without significantly impacting performance.

Finally, I wired up execute-only memory (XOM) for the Radix MMU. XOM is a niche feature that lets users map pages with PROT_EXEC only, creating a page that can't be read or written to, but still executed. This is primarily useful for defending against code reuse attacks like ROP, but has other uses such as JIT/sandbox environments. Power8 and later CPUs running the Hash MMU already had this capability through protection keys (pkeys), my implementation for Radix uses the native execute permission bit of the Radix MMU instead.

This basically took me an afternoon to wire up after I had the idea and I roped in Nicholas Miehlbradt to contribute a selftest, which ended up being a more significant engineering effort than the feature implementation itself. We now have a comprehensive test for XOM that runs on both Hash and Radix for all possible combinations of R/W/X upstream.

Anyway, that's all I have - this is my first time writing a post like this, so let me know what you think! A lot of our work doesn't result in upstream patches so we're not always going to have kernel releases as eventful as this, but we can post summaries every once in a while if there's interest. Thanks for reading!

Fuzzing grub, part 2: going faster

Recently a set of 8 vulnerabilities were disclosed for the grub bootloader. I found 2 of them (CVE-2021-20225 and CVE-2021-20233), and contributed a number of other fixes for crashing bugs which we don't believe are exploitable. I found them by applying fuzz testing to grub. Here's how.

This is a multi-part series: I think it will end up being 4 posts. I'm hoping to cover:

We've been looking at fuzzing grub-emu, which is basically most parts of grub built into a standard userspace program. This includes all the script parsing logic, fonts, graphics, partition tables, filesystems and so on - just not platform specific driver code or the ability to actually load and boot a kernel.

Previously, we talked about some issues building grub with AFL++'s instrumentation:

./configure --with-platform=emu --disable-grub-emu-sdl CC=$AFL_PATH/afl-cc
checking whether target compiler is working... no
configure: error: cannot compile for the target

It also doesn't work with afl-gcc.

We tried to trick configure:

./configure --with-platform=emu --disable-grub-emu-sdl CC=clang CXX=clang++
make CC="$AFL_PATH/afl-cc" 

Sadly, things still break:

/usr/bin/ld: disk.module:(.bss+0x20): multiple definition of `__afl_global_area_ptr'; kernel.exec:(.bss+0xe078): first defined here
/usr/bin/ld: regexp.module:(.bss+0x70): multiple definition of `__afl_global_area_ptr'; kernel.exec:(.bss+0xe078): first defined here
/usr/bin/ld: blocklist.module:(.bss+0x28): multiple definition of `__afl_global_area_ptr'; kernel.exec:(.bss+0xe078): first defined here

The problem is the module linkage that I talked about in part 1. There is a link stage of sorts for the kernel (kernel.exec) and each module (e.g. disk.module), so some AFL support code gets linked into each of those. Then there's another link stage for grub-emu itself, which also tries to bring in the same support code. The linker doesn't like the symbols being in multiple places, which is fair enough.

There are (at least) 3 ways you could solve this. I'm going to call them the hard way, and the ugly way and the easy way.

The hard way: messing with makefiles

We've been looking at fuzzing grub-emu. Building grub-emu links kernel.exec and almost every .module file that grub produces into the final binary. Maybe we could avoid our duplicate symbol problems entirely by changing how we build things?

I didn't do this in my early work because, to be honest, I don't like working with build systems and I'm not especially good at it. grub's build system is based on autotools but is even more quirky than usual: rather than just having a, we have Makefile.core.def which is used along with other things to generate It's a pretty cool system for making modules, but it's not my idea of fun to work with.

But, for the sake of completeness, I tried again.

It gets unpleasant quickly. The generated grub-core/ adds each module to platform_PROGRAMS, and then each is built with LDFLAGS_MODULE = $(LDFLAGS_PLATFORM) -nostdlib $(TARGET_LDFLAGS_OLDMAGIC) -Wl,-r,-d.

Basically, in the makefile this ends up being (e.g.):

tar.module$(EXEEXT): $(tar_module_OBJECTS) $(tar_module_DEPENDENCIES) $(EXTRA_tar_module_DEPENDENCIES) 
    @rm -f tar.module$(EXEEXT)
    $(AM_V_CCLD)$(tar_module_LINK) $(tar_module_OBJECTS) $(tar_module_LDADD) $(LIBS)

Ideally I don't want them to be linked at all; there's no benefit if they're just going to be linked again.

