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Linus Torvalds: “Somebody is pushing complete garbage for unclear reasons.”

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Re: Linus Torvalds: “Somebody is pushing complete garbage for unclear reasons.”

#51

Post by Johnny555 »

dingo_bat wrote: post #15

I'm going to be honest, I need an ELI5 here. I know what the meltdown/spectre issues are, and kinda understand what retpoline is.

Here's an explanation of retpoline:

https://support.google.com/faqs/answer/7625886

“Retpoline” sequences are a software construct which allow indirect branches to be isolated from speculative execution. This may be applied to protect sensitive binaries (such as operating system or hypervisor implementations) from branch target injection attacks against their indirect branches.

The name “retpoline” is a portmanteau of “return” and “trampoline.” It is a trampoline construct constructed using return operations which also figuratively ensures that any associated speculative execution will “bounce” endlessly.

Re: Linus Torvalds: “Somebody is pushing complete garbage for unclear reasons.”

#52

Post by watwut »

akira2501 wrote: post #32
yborg wrote: post #5

Run through the Linus drama filter, the only thing I get from this is "Linus doesn't like the Meltdown/Spectre patches'; Linus having issues with a patch is, well, not particularly newsworthy. Is there something more significant here than a bad first go at this?

> Linus having issues with a patch is, well, not particularly newsworthy. Why not? The lead engineer of the linux kernel project has specific issues with security patches from a major hardware vendor. I understand the constant distaste that some users here have with Linus' style, but I don't understand the constant need to denigrate his positions by attempting to paint them as particularly diminutive.

It is patch from Amazon, not from hardware vendor.

Re: Linus Torvalds: “Somebody is pushing complete garbage for unclear reasons.”

#53

Post by Sephr »

Animats wrote: post #33
Valmar wrote: post #14

Earlier quoted context omitted.

Said current patches haven't been merged. Just posted to the mailing list for review. Retpolines for Spectre, and PTI for Meltdown, are still in the kernel. Linus doesn't have too much disagreement with them. It's the IBRS / IBPB code for Intel's CPUs that Linus has a problem with. Also, not everything can be mitigated in microcode, for many reasons, not all of which I understand myself. Sometimes, only a fundamental…

Well, for one thing, modern CPUs aren't microcoded much. Real microcoded CPUs went out with the 1980s. The microcode in today's fast CPUs is mostly initialization, and maybe emulation support for some instructions nobody uses any more, like decimal arithmetic or 16-bit mode. The microcode can maybe turn some stuff off and tweak some tuning parameters. Anyone know what Intel's "fixes" really do?

Microcode is a little more capable than that. See https://media.ccc.de/v/34c3-9058-everything_you_want_to_know...

Edit: s/Intel m/M/

Re: Linus Torvalds: “Somebody is pushing complete garbage for unclear reasons.”

#54

Post by Myrmornis »

akira2501 wrote: post #32
yborg wrote: post #5

Run through the Linus drama filter, the only thing I get from this is "Linus doesn't like the Meltdown/Spectre patches'; Linus having issues with a patch is, well, not particularly newsworthy. Is there something more significant here than a bad first go at this?

> Linus having issues with a patch is, well, not particularly newsworthy. Why not? The lead engineer of the linux kernel project has specific issues with security patches from a major hardware vendor. I understand the constant distaste that some users here have with Linus' style, but I don't understand the constant need to denigrate his positions by attempting to paint them as particularly diminutive.

I also have zero criticism of Linus for his style. However to be fair, the point being made by GP is I think that if the frequency of severe patch criticism by Linus is high enough ("not newsworthy"), then the information content of all his criticisms is reduced accordingly.

Re: Linus Torvalds: “Somebody is pushing complete garbage for unclear reasons.”

#55

Post by krisives »

It's upsetting that the media and some of the mainstream audience see Linus as a "crank" that only exists to complain and tear people down. Examples like this show how valuable his experience is. I would NEVER ask him to water himself down knowing it would likely make his technical analysis worse.

Re: Linus Torvalds: “Somebody is pushing complete garbage for unclear reasons.”

#56

Post by dingo_bat »

Johnny555 wrote: post #51
dingo_bat wrote: post #15

I'm going to be honest, I need an ELI5 here. I know what the meltdown/spectre issues are, and kinda understand what retpoline is.

Here's an explanation of retpoline: https://support.google.com/faqs/answer/7625886 “Retpoline” sequences are a software construct which allow indirect branches to be isolated from speculative execution. This may be applied to protect sensitive binaries (such as operating system or hypervisor implementations) from branch target injection attacks against their indirect branches. The name “retpoline” is a portmanteau of…

Maybe I wasn't clear. Your explanation and the linked article is very informative, but I wanted to understand what's the "garbage" Linus is talking about. As I said, I do understand retpolines from a high level.

Re: Linus Torvalds: “Somebody is pushing complete garbage for unclear reasons.”

#57

Post by jnordwick »

fouc wrote: post #46

Are state actors or others trying to take advantage of meltdown needing fixes & patches to insert their own version of fixes & patches that end up benefiting them?

As far as we know, there has never been a single attack using either of specter or meltdown issues. No code had been found, nothing.

It appears to be very difficult to take advantage of, and the initial idea of a JavaScript exploit seems to not be possible.

Part of the reason for all of this might be that the attacker needs to run code on the target machine, and one the attacker can do that, there are far easier ways to read memory.

Re: Linus Torvalds: “Somebody is pushing complete garbage for unclear reasons.”

#58

Post by cm2187 »

mikekchar wrote: post #40
yborg wrote: post #5

Run through the Linus drama filter, the only thing I get from this is "Linus doesn't like the Meltdown/Spectre patches'; Linus having issues with a patch is, well, not particularly newsworthy. Is there something more significant here than a bad first go at this?

I don't completely understand the technical issues, but reading between the lines I think the patches in question add super huge overhead. The overhead is so huge that nobody in their right mind would enable them by choice. However, the behaviour is governed by an opt-in configuration at boot time. What this means is that by default the patches will do nothing but if you opt in, you will get a huge performance hit. T…

But are we talking about fixing it on current chips or future chips? If the former I understand Linus’ position only if there is a better solution. But if it is a hardware problem it may not. If we are talking about future chips, I thought that the fix even on 7th and 8th generations had a low overhead. Why would it have a bigger overhead in future designs?

Re: Linus Torvalds: “Somebody is pushing complete garbage for unclear reasons.”

#59

Post by silvestrov »

dmichulke wrote: post #10
yborg wrote: post #5

Run through the Linus drama filter, the only thing I get from this is "Linus doesn't like the Meltdown/Spectre patches'; Linus having issues with a patch is, well, not particularly newsworthy. Is there something more significant here than a bad first go at this?

I interpreted it as: Intel isn't going to fix Specter in HW (as opposed to Meltdown) Instead, they do some crazy crazy black magic in the patches.

I read it like:

Intel will make a fix but the fix will be disabled by default as that results in the best performance numbers, those that will be reported in the media.

When you want to use the CPU in the cloud, you have to enable the fix and get much lower performance. But nobody in the media will care about that as they have the nice performance numbers and therefore Intel don't care to implement a fix with high performance.

Re: Linus Torvalds: “Somebody is pushing complete garbage for unclear reasons.”

#60

Post by senectus1 »

yborg wrote: post #5

Run through the Linus drama filter, the only thing I get from this is "Linus doesn't like the Meltdown/Spectre patches'; Linus having issues with a patch is, well, not particularly newsworthy. Is there something more significant here than a bad first go at this?

man, its been ages since I've read his rants... he can be such a fun keyboard warrior
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