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CPU Usage Differences After Applying Meltdown Patch at Epic Games

epicgames.com

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Re: CPU Usage Differences After Applying Meltdown Patch at Epic Games

#101
post #71

The Meltdown attack requires an attacker to have a piece of code executed on your server. Epic's servers are used for login, where people send you data, and for game logic, where people also just send you data like "player x moved his avatar here, player y shoots etc". If all the server does is execute the code which Epic wrote themselves and already trust, why would it need to apply the Meltdown patch?

I assume their servers will he running untrusted Unreal Engine games, maybe even community-developed mods, some of which may have attacks in the script of the game.

Re: CPU Usage Differences After Applying Meltdown Patch at Epic Games

#103
post #71

The Meltdown attack requires an attacker to have a piece of code executed on your server. Epic's servers are used for login, where people send you data, and for game logic, where people also just send you data like "player x moved his avatar here, player y shoots etc". If all the server does is execute the code which Epic wrote themselves and already trust, why would it need to apply the Meltdown patch?

This is a horrible approach to security. If you only secure against attacks you expect, you're gonna have a bad time.

[deleted]

Re: CPU Usage Differences After Applying Meltdown Patch at Epic Games

#104

I know they don't have to share the details, but the "patched" part is not really clear. Did they update to a new image / more recent kernel / anything else? Much like the redis post linked in HN before, we don't know if the impact is because of the "pti turned off/on" change, or are there more moving parts involved.

Agreed. No detail on what they're running. Ubuntu fixes aren't out yet, so this is early data which is super useful - if we knew what system this is.

Re: CPU Usage Differences After Applying Meltdown Patch at Epic Games

#105

Pretty much what I predicted here: https://news.ycombinator.com/item?id=16054674 > Sounds like servers handling lots of small UDP packets would be hit pretty hard.

Fortnite doesn’t use UDP at all (80, 443 and 5222 all TCP), UE4 uses TCP for its network stack by default.

Re: CPU Usage Differences After Applying Meltdown Patch at Epic Games

#107
post #94
post #82

Earlier quoted context omitted.

It makes sense if you don't want a remote code execution in one of your app to provide a full root shell.

Thank you for the explanation, and especially for being non-snarky, which unfortunately seems to be getting rarer and rarer on this forum.

> which unfortunately seems to be getting rarer and rarer on this forum.

If this isn't unnecessarily "snarky" itself, then what is it?

snarky: (of a person, words, or a mood) sharply critical; cutting; snide.

Re: CPU Usage Differences After Applying Meltdown Patch at Epic Games

#108
post #106

Maybe off-topic: Is formal verification viable anywhere in CPU logic design? Also, could any existing "CPU static analyzers" have caught the issue that caused Meltdown? Edit: It looks like the answer to the first is a definite yes.

Not until we have a fully accurate theory of physics and perfect models for the CPUs.

Re: CPU Usage Differences After Applying Meltdown Patch at Epic Games

#110
post #106

Maybe off-topic: Is formal verification viable anywhere in CPU logic design? Also, could any existing "CPU static analyzers" have caught the issue that caused Meltdown? Edit: It looks like the answer to the first is a definite yes.

Formal verification of what?

You can only verify properties you've thought of, and no-one conceived of this particular 'feature' causing issues like this until now. So I don't think formal verification would have helped: if anyone was in a position to realise the issue was worth verifying, they'd have been able to raise it without formal verification too.

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