[flagged]
You know how it is in social media -- just like in academia: "Publish or perish".
Mitigations=off considered harmful or spurious SIGILL on AMD Zen4
21–30 of 47 posts
Re: Mitigations=off considered harmful or spurious SIGILL on AMD Zen4
#22[flagged]
Someone got an axe to grind.
Re: Mitigations=off considered harmful or spurious SIGILL on AMD Zen4
#23Earlier quoted context omitted.
Some state being in the CPU or kernel? I guess if you have per core state in the kernel that's only accessed by that core, then you're safe to modify it without locking, but this isn't the case for data shared between hyperthreads of a core?
Within the CPU core (terminology here gets awkward). Spectre in its simplest to exploit form used the fact that the branch prediction based state wasn't completely cleared between running different threads on the CPU and led to a really easy timing attack. Time your own code to see which way the branch of the previous code likely went. There's a lot of CVE's around this but that's the simplest case. The mitigations w…
Is it likely the issue is within the Linux kernel itself or within the microcode for the CPU?
Re: Mitigations=off considered harmful or spurious SIGILL on AMD Zen4
#24Re: Mitigations=off considered harmful or spurious SIGILL on AMD Zen4
#25Earlier quoted context omitted.
Within the CPU core (terminology here gets awkward). Spectre in its simplest to exploit form used the fact that the branch prediction based state wasn't completely cleared between running different threads on the CPU and led to a really easy timing attack. Time your own code to see which way the branch of the previous code likely went. There's a lot of CVE's around this but that's the simplest case. The mitigations w…
Is it likely the issue is within the Linux kernel itself or within the microcode for the CPU?
[deleted]
Re: Mitigations=off considered harmful or spurious SIGILL on AMD Zen4
#26Interesting walk through in the linked video as he tried to troubleshoot this: https://www.youtube.com/live/1UnoBfw6soI Pretty shocking to see (extremely unlikely) non-malicious code work / not-work depending on a security mitigation setting. Curious to see where this goes as to whether it's a kernel bug and nobody is paying attention to `mitigations=off` now or the unlikely outcome that it's an actual hardware bug w…
Mitigations can have very large effects on system stability, I ran into this with my old Haswell system. Mitigations on allowed, I believe, 100Mhz higher at lower voltage - but it may have been 200Mhz. These settings were tested over many months, completely stable, and mitigations off with the same setting wouldn't even allow booting. Huge effect relative to anything else, basically like adding an extra 0.1V vcore.
Re: Mitigations=off considered harmful or spurious SIGILL on AMD Zen4
#27Earlier quoted context omitted.
Within the CPU core (terminology here gets awkward). Spectre in its simplest to exploit form used the fact that the branch prediction based state wasn't completely cleared between running different threads on the CPU and led to a really easy timing attack. Time your own code to see which way the branch of the previous code likely went. There's a lot of CVE's around this but that's the simplest case. The mitigations w…
Is it likely the issue is within the Linux kernel itself or within the microcode for the CPU?
[deleted]
Re: Mitigations=off considered harmful or spurious SIGILL on AMD Zen4
#28Interesting walk through in the linked video as he tried to troubleshoot this: https://www.youtube.com/live/1UnoBfw6soI Pretty shocking to see (extremely unlikely) non-malicious code work / not-work depending on a security mitigation setting. Curious to see where this goes as to whether it's a kernel bug and nobody is paying attention to `mitigations=off` now or the unlikely outcome that it's an actual hardware bug w…
What does he say at 8:17?[1] Arsink Overism?
[1]: https://www.youtube.com/live/1UnoBfw6soI?si=R8nJ1FxdE4zBuO0i...
Re: Mitigations=off considered harmful or spurious SIGILL on AMD Zen4
#29Have they tested this on more than one machine? This seems like it could be a hardware fault
[deleted]
Re: Mitigations=off considered harmful or spurious SIGILL on AMD Zen4
#30I am reminded of this article several years ago remarking on Intel's CPU bugs: https://news.ycombinator.com/item?id=16058920
Perhaps AMD has also gone down the same path. It's unfortunate that the hardware industry has also formalised planned obsolescence ("end of life" and similar phrasings) which drastically decreases the motivation to achieve perfection, as they can then defer "fixing" anything to "buy the new model" (complete with its own, unknown, new set of bugs...)