Posts

Another month down! Feels like I just wrote the March 2021 post… but I suppose that is what happens when your project moves super quickly :) Linux kernel patches [PATCH] ACPI / CPPC: Replace cppc_attr with kobj_attribute: I discovered this issue as part of my testing of Sami Tolvanen’s Control Flow Integrity series (more on that below). There are probably many more of these lurking because this pattern is hard to spot without runtime testing. As I have time amongst all of the other issues and such, I will be testing the x86 variant of CFI on several different servers, trying to flush out all of the different issues there. ...

Another month, another post about the work that I have done as a kernel/compiler developer! One of the highlights this month is that I got LLVM commit access so I can merge my own patches into LLVM, which I did twice so far. Linux kernel patches powerpc/fadump: Mark fadump_calculate_reserve_size as __init: LLVM 13 switched over to the New Pass Manager (NPM), which has impacted some inlining decisions, which in turn exposed some bugs in section annotations. The kernel places certain functions and variables into specific sections that are discarded and freed after init. If a non-init function calls an init function, that is technically a use-after-free so the kernel warns when this happens. In this particular case, identical_pvr_fixup() was not marked as __init and it was not getting inlined so the calls to identify_cpu() and of_get_flat_dt_prop() resulting in the modpost warnings. In practice, this is not an issue because identical_pvr_fixup() is only called from __init context but it is important to get these things right so that real warnings can easily be caught. ...

As some of you may or may not know by now, I am now employed by the Linux Foundation to help improve Linux security. The primary way that I am doing that is through the work I do for ClangBuiltLinux, of which I am an official maintainer. Linux kernel patches First and foremost, I am a Linux kernel developer, meaning that I love sending kernel patches. Getting familiar with git send-email and the standard Linux kernel workflow can be difficult but now that I am used to it, I find other things cumbersome. ...

Before Google+ shut down, I had a post on there giving a brief overview of git bisect, which a lot of people found useful. Unfortunately, I forgot to save it and move it somewhere else before the shutdown deadline. As a result, I am going to redo it here and spice it up a bit. One caveat before I start: there is great official documentation for git bisect, from which I have taken quite a bit of information. If I say something that contradicts what the documentation says, assume the documentation is right. ...

I have always loved reading good commit messages and I have tried myself to write good commit messages to inspire others to do the same. I see good commit messages as important for two reasons: it allows people who work on a project afterwards to understand the context behind a change (so that you don’t have a denvercoder9 situation) and it allows other people to get familiar with your project by fully understanding the why behind a change. I learned a lot about the Linux kernel purely through reading the commit messages in certain subsystems. ...

I have been a big fan of Windows Subsystem for Linux 2 as I need Windows for school but I am so used to the command line for remoting into my server and automating various tasks locally. For those of you who do not know, WSL 2 uses a Linux kernel under the hood (which I customize here) and all of the various distributions that you can run are basically containers on top of it. ...

Recently, I stumbled upon a talk that Alistair Delva, a Google engineer, gave at the 2018 Linux Plumbers Conference around Cuttlefish, an Android Virtual Device (AVD) that is used to validate the Android platform virtually (i.e. without a separate device). This is something that is really cool because it makes it easy to follow along with upstream Android development and see what changes they are making under the hood, all from adb shell. Cuttlefish boots in around 20 seconds on my machine and swapping out kernels is as simple as adding two command flags which I will go over later. If you are running Cuttlefish locally, you can even view it with TightVNC. ...

Recently, I built a computer for school that I installed Windows 10 Pro on (link to the current specs if you are curious). I was a little bummed about leaving Chrome OS because I was going to lose my local Linux development environment; however, Windows Subsystem for Linux is a thing and it has gotten even better with WSL 2, as it is actually running a Linux kernel so there is full Linux compatibility going forward. I also learned that it is possible to replace the Linux kernel that Microsoft ships with your own. This is a mini guide for what I uncovered because there is not a ton of information around for how to do this. ...