Wandering Thoughts

2019-01-08

Link: The IOCCC 2018 "Best of show" program

Christopher Mills' IOCCC 2018 entry (via) is a stunning tour de force that, well, let me quote the author's introduction:

The program delivered here is both a full machine emulation of the original PDP-7 that Ken Thompson used to write the first version of UNIX and a full machine emulation of the PDP-11/40 used by subsequent UNIXes. The Makefile can build versions that can run each of the following:

  1. UNIX v0 for the PDP-7 (circa 1969)
  2. Research UNIX Version 6 (circa 1975)
  3. BSD 2.9 (circa 1983)

This is one of those IOCCC entries where you absolutely do want to read the full author's description of their entry, because it is fascinating all by itself. For instance, until I read this I didn't know that Unix v0 had been reconstructed from original printouts of the assembly, and it's even on Github. That is just one small part of a fascinating journey.

(The IOCCC is the International Obfuscated C Code Contest, and here are the entire 2018 results. Mills' work may be even more impressive once you know that IOCCC entries must be 4096 bytes or less of C code.)

IOCCC2018BestOfShow written at 21:03:00; Add Comment

2018-12-14

Link: Everything you should know about certificates and PKI but are too afraid to ask

Mike Malone's Everything you should know about certificates and PKI but are too afraid to ask (via, also, also) starts off slow (and with one simplification that irritated me) but very soon gets rolling into things like X.509 and PKCS, and then gets into a thorough and solid discussion of PKI (Public key infrastructure) and the considerations of running your own internal one for (mutual) TLS authentication. I was very pleased to see this recommendation:

In any case, if you run your own internal PKI you should maintain a separate trust store for internal stuff. That is, instead of adding your root certificate(s) to the existing system trust store, configure internal TLS requests to use only your roots. [...]

Separating public 'web PKI' from your own internal PKI is an important measure to keep compromises in your internal PKI from leaking into your use of web PKI (both through browsers and through programs). It also keeps compromises in web PKI from hurting your internal PKI, which I believe is Malone's main focus.

The article isn't perfect, but it's a great introduction and overview with solid practical recommendations that goes into significant depth on some important issues.

(I'm fairly certain that I learned some new things from it, even though I'm pretty well exposed to all of this stuff already.)

PKIEverythingToKnow written at 09:26:50; Add Comment

2018-12-08

Link: HTTPS in the real world

Robert Heaton's article HTTPS in the real world (via) is about the difference between HTTPS in theory, in the cryptographic world of Alice and Bob, and HTTPS in practice, in the messy real world where CAs cannot be fully trusted and people lose their keys and so on. To pick one little bit to quote:

[...] But the real world has still managed to piece together a very serviceable public-key cryptography system by patching over the holes and omissions and naivety of the introductory world with a tartan of secondary systems known collectively as “Public Key Infrastructure” (PKI).

The whole article is a clear, short, amusing, and interesting summary of the whole practical mess of HTTPS and TLS. Even though I'm pretty up on all of the issues it talks about, I still found it well worth reading.

HTTPSRealWorld written at 00:10:01; Add Comment

2018-10-28

Link: HiDPI on dual 4K monitors with Linux

Vincent Bernat's article HiDPI on dual 4K monitors with Linux (via) is about what you'd expect it to be about and is, as they say, relevant to my interests. Especially relevant to me is the section on HiDPI support on Linux with X11, which runs down a collection of issues and contains a very useful chart about what is supported in what application and toolkit, which added some information that I hadn't known.

Note that Bernat's experience with xterm and rxvt don't match mine, perhaps because we're setting the X-level DPI information in somewhat different ways. My experience, as covered here, is that plain X applications using XFT fonts scale them appropriately once you get the DPI set everywhere (ie, if you tell xterm to use Monospace-12, you will get an actual 12 point size on your HiDPI monitor, not 12 points at 96 DPI and thus tiny fonts). If you use bitmap fonts, though, you're in trouble and unfortunately xterm still uses those by default for some things, like its popup menus.

(It's the nature of these articles to become out of date over time as HiDPI support improves and changes, but it's still a useful snapshot and some of these applications will probably never change.)