You can't just collect the sources and build them into grub-emu - they all have to built with different CFLAGS! So instead I spent some hours messing around with the build system. Given some changes to the python script that converts the Makefile.*.def files into files, plus some other bits and pieces, we can build grub-emu by linking the object files rather than the more-processed modules.

The build dies immediately after linking grub-emu in other components, and it requires a bit of manual intervention to get the right things built in the right order, but with all of those caveats, it's enough. It works, and you can turn on things like ASAN, but getting there was hard, unrewarding and unpleasant. Let's consider alternative ways to solve this problem.

The ugly way: patching AFL

What I did when finding the bugs was to observe that we only wanted AFL to link in its extra instrumentation at certain points of the build process. So I patched AFL to add an environment variable AFL_DEFER_LIB - which prevented AFL adding its own instrumentation library when being called as a linker. I combined this with the older CFG instrumentation, as the PCGUARD instrumentation brought in a bunch of symbols from LLVM which I didn't want to also figure out how to guard.

I then wrapped this in a horrifying script that basically built bits and pieces of grub with the environment variable on or off, in order to at least get the userspace tools and grub-emu built. Basically it set AFL_DEFER_LIB when building all the modules and turned it off when building the userspace tools and grub-emu.

This worked and it's what I used to find most of my bugs. But I'd probably not recommend it, and I'm not sharing the source: it's extremely fragile and brittle, the hard way is more generally applicable, and the easy way is nicer.

The easy way: adjusting linker flags

After posting part 1 of this series, I had a fascinating twitter DM conversation with @hackerschoice, who pointed me to some new work that had been done in AFL++ between when I started and when I published part 1.

AFL++ now has the ability to dynamically detect some duplicate symbols, allowing it to support plugins and modules better. This isn't directly applicable because we link all the modules in at build time, but in the conversation I was pointed to a linker flag which instructs the linker to ignore the symbol duplication rather than error out. This provides a significantly simpler way to instrument grub-emu, avoiding all the issues I'd previously been fighting so hard to address.

So, with a modern AFL++, and the patch from part 1, you can sort out this entire process like this:

./configure --with-platform=emu CC=clang CXX=clang++ --disable-grub-emu-sdl
make CC=/path/to/afl-clang-fast LDFLAGS="-Wl,--allow-multiple-definition"

Eventually it will error out, but ./grub-core/grub-emu should be successfully built first.

(Why not just build grub-emu directly? It gets built by grub-core/Makefile, but depends on a bunch of things made by the top-level makefile and doesn't express its dependencies well. So you can try to build all the things that you need separately and then cd grub-core; make ...flags... grub-emu if you want - but it's way more complicated to do it that way!)

Going extra fast: __AFL_INIT

Now that we can compile with instrumentation, we can use __AFL_INIT. I'll leave the precise details of how this works to the AFL docs, but in short it allows us to do a bunch of early setup only once, and just fork the process after the setup is done.

There's a patch that inserts a call to __AFL_INIT in the grub-emu start path in my GitHub repo.

All up, this can lead to a 2x-3x speedup over the figures I saw in part 1. In part 1 we saw around 244 executions per second at this point - now we're over 500:

afl-fuzz fuzzing grub, showing fuzzing happening

Finding more bugs with sanitisers

A 'sanitizer' refers to a set of checks inserted by a compiler at build time to detect various runtime issues that might not cause a crash or otherwise be detected. A particularly common and useful sanitizer is ASAN, the AddressSanitizer, which detects out-of-bounds memory accesses, use-after-frees and other assorted memory bugs. Other sanitisers can check for undefined behaviour, uninitialised memory reads or even breaches of control flow integrity.

ASAN is particularly popular for fuzzing. In theory, compiling with AFL++ and LLVM makes it really easy to compile with ASAN. Setting AFL_USE_ASAN=1 should be sufficient.

However, in practice, it's quite fragile for grub. I believe I had it all working, and then I upgraded my distro, LLVM and AFL++ versions, and everything stopped working. (It's possible that I hadn't sufficiently cleaned my source tree and I was still building based on the hard way? Who knows.)

I spent quite a while fighting "truncated relocations". ASAN instrumentation was bloating the binaries, and the size of all the *.module files was over 512MB, which I suspect was causing the issues. (Without ASAN, it only comes to 35MB.)

