T2 Linux Discovers (Now Patched) AMD Zen 4 Invalid Opcode Speculation Bug

T2 SDE is not just a Linux distribution, but "a flexible Open Source System Development Environment or Distribution Build Kit," according to a 2022 announcement of its support for 25 CPU architectures, variants, and C libraries. ("Others might even name it Meta Distribution. T2 allows the creation of custom distributions with state of the art technology, up-to-date packages and integrated support for cross compilation.")

And while working on it, Berlin-based T2 Linux developer René Rebe (long-time Slashdot reader ReneR) discovered random illegal instruction speculation on AMD Ryzen 7000-Series and Epyc Zen 4 CPU.

ReneR writes:

Merged to Linux 6.6 Git is a fix for the bug now known at AMD as Erratum 1485.

The discovery was possible through continued high CPU load cross-compiling the T2 Linux distribution with support for all CPU architectures from ARM, MIPS, PowerPC, RISC-V to x86 (and more) for 33 build variants. With sustained high CPU load and various instruction sequences being compiled, pseudo random illegal instruction errors were observed and subsequently analyzed.

ExactCODE Research GmbH CTO René Rebe is thrilled that working with AMD engineers lead to a timely mitigation to increase system stability of the still new and highest performance Zen4 platform.


"I found real-world code that might be similar or actually trigger the same bugs in the CPU that are also used for all the Spectre Meltdown and other side-channel security vulnerability mitigations," Rebe says in a video announcement on YouTube.

It took Rebe a tremendous amount of research, and he says now that "all the excessive work changed my mind. Mitigations equals considered harmful... If you want stable, reliable computational results — no, you can't do this. Because as Spectre Meltdown and all the other security issues have proven, the CPUs are nowadays as complex as complex software systems..."

Read more of this story at Slashdot.