Take A Way: Exploring the Security Implications of AMD's Cache Way Predictors

Moritz Lipp, Vedad Hadzic, Michael Schwarz, Arthur Perais, Clementine Lucie Noemie Maurice, Daniel Gruß

Research output: Chapter in Book/Report/Conference proceedingConference paperpeer-review


To optimize the energy consumption and performance of their CPUs, AMD introduced a way predictor for the L1-data (L1D) cache to predict in which cache way a certain address is located. Consequently, only this way is accessed, significantly reducing the power consumption of the processor.
In this paper, we are the first to exploit the cache way predictor. We reverse-engineered AMD’s L1D cache way predictor in microarchitectures from 2011 to 2019, resulting in two new attack techniques. With Collide+Probe, an attacker can monitor a victim’s memory accesses without knowledge of physical addresses or shared memory when time-sharing a logical core. With Load+Reload, we exploit the way predictor to obtain highly-accurate memory-access traces of victims on the same physical core. While Load+Reload relies on shared memory, it does not invalidate the cache line, allowing stealthier attacks that do not induce any last-level-cache evictions.
We evaluate our new side channel in different attack scenarios. We demonstrate a covert channel with up to 588.9 kB/s, which we also use in a Spectre attack to exfiltrate secret data from the kernel. Furthermore, we present a key-recovery attack from a vulnerable cryptographic implementation. We also show an entropy-reducing attack on ASLR of the kernel of a fully patched Linux system, the hypervisor, and our own address space from JavaScript. Finally, we
propose countermeasures in software and hardware mitigating the presented attacks.
Original languageEnglish
Title of host publicationProceedings of the 15th ACM Asia Conference on Computer and Communications Security, ASIA CCS 2020
Place of PublicationNew York, NY
PublisherAssociation of Computing Machinery
Number of pages13
ISBN (Electronic)978-1-4503-6750-9
Publication statusPublished - 5 Oct 2020
Event15th ACM ASIA Conference on Computer and Communications Security: AsiaCCS 2020 - Virtuell
Duration: 5 Oct 20209 Oct 2020


Conference15th ACM ASIA Conference on Computer and Communications Security
Abbreviated titleAsiaCCS 2020:


  • Side-channel attack
  • way predictor
  • side-channel attacks
  • way prediction

ASJC Scopus subject areas

  • Software
  • Computer Networks and Communications

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