I tried afl-clang-lto: I installed lld, rebuilt AFL++, and managed to segfault the linker while building grub. So I wrote that off. Changing the instrumentation type to classic didn't help either.

Some googling suggested GCC's -mmodel, which in Clang seems to be -mcmodel, but CFLAGS="-mcmodel=large" didn't get me any further either: it's already added in a few different links.

My default llvm is llvm-12, so I tried building with llvm-9 and llvm-11 in case that helped. Both built a binary, but it would fail to start:

==375638==AddressSanitizer CHECK failed: /build/llvm-toolchain-9-8fovFY/llvm-toolchain-9-9.0.1/compiler-rt/lib/sanitizer_common/ "((SoftRssLimitExceededCallback)) == ((nullptr))" (0x423660, 0x0)

The same happens if I build with llvm-12 and afl-clang, the old-style instrumentation.

I spun up a Ubuntu 20.04 VM and build there with LLVM 10 and the latest stable AFL++. That didn't work either.

I had much better luck using GCC's and GCC's ASAN implementation, either with the old-school afl-gcc or the newer GCC plugin-based afl-gcc-fast. (I have some hypotheses around shared library vs static library ASAN, but having spent way more work time on this than was reasonable, I was disinclined to debug it further.) Here's what worked for me:

./configure --with-platform=emu --disable-grub-emu-sdl
# the ASAN option is required because one of the tools leaks memory and
# that breaks the generation of documentation.
# -Wno-nested-extern makes __AFL_INIT work on gcc
ASAN_OPTIONS=detect_leaks=0 AFL_USE_ASAN=1 make CC=/path/to/afl-gcc-fast LDFLAGS="-Wl,--allow-multiple-definition" CFLAGS="-Wno-nested-extern"

GCC doesn't support as many sanitisers as LLVM, but happily it does support ASAN. AFL++'s GCC plugin mode should get us most of the speed we would get from LLVM, and indeed the speed - even with ASAN - is quite acceptable.

If you persist, you should be able to find some more bugs: for example there's a very boring global array out-of-bounds read when parsing config files.

That's all for part 2. In part 3 we'll look at fuzzing filesystems and more. Hopefully there will be a quicker turnaround between part 2 and part 3 than there was between part 1 and part 2!

Fuzzing grub: part 1

Recently a set of 8 vulnerabilities were disclosed for the grub bootloader. I found 2 of them (CVE-2021-20225 and CVE-2021-20233), and contributed a number of other fixes for crashing bugs which we don't believe are exploitable. I found them by applying fuzz testing to grub. Here's how.

This is a multi-part series: I think it will end up being 4 posts. I'm hoping to cover:

  • Part 1 (this post): getting started with fuzzing grub
  • Part 2: going faster by doing lots more work
  • Part 3: fuzzing filesystems and more
  • Part 4: potential next steps and avenues for further work

Fuzz testing

Let's begin with part one: getting started with fuzzing grub.

One of my all-time favourite techniques for testing programs, especially programs that handle untrusted input, and especially-especially programs written in C that parse untrusted input, is fuzz testing. Fuzz testing (or fuzzing) is the process of repeatedly throwing randomised data at your program under test and seeing what it does.

(For the secure boot threat model, untrusted input is anything not validated by a cryptographic signature - so config files are untrusted for our purposes, but grub modules can only be loaded if they are signed, so they are trusted.)

Fuzzing has a long history and has recently received a new lease on life with coverage-guided fuzzing tools like AFL and more recently AFL++.

Building grub for AFL++

AFL++ is extremely easy to use ... if your program:

  1. is built as a single binary with a regular tool-chain
  2. runs as a regular user-space program on Linux
  3. reads a small input files from disk and then exits
  4. doesn't do anything fancy with threads or signals

Beyond that, it gets a bit more complex.

On the face of it, grub fails 3 of these 4 criteria:

  • grub is a highly modular program: it loads almost all of its functionality as modules which are linked as separate ELF relocatable files. (Not runnable programs, but not shared libraries either.)

  • grub usually runs as a bootloader, not as a regular app.

  • grub reads all sorts of things, ranging in size from small files to full disks. After loading most things, it returns to a command prompt rather than exiting.

Fortunately, these problems are not insurmountable.

