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Comment by chris_wot | Hacker News Reader

The Linux kernel developers came up with a decent solution, how can it be that they can do this and the Microsoft developers cannot?

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Is Windows written the exact same way as Linux? Never underestimate the amount of technical debt that can be holding a team down.

It appears not, if such a bad bug can get through all the way to release.

"Linux" had a bug in which you could log into a system by pressing backspace 28 times a few years ago. And by Linux, I meant GRUB[1], and in turn, (many) Linux systems.

We're comparing Linux and Windows, an operating system that contains 3.5 million files[2] (of course, not just the kernel in this case). That isn't really fair. Code is as perfect as humans can make it, and it certainly does not help that there's so much to take into account.

[1] http://hmarco.org/bugs/CVE-2015-8370-Grub2-authentication-by...

[2] https://arstechnica.com/gadgets/2018/03/building-windows-4-m...

This GRUB bug you are talking about, is not a kernel problem though; on a side note, I'm going to read on the links you provided as I want to see if encrypted root partitions could also be compromised, I suspect no.

That's not quite on par with this Windows bug, but I take your point.

Ding-ding-ding, this is the non-bs answer.

Is that an excuse though?

The Linux kernel developers hate their solution, and they only used it because they can't think of a better one. It causes enormous increases in complexity and kills performance in many cases.

They revived previous work on this as part of the KAISER work in November 2017, and still had major bugs with it in February 2018 (ie, 4 months later). That's pretty similar to the 6 month timeline mentioned here.

https://lwn.net/Articles/738975/

https://arstechnica.com/gadgets/2018/01/whats-behind-the-int...

Linux kernel developer here. I don’t know know how MS’s Meltdown solution differs from Linux’s, let alone whether I should hate it.

MS (I think) uses IBRS to help with Spectre, and IBRS is not so great. Retpolines have a more fun name at the very least :)

I think he means Linux kernel developers hate (their own) solution for Meltdown.

The essential element of the solution for Meltdown is the same in every x86-64 OS: unmapping the kernel when in usermode. This is widely hated because it makes kernel entries and exits much slower, and blows away the TLB if your hardware doesn't have PCID support.

Yes, this.

It sucks, but what else can one do?

The Linux developers had a head start in the form of the KAISER (later KPTI) patch set, development of which had AFAIK started before Meltdown was discovered and reported in private to Intel.

>AFAIK started before Meltdown was discovered

source?

They said discovered AND reported, not just discovered. It is entirely possible someone discovered it much earlier and didn't report, but we won't ever know if evidence is never found.

According to https://googleprojectzero.blogspot.com.br/2018/01/reading-pr... Spectre was initially reported to Intel on 2017-06-01, and Meltdown a bit later.

After a quick web search, I found https://patchwork.kernel.org/patch/9712001/ which records the initial submission of the KAISER patch set at 2017-05-04. The repository at https://github.com/IAIK/KAISER has an older version of the patch set dated 2017-02-24, indicating that work on it had started even earlier.

Finally, the timeline at https://plus.google.com/+jwildeboer/posts/jj6a9JUaovP mentions a presentation from the authors of the patch set at the 33C3 on late 2016. Note that this page puts the submission of the KAISER patch set at 2017-06-24, but I believe that to be wrong; searching the web for "[RFC] x86_64: KAISER - do not map kernel in user mode" finds several mail archives with that message, and they all agree that the date was on May, not June.

That is, even if Microsoft had been immediately warned by Intel (or by Google), the Linux kernel developers would still have had a few extra months of head start, by basing their work on the KAISER patch set. Was it luck, or a side effect of the Linux kernel being used for academic research?

KAISER is developed to mitigate another less severe vulnerability.

From the meltdown paper:

> We show that the KAISER defense mechanism for KASLR [8] has the important (but inadvertent) side effect of impeding Meltdown. We stress that KAISER must be deployed immediately to prevent large-scale exploitation of this severe information leakage.

Because Linux is a completely different OS with completely different code and a completely different set of problems.

That's entirely weak.

I think the WINE people are probably looking for your help, for some reason they still seem to think there's a few differences between the two. They'll be happy to know they've been wasting their time.

Another relevant factor I just thought of: the Windows kernel has more constraints, due to binary-only drivers which have to keep working. The Linux kernel could fix any incompatible driver at the same time, since they're all in the same git tree (out-of-tree drivers are not expected to be compatible with newer kernels).

I agree. The philosophy is different. Linux is focused on having the right thing working, at the cost of compatibility (sometimes). Windows is (or at least was) focused on extreme compatibility and the actual features of operating system seem to be slapped onto the features of the previous version of the OS.

This seemed to work well for Windows audience in the past, also for Linux audience, due to the fact that they have different uses and audiences.

People seem to have segregated into those users that just want stuff working and those that want powerful operating system that allows them to do whatever they want.

At least that was until sometime the Windows 10 came...

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