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V8 Garbage Collector

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84 points swah | 1 comments | 14 Nov 25 09:53 UTC | HN request time: 0.208s | source
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ZeroConcerns ◴[14 Nov 25 11:10 UTC] No.45925770[source]▶
Interesting article! One thing that made me literally LOL was the fact that several exploits were enabled via a Google "style recommendation" that caused on-heap length fields to be signed and thus subject to sign-extension attacks.

The conversation-leading-up-to-that played out a bit like this in my head:

Google Engineer #1: Hey, shouldn't that length field be unsigned? Not like a negative value ever makes sense there?

GE#2: Style guide says no

GE#1: Yeah, but that could easily be exploited, right?

GE#2: Maybe, but at least I won't get dinged on code review: my metrics are already really lagging this quarter

GE#1: Good point! In fact, I'll pre-prepare an emergency patch for that whole thing, as my team lead indicated I've been a bit slow on the turnaround lately...

replies(2): >>45925968 #>>45925990 #
1. Leszek ◴[14 Nov 25 11:54 UTC] No.45925968[source]▶
The signed length fields pre-date the sandbox, and at that point being able to corrupt the string length meant you already had an OOB write primitive and didn't need to get one via strings. The sandbox is the new weird thing, where now these in-sandbox corruptions can sometimes be promoted into out-of-sandbox corruptions if code on the boundary doesn't handle these sorts of edge cases.