We'll start with the 'running as a bootloader' problem. Here, grub helps us out a bit, because it provides an 'emulator' target, which runs most of grub functionality as a userspace program. It doesn't support actually booting anything (unsurprisingly) but it does support most other modules, including things like the config file parser.

We can configure grub to build the emulator. We disable the graphical frontend for now.

./configure --with-platform=emu --disable-grub-emu-sdl

At this point in building a fuzzing target, we'd normally try to configure with afl-cc to get the instrumentation that makes AFL(++) so powerful. However, the grub configure script is not a fan:

./configure --with-platform=emu --disable-grub-emu-sdl CC=$AFL_PATH/afl-cc
checking whether target compiler is working... no
configure: error: cannot compile for the target

It also doesn't work with afl-gcc.

Hmm, ok, so what if we just... lie a bit?

./configure --with-platform=emu --disable-grub-emu-sdl
make CC="$AFL_PATH/afl-gcc" 

(Normally I'd use CC=clang and afl-cc, but clang support is slightly broken upstream at the moment.)

After a small fix for gcc-10 compatibility, we get the userspace tools (potentially handy!) but a bunch of link errors for grub-emu:

/usr/bin/ld: disk.module:(.bss+0x20): multiple definition of `__afl_global_area_ptr'; kernel.exec:(.bss+0xe078): first defined here
/usr/bin/ld: regexp.module:(.bss+0x70): multiple definition of `__afl_global_area_ptr'; kernel.exec:(.bss+0xe078): first defined here
/usr/bin/ld: blocklist.module:(.bss+0x28): multiple definition of `__afl_global_area_ptr'; kernel.exec:(.bss+0xe078): first defined here

The problem is the module linkage that I talked about earlier: because there is a link stage of sorts for each module, some AFL support code gets linked in to both the grub kernel (kernel.exec) and each module (here disk.module, regexp.module, ...). The linker doesn't like it being in both, which is fair enough.

To get started, let's instead take advantage of the smarts of AFL++ using Qemu mode instead. This builds a specially instrumented qemu user-mode emulator that's capable of doing coverage-guided fuzzing on uninstrumented binaries at the cost of a significant performance penalty.

make clean

Now we have a grub-emu binary. If you run it directly, you'll pick up your system boot configuration, but the -d option can point it to a directory of your choosing. Let's set up one for fuzzing:

mkdir stage
echo "echo Hello sthbrx readers" > stage/grub.cfg
cd stage
../grub-core/grub-emu -d .

You probably won't see the message because the screen gets blanked at the end of running the config file, but if you pipe it through less or something you'll see it.

Running the fuzzer

So, that seems to work - let's create a test input and try fuzzing:

cd ..
mkdir in
echo "echo hi" > in/echo-hi

cd stage
# -Q qemu mode
# -M main fuzzer
# -d don't do deterministic steps (too slow for a text format)
# -f create file grub.cfg
$AFL_PATH/afl-fuzz -Q -i ../in -o ../out -M main -d -- ../grub-core/grub-emu -d .


[-] The program took more than 1000 ms to process one of the initial test cases.
    This is bad news; raising the limit with the -t option is possible, but
    will probably make the fuzzing process extremely slow.

    If this test case is just a fluke, the other option is to just avoid it
    altogether, and find one that is less of a CPU hog.

[-] PROGRAM ABORT : Test case 'id:000000,time:0,orig:echo-hi' results in a timeout
         Location : perform_dry_run(), src/afl-fuzz-init.c:866

What we're seeing here (and indeed what you can observe if you run grub-emu directly) is that grub-emu isn't exiting when it's done. It's waiting for more input, and will keep waiting for input until it's killed by afl-fuzz.

We need to patch grub to sort that out. It's on my GitHub.

Apply that, rebuild with FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION, and voila:

cd ..
cd stage
$AFL_PATH/afl-fuzz -Q -i ../in -o ../out -M main -d -f grub.cfg -- ../grub-core/grub-emu -d .

And fuzzing is happening!

afl-fuzz fuzzing grub, showing fuzzing happening

This is enough to find some of the (now-fixed) bugs in the grub config file parsing!

Fuzzing beyond the config file

You can also extend this to fuzzing other things that don't require the graphical UI, such as grub's transparent decompression support:

cd ..
rm -rf in out stage
mkdir in stage
echo hi > in/hi
gzip in/hi
cd stage
echo "cat thefile" > grub.cfg
$AFL_PATH/afl-fuzz -Q -i ../in -o ../out -M main -f thefile -- ../grub-core/grub-emu -d .

