linux

630 Articles

Go Retro To Build A Spectre And Meltdown-Proof X86 Desktop

January 7, 2018 by 95 Comments

[Yeo Kheng Meng] had a question: what is the oldest x86 processor that is still supported by a modern Linux kernel? Furthermore, is it actually possible to use modern software with this processor? It’s a question that surely involves experimentation, staring into the bluescreen abyss of BIOS configurations, and compiling your own kernel. Considering Linux dropped support for the 386 in 2012, the obvious answer is a 486. This supposition was tested, and the results are fantastic. You can, indeed, install a modern Linux on an ancient desktop.

This project got its start last month at a Super Silly Hackathon where [Yeo] and [Hui Jing] installed Damn Small Linux on an ancient IBM PS/1 desktop of 1993 vintage. The hardware consists of an AMD 486 clone running at 133MHz, 64 MB of RAM, a 48x IDE CDROM drive (wow!), a floppy emulator, a Sound Blaster, 10Mbps Ethernet card, and a CompactFlash to IDE adapter. By any account, this is a pimped-out rig for 1993 that would have cost more than a car at the time. The hardware works, but can you run a modern Linux kernel on it?

[Yeo] decided to install the Gentoo x86 minimal installation, but sanity and time constraints meant compiling a kernel on a 486 wasn’t happening. That was done on a modern Thinkpad after partitioning all the drives, verifying all the compilation parameters, and configuring the kernel itself. The bootloader is LILO (Grub2 didn’t work), but for the most part, this is entirely modern software running on a 25-year-old machine. The step-by-step instructions for becoming a /g/entooman on a 486 are available on GitHub.

The entire (boring) boot process can be seen in the video below. One interesting application of this build is that the 486 does not support out-of-order execution, making this completely safe from Meltdown and Spectre attacks. It’s an impressive retrocomputing achievement that right now could not be more timely.

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Learn To Reverse Engineer X86_64 Binaries

January 6, 2018 by 16 Comments

Opening up things, see how they work, and make them do what you want are just the basic needs of the average hacker. In some cases, a screwdriver and multimeter will do the job, but in other cases a binary blob of random software is all we have to work with. Trying to understand an unknown binary executable is an exciting way to discover a system’s internal functionality.

While the basic principles of software reverse engineering are universal across most platforms, the details can naturally vary for different architectures. In the case of the x86 architecture, [Leonora Tindall] felt that most tutorials on the subject focus mostly on 32-bit and not so much on the 64-bit specifics. Determined to change that, she ended up with an extensive introduction tutorial for reverse engineering x86_64 binaries starting at the very basics, then gradually moving forward using crackme examples. Covering simple string analysis and digging through disassembled binaries to circumvent fictional security, the tutorial later introduces the Radare2 framework.

All example source code is provided in the accompanying GitHub repository, although it is advised to avoid looking at them to keep it more interesting and challenging. And in case you are looking for more challenges later on, or generally prefer a closer connection to the hardware, these MSP430 based capture the flag online challenges might be worth to look at next.

Fixing Linux Audio One Chipset At A Time

November 25, 2017 by 34 Comments

Linux audio may be confusing for the uninitiated. As a system that has evolved and spawned at least two independent branches over time it tends to produce results that surprise or irritate the user. On the other hand it is open source software and thus can be fixed if you know what you do.

Over at reddit [rener2] was annoyed by the fact that listening to music on his laptop was a significantly worse experience under Linux than under Windows. Running Windows the output of  the headphone jack covered the whole spectrum while his Linux set up cut off the low end resulting in a tinny sound. The culprit in this is the sound card: it has two different output paths for the internal speakers and the headphone jack. The signal for the internal speakers is routed through a high pass filter to spare them the embarrassment of failure to reproduce low frequencies.

When headphones are plugged in, the sound card driver is supposed to make the sound card bypass the filter and deliver the full spectrum. The authors of the Windows driver knew this and had it taken care of. In his video [rener2] runs us through the process of patching the ALSA driver while referencing the documentation of a sound card that he deems ‘similar enough’ to his Realtek ALC288.