HiDPIOnDualMonitors written at 16:17:29; Add Comment

2018-10-18

Link: Vectorized Emulation [of CPUs and virtual machines]

Vectorized Emulation: Hardware accelerated taint tracking at 2 trillion instructions per second (via) is about, well, let me quote from the introduction rather than try to further summarize it:

In this blog I’m going to introduce you to a concept I’ve been working on for almost 2 years now. Vectorized emulation. The goal is to take standard applications and JIT them to their AVX-512 equivalent such that we can fuzz 16 VMs at a time per thread. The net result of this work allows for high performance fuzzing (approx 40 billion to 120 billion instructions per second [the 2 trillion clickbait number is theoretical maximum]) depending on the target, while gathering differential coverage on code, register, and memory state.

Naturally you need to do all sorts of interesting tricks to make this work. The entry is an overview, and the author is going to write more entries later on the details of various aspects of it, which I'm certainly looking forward to even if I'm not necessarily going to fully follow the details.

I found this interesting both by itself and for giving me some more insight into modern SIMD instructions and what goes into using them. SIMD and GPU computing feel like something that I should understand some day.

(I find SIMD kind of mind bending and I've never really dug into how modern x86 machines do this sort of stuff and what you use it for.)

VectorizedEmulation written at 20:06:28; Add Comment

2018-09-02

Link: "The History of a Security Hole" (in various *BSD kernels)

To yank my words from Twitter, Michal Necasek's The History of a Security Hole is a fascinating exploration of both the arcana of the x86 and what C can innocently do to you. Watching the code train barrel down the tracks towards its doom was decidedly compelling. There are also some useful lessons for long term software development that can be extracted here, since many of the mistakes made were entirely natural ones.

I often find this sort of stuff fascinating, so I really liked reading this entry and found I couldn't look away once things got going and mistakes piled up on top of misunderstandings. By the way, don't read this as a slam on the *BSDs; this sort of cascading misunderstanding can happen in any software, and undoubtedly has happened in non-BSD kernels as well in spots. It's simply easy to miss things in large, complex software (see eg).

(My tweet. I'm not sure where I got this from, but see HN, which mentions an interesting additional detail.)

SecurityHoleHistory written at 22:22:15; Add Comment

2018-08-31

Link: A deep dive into the Go memory allocator

Allocator Wrestling is a summary of Eben Freeman's talk from GopherCon 2018 on the Go memory allocator (via, and see also) and its garbage collection system. The slides are here (via) and have more details and elaborations on various things than the livebloged summary, although you probably want to read both (good talks are rarely entirely captured by their slides).

I love seeing under the hood of a complex system this way, and it's probably helped me move towards understanding some things about how much memory Go programs use (or appear to use).

GoAllocatorWrestling written at 23:15:18; Add Comment

2018-08-06

Link: Where Vim Came From

Where Vim Came From (via) is an interesting and thorough overview of the history of vim, vi, ed, and other predecessors (with copious footnotes). It's nice to see all of the pieces laid out this way, and I learned of some historical links that I hadn't already known.

(I do wonder what vi would have been like if ed had kept QED's multiple buffer support.)

Update, the next day: See also Dennis Ritchie's An incomplete history of the QED Text Editor (via).

VimWhereFrom written at 22:00:01; Add Comment

2018-06-13

Link: A Child’s Garden of Inter-Service Authentication Schemes

A Child’s Garden of Inter-Service Authentication Schemes is an opinionated overview of service to service authentication schemes from Latacora (via, which has comments worth reading for once, including from various Latacora people). As with pretty much everything Latacora writes on their blog, it's not just informative, it's entertaining too. I find it well worth reading.

(Latacora people include Thomas Ptacek, who you may remember from Against DNSSEC.)

InterServiceAuthGarden written at 22:15:11; Add Comment

Link: About the memory management in the Bourne shell

About the memory management in the Bourne shell (via) is a collection of discussions about the original Bourne shell's creative, interesting, and infamous approach to memory management in the original Unix memory allocation scheme. If you like this kind of thing, it's worth reading through and decoding things.

(It also links to a recording of Stephen Bourne's BSDCan 2015 talk "Early days of Unix and design of sh", which I haven't watched yet but keep seeing links to. Someday.)

BourneMemoryManagement written at 13:52:06; Add Comment

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