You should be able to find a hang pretty quickly with this, an as-yet-unfixed bug where grub will print output forever from a corrupt file: (your mileage may vary, as will the paths.)

cp ../out/main/hangs/id:000000,src:000000,time:43383,op:havoc,rep:16 thefile
../grub-core/grub-emu -d . | less # observe this going on forever

zcat, on the other hand, reports it as simply corrupt:

$ zcat thefile

gzip: thefile: invalid compressed data--format violated

(Feel free to fix that and send a patch to the list!)

That wraps up part 1. Eventually I'll be back with part 2, where I explain the hoops to jump through to go faster with the afl-cc instrumentation. 2020 recap

It's that time of year again. Most of OzLabs headed up to the Gold Coast for 2020. is one of the longest-running community-led Linux and Free Software events in the world, and attracts a crowd from Australia, New Zealand and much further afield. OzLabbers have been involved in LCA since the very beginning and this year was no exception with myself running the Kernel Miniconf and several others speaking.

The list below contains some of our highlights that we think you should check out. This is just a few of the talks that we managed to make it to - there's plenty more worthwhile stuff on the YouTube channel.

We'll see you all at LCA2021 right here in Canberra...


A couple of the keynotes really stood out:

Sean is a forensic structural engineer who shows us a variety of examples, from structural collapses and firefighting disasters, where trained professionals were blinded by their expertise and couldn't bring themselves to do things that were obvious.

There's nothing quite like cryptography proofs presented to a keynote audience at 9:30 in the morning. Vanessa goes over the issues with electronic voting systems in Australia, and especially internet voting as used in NSW, including flaws in their implementation of cryptographic algorithms. There continues to be no good way to do internet voting, but with developments in methodologies like risk-limiting audits there may be reasonably safe ways to do in-person electronic voting.


There was an OpenISA miniconf, co-organised by none other than Hugh Blemings of the OpenPOWER Foundation.

Anton (on Mikey's behalf) introduces the Power OpenISA and the Microwatt FPGA core which has been released to go with it.

Anton live demos Microwatt in simulation, and also tries to synthesise it for his FPGA but runs out of time...

Paul presents an in-depth overview of the design of the Microwatt core.


There were quite a few kernel talks, both in the Kernel Miniconf and throughout the main conference. These are just some of them:

There's been many cases where we've introduced a syscall only to find out later on that we need to add some new parameters - how do we make our syscalls extensible so we can add new parameters later on without needing to define a whole new syscall, while maintaining both forward and backward compatibility? It turns out it's pretty simple but needs a few more kernel helpers.

There are a bunch of tools out there which you can use to make your kernel hacking experience much more pleasant. You should use them.

Among other security issues with container runtimes, using procfs to setup security controls during the startup of a container is fraught with hilarious problems, because procfs and the Linux filesystem API aren't really designed to do this safely, and also have a bunch of amusing bugs.

Control Flow Integrity is a technique for restricting exploit techniques that hijack a program's control flow (e.g. by overwriting a return address on the stack (ROP), or overwriting a function pointer that's used in an indirect jump). Kees goes through the current state of CFI supporting features in hardware and what is currently available to enable CFI in the kernel.

Linux has supported huge pages for many years, which has significantly improved CPU performance. However, the huge page mechanism was driven by hardware advancements and is somewhat inflexible, and it's just as important to consider software overhead. Matthew has been working on supporting more flexible "large pages" in the page cache to do just that.

Spoiler: the magical fantasy land is a trap.


Lots of community and ethics discussion this year - one talk which stood out to me:

Bradley and Karen argue that while open source has "won", software freedom has regressed in recent years, and present their vision for what modern, pragmatic Free Software activism should look like.


Among the variety of other technical talks at LCA...

Quantum compilers are not really like regular classical compilers (indeed, they're really closer to FPGA synthesis tools). Matthew talks through how quantum compilers map a program on to IBM's quantum hardware and the types of optimisations they apply.

Clevis and Tang provide an implementation of "network bound encryption", allowing you to magically decrypt your secrets when you are on a secure network with access to the appropriate Tang servers. This talk outlines use cases and provides a demonstration.

Christoph discusses how to deal with the hardware and software limitations that make it difficult to capture traffic at wire speed on fast fibre networks.