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Turn Command Lines Into Web Apps

November 19, 2017 by 15 Comments

Even if you like using a graphical user interface, you can probably agree that writing a graphical program is usually harder than writing an old-fashioned text-based program. Putting that GUI into an online format means even more to think about. [Adam Kewley] has the answer to that problem: Jobson. As you can see in the video below, the program is a web server that runs command line programs as jobs.

Simply write a YAML file to describe the program’s inputs and outputs and Jobson will create input fields for arguments and display the output in a web page. Any files the program creates are available to download. Basically any command line program can be quickly and easily pulled into one web interface to rule them.

If a program takes a long time to run, Jobson will let you switch away and then later resume looking at the output. You can also abort a job or look at the arguments it received. Jobson can also authenticate users with several different methods to prevent just anyone from executing jobs.

If you really want to write a graphical program, try QTCreator. Or, you can get a shell in a web browser if you want to go that route. But this is the smoothest method we’ve seen for gathering command line programs into one place for monitoring and control. Neat!

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Linux Fu: System Administration Made Easier

November 9, 2017 by 47 Comments

Linux can have a somewhat split personality. If you use it as a desktop OS, it has a lot of GUI tools, although sometimes you still need to access the command line. If you use it as a headless server, though, you probably ought to know your way around the command line pretty well. This is especially true if you don’t want to litter up your hard drive (and CPU) with X servers and other peculiarities of the graphical user interface.

Personally, I like the command line, but I am realistic enough to know that not everyone shares that feeling. I’ll also admit that for some tasks — especially those you don’t do very often — it is nice to have some helpful buttons and menus. There are several administration tools that you might be interested in using to handle administration tasks on your Linux machines. I’m going to look at two of them you might want to experiment with that both use a Web browser to provide their interface.

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What Is Entropy And How Do I Get More Of It?

November 2, 2017 by 55 Comments

Let’s start off with one of my favorite quotes from John von Neumann: “Any one who considers arithmetical methods of producing random digits is, of course, in a state of sin. For, as has been pointed out several times, there is no such thing as a random number — there are only methods to produce random numbers, and a strict arithmetic procedure of course is not such a method.”

What von Neumann is getting at is that the “pseudo” in pseudorandom number generator (PRNG) is really a synonym for “not at all”. Granted, if you come in the middle of a good PRNG sequence, guessing the next number is nearly impossible. But if you know, or can guess, the seed that started the PRNG off, you know all past and future values nearly instantly; it’s a purely deterministic mathematical function. This shouldn’t be taken as a rant against PRNGs, but merely as a reminder that when you use one, the un-guessability of the numbers that it spits out is only as un-guessable as the seed. And while “un-guessability” isn’t a well-defined mathematical concept, or even a real word, entropy is.

That’s why entropy matters to you. Almost anything that your computer wants to keep secret will require the generation of a secret random number at some point, and any series of “random” numbers that a computer generates will have only as much entropy, and thus un-guessability, as the seed used. So how does a computer, a deterministic machine, harvest entropy for that seed in the first place? And how can you make sure you’ve got enough? And did you know that your Raspberry Pi can be turned into a heavy-duty source of entropy? Read on!

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SiFive Announces RISC-V SoC

October 4, 2017 by 33 Comments

At the Linley Processor Conference today, SiFive, the semiconductor company building chips around the Open RISC-V instruction set has announced the availability of a quadcore processor that runs Linux. We’ve seen RISC-V implementations before, and SiFive has already released silicon-based on the RISC-V ISA. These implementations are rather small, though, and this is the first implementation designed for more than simple embedded devices.

This announcement introduces the SiFive U54-MC Coreplex, a true System on Chip that includes four 64-bit CPUs running at 1.5 GHz. This SoC is built with TSMC’s 28 nm process, and fits on a die about 30 mm². Availability will be on a development board sometime in early 2018, and if our expectations match the reality of SiFive’s previous offerings, you’ll be able to buy this Open SoC as a BGA package some months after that.

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