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Episode #880 Quiz

RetBleed
Date: 2022-07-19 | Length: 1.75 hrs | Episode page at twit.tv

About this episode

RetBleed exploits speculative execution by abusing return instructions and branch predictor state to leak arbitrary kernel memory on patched Intel and AMD systems. ETH Zurich reverse engineered microarchitectural conditions, bypassing retpoline mitigations via branch target injection. Linux and cloud vendors shipped fixes, but affected CPUs may suffer 14–39% performance losses.

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Question 1: According to the episode, which combination of processors and branch-prediction mechanism made RetBleed possible despite retpoline being deployed as a Spectre Variant 2 mitigation?

Question 1

According to the episode, which combination of processors and branch-prediction mechanism made RetBleed possible despite retpoline being deployed as a Spectre Variant 2 mitigation?

Speculative loads under privilege-boundary conditions and the branch history table Return instructions under certain microarchitecture-dependent conditions and the Return Stack Buffer Synchronized interrupts under kernel preemption and the reorder buffer Indirect jumps under cache-independent conditions and the Translation Lookaside Buffer

Question 2: What throughput and accuracy did the episode report for RetBleed on AMD Zen 2 chips?

Question 2

What throughput and accuracy did the episode report for RetBleed on AMD Zen 2 chips?

390 bytes per second with 99% accuracy 3900 bytes per second with greater than 99% accuracy 2190 bytes per second with greater than 90% accuracy 219 bytes per second with 98% accuracy

Question 3: Which Linux kernel response did Steve say was triggered by the RetBleed disclosure?

Question 3

Which Linux kernel response did Steve say was triggered by the RetBleed disclosure?

Linus froze all development until the next quarter Linus reverted all June security fixes from 5.19 Linus removed retpoline support from the tree Linus delayed the next release by one week

Question 4: Which set of processors did the ETH Zurich researchers say they tested and found likely affected by RetBleed?

Question 4

Which set of processors did the ETH Zurich researchers say they tested and found likely affected by RetBleed?

AMD FX, Ryzen Mobile, and Intel Core 2 through 5 AMD Zen 3, Zen 4, and Intel Core 9, 10, 11 AMD EPYC only and Intel Atom only AMD Zen 1, Zen 1+, Zen 2, and Intel Core 6, 7, 8

Question 5: What performance impact did the episode say the RetBleed mitigations could have on affected processors, and what AMD-only issue might be even worse?

Question 5

What performance impact did the episode say the RetBleed mitigations could have on affected processors, and what AMD-only issue might be even worse?

5% to 10%, with Phantom JMPs reaching 120% 40% to 60%, with Phantom JMPs reaching 90% 1% to 4%, with Phantom JMPs reaching 29% 14% to 39%, with Phantom JMPs reaching 209%

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