This Week In Security: GhostWrite, Localhost, And More

August 9, 2024 by Jonathan Bennett 5 Comments

You may have heard some scary news about RISC-V CPUs. There’s good news, and bad news, and the whole thing is a bit of a cautionary tale. GhostWrite is a devastating vulnerability in a pair of T-Head XuanTie RISC-V CPUs. There are also unexploitable crashes in another T-Head CPU and the QEMU soft core implementation. These findings come courtesy of a group of researchers at the CISPA Helmholtz Center for Information Security in Germany. They took at look at RISC-V cores, and asked the question, do any of these instructions do anything unexpected? The answer, obviously, was “yes”.

Undocumented instructions have been around just about as long as we’ve had Van Neumann architecture processors. The RISC-V ISA put a lampshade on that reality, and calls them “vendor specific custom ISA extensions”. The problem is that vendors are in a hurry, have limited resources, and deadlines wait for no one. So sometimes things make it out the door with problems. To find those problems, CISPA researchers put together a test framework is called RISCVuzz, and it’s all about running each instruction on multiple chips, and watching for oddball behavior. They found a couple of “halt-and-catch-fire” problems, but the real winner (loser) is GhostWrite.

Now, this isn’t a speculative attack like Meltdown or Spectre. It’s more accurate to say that it’s a memory mapping problem. Memory mapping helps the OS keep programs independent of each other by giving them a simplified memory layout, doing the mapping from each program to physical memory in the background. There are instructions that operate using these virtual addresses, and one such is vs128.v. That instruction is intended to manipulate vectors, and use virtual addressing. The problem is that it actually operates directly on physical memory addresses, even bypassing cache. That’s not only memory, but also includes hardware with memory mapped addresses, entirely bypassing the OS. This instruction is the keys to the kingdom. Continue reading “This Week In Security: GhostWrite, Localhost, And More” →

Liquid (Reversibly) Solidifies At Room Temperature, Gets Used For 3D Prints

August 9, 2024 by Donald Papp 8 Comments

Researchers demonstrate sustainable 3D printing by using poly(N-isopropylacrylamide) solutions (PNIPAM), which speedily and reliably turn solid by undergoing a rapid phase change when in a salt solution.

This property has been used to 3D print objects by using a syringe tip as if it were a nozzle in a filament-based printer. As long as the liquid is being printed into contact with a salt solution, the result is a polymer that solidifies upon leaving the syringe.

What’s also interesting is that the process by which the PNIPAM-based solutions solidify is entirely reversible. Researchers demonstrate printing, breaking down, then re-printing, which is an awfully neat trick. Finally, by mixing different additives in with PNIPAM, one can obtain different properties in the final product. For example, researchers demonstrate making conductive prints by adding carbon nanotubes.

While we’ve seen the concept of printing with liquids by extruding them into a gel bath or similar approach, we haven’t seen a process that prides itself on being so reversible before. The research paper with all the details is available here, so check it out for all the details.

Fixing A Busted Fluke While Fighting A Wonky Schematic

August 9, 2024 by Dan Maloney 16 Comments

Fluke meters have been around for a long, long time. Heck, we’ve got a Fluke 73 that we bought back in 1985 that’s still a daily driver. But just because they’ve been making them forever doesn’t mean they last forever, and getting a secondhand meter back in the game can be a challenge. That’s what [TheHWCave] learned with his revival of a wonky eBay Fluke 25, an effort that holds lessons for anyone in the used Fluke market.

Initial inspection of the meter showed encouragingly few signs of abuse, somewhat remarkable for something built for the military in the early 1980s. A working display allowed a few simple diagnostics revealing that the ammeter functions seemed to work, but not the voltmeter and ohmmeter functions. [TheHWCave]’s teardown revealed a solidly constructed unit with no obvious signs of damage or blown fuses. Thankfully, a service schematic was available online, albeit one with a frustrating lack of detail, confusing test point nomenclature, and contradictory component values.

Despite these hurdles, [TheHWCave] was able to locate the culprit: a bad fusible power resistor. Finding a direct replacement wasn’t easy given the vagaries of the schematic and the age of the instrument, but he managed to track down a close substitute cheap enough to buy in bulk. He searched through 40 units to find the one closest to the listed specs, which got the meter going again. Fixing the bent pin also gave the meter back its continuity beeper, always a mixed blessing.

If you’re in the market for a meter but can’t afford the Fluke name, picking up a busted meter and fixing it up like this might be one way to go. But are they really worth the premium? Well, kinda yes.

Continue reading “Fixing A Busted Fluke While Fighting A Wonky Schematic” →