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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.”

#71

Post by nabla9 »

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?

All instructions that decode into more than four micro-ops still go trough microcode. Typically 5% of micro-ops are still coming from the microcode sequencer even in modern architectures.

Compiler has large effect. Common operations like CALL and PUSH go trough microcode even in m64 but there are alternatives. Many floating point operations have assists. Nonoptimal memory alignment might go trough microcode.

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

#72

Post by jnordwick »

aidenn0 wrote: post #65
jnordwick wrote: post #57

Earlier quoted context omitted.

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…

Meltdown is almost trivial to take advantage of, as these things go, and it was discovered independently by more than one researcher. That makes it somewhat more likely to have been exploited by a government level attacker. However, just being able to read all of kernelspace is more of a force-multiplier than being useful on its own. You still need to get your code executing in user-space to do anything, ant it's val…

Trivial, yet nobody has managed to produce a working exploit that doesn't require a running start. The poc exploits wouldn't work in the wild. They are running with interference of a real system.

Also, meltdown requires the data to be snooped to be in L1D cache. So the current demo exploit has to keep pushing the data into cache to be read.

Something simple like steal a password from sudo should be trivia right? I'd not convinced i need to worry.

And making non public facing machines pay the price of the mitigation seems like too much.

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

#73

Post by adrian17 »

gambiting wrote: post #35

Am I the only person who finds this extremely difficult to read? The top says "David wrote" and then it looks like he's replying to a message from Linus Torvalds. So any quoted text is by Linus, right? But then....the letter is signed by Linus? So who wrote it? I know this is some ancient technology but Jesus, the user interface is horrendous.

Well, "modern" technology does this too; Markdown quoting on many sites works exactly like that - the only difference is that mailing lists prefer not prettifying messages. This email would look like this if copied directly to Reddit (and GitHub):

https://i.imgur.com/eXODVHb.png

(which also reminds me of how Tumblr's reblogs look: https://i.imgur.com/e6UR8bn.png)

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

#74

Post by nolok »

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.

Big simplification:

Proper way to fix an hardware bug like this, is that newer cpu gets protected by default, and they answer they are when queried.

So you can ask the CPU "what's your status on bug X" and the cpu answers "i'm good, you don't need to do anything" (newer fixed chips), or "i know about it but was already built, and need microcode update/special behavior to protect myself" (current chips with microcode update), "no answer / I'm not good" (old chips without update).

So new stuff is protected, and you add more protection (and slowdowns, and special stuff) for older chips that don't know how to deal with it.

What Intel is trying to do here, is to go the other way: the chips, even the new ones, will stay vulnerable by default, and when queried they say "I have a fix but I don't use it, you can enable it by asking !" and the kernel is supposed to enable it.

It's terrible for a lot of reasons, like "boot an older os and it's vulnerable since it doesn't know to call this", "additional code to enable this feature has to run for all of eternity for new chips now, instead of having to run for older chips and being phased out over time", etc ...

The reason why Intel does that seems obvious: by default the chip does not lose speed since the fix is not enabled, and so instead of "intel chips lose 30% speed over night because of a flaw" it becomes "intel adds a special security mode that protects you even more for critical applications, at the cost of some speed". Purely marketing speech and decision at the cost of proper engineering decisions, and they need and try to get OSes like Linux to play along. That's what he means by "[it] shows intel had no intention of fixing those flaws".

Additionally there seems to be a second issue in that the quality and behavior of the patches they submitted are trying to hide this deceptively simple but technically terrible behavior by making it look/sound obtuse and complicated.

In other words, intel is using its presence and weight to try and push a shitty solution, but one that is better for them marketing wise. Linus is flabbergasted to be treated like an idiot or a obedient drone that should apply such obvious abusive patches.

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

#75

Post by dang »

chrisper wrote: post #29

Whoever changed the title managed to make it less clear. With "Linus" in the title it was clear that it was Linux.

I did that. We've observed over the years that celebrity names in titles tend to make for poorer discussion. HN is better when the focus is on content rather than personalities.

https://hn.algolia.com/?sort=byDate&dateRange=all&type=comme...

Edit: ok, you guys have convinced me that this is a special case and we've put Linus back in the title above.

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

#76

Post by ryanlol »

walterbell wrote: post #69
Animats wrote: post #31

Well, Torvalds has been heard from, along with Bloomberg and The Economist, as saying that Intel is in denial about this being a big, big problem.

Has a major technology media outlet taken a similar position as Bloomberg and The Economist?

Are there any people who care about what the “technology media” says?

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

#77

Post by beebmam »

Really abusive language. There are ways to communicate his objections to the patches with extremely strong language WITHOUT resorting to abusive language.

I wouldn't tolerate anyone treating me like this. There are unseen consequences to a wild tongue.

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

#78

Post by Valmar »

dang wrote: post #75
chrisper wrote: post #29

Whoever changed the title managed to make it less clear. With "Linus" in the title it was clear that it was Linux.

I did that. We've observed over the years that celebrity names in titles tend to make for poorer discussion. HN is better when the focus is on content rather than personalities. https://hn.algolia.com/?sort=byDate&dateRange=all&type=comme... Edit: ok, you guys have convinced me that this is a special case and we've put Linus back in the title above.

Good to know. :)

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

#79

Post by sannee »

teekert wrote: post #28

Why doesn't Intel just go to Linus and ask politely: "Ok, we f-ed up, here is a million dollars (or whatever, 10x his normal salary or something) can you please work with us tightly for some time? Thank you." I would really respect Intel if they would.

Note that Intel is a platinum member of the Linux Foundation, which means they donate >=500k$ per year.

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

#80

Post by AstralStorm »

aidenn0 wrote: post #65
jnordwick wrote: post #57

Earlier quoted context omitted.

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…

Meltdown is almost trivial to take advantage of, as these things go, and it was discovered independently by more than one researcher. That makes it somewhat more likely to have been exploited by a government level attacker. However, just being able to read all of kernelspace is more of a force-multiplier than being useful on its own. You still need to get your code executing in user-space to do anything, ant it's val…

On the other hand, Spectre would mostly matter for crypto side channel attacks - to extract timings from poorly written crypto code.
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