FLUSH+RELOAD

FLUSH+RELOAD Steps

FLUSH Step

Assumptions for flushing the LLC (Last-Level Cache)

Page sharing (due, e.g., to deduplication)

Unprivileged cache flush instruction

Cache inclusiveness to prevent non-exclusive
Multilevel Caches like level 1 data is not in level 2

RELOAD Step

C volatile variable for cache inclusiveness

This code access 256 times with 4096 byte padding spacial

Cache Locality to avoid using same

Cache Line unit.

Attack Scenarios

Shared Last Level Cache (LLC) with different processor cores

Same-OS/Co-located-VM scenarios with OS/VM uses page deduplication

By observing a single signing or decryption round, the attack extracts 98.7% of the bits on average in the same OS scenario and 96.7% in the cross-VM scenario, with a worst case of 95% and 90%, respectively.

Victim Program

Assumption: there is a victim function that uses a secret value as an index to load some values from an array, as follows