Macroeconomics

Speculation

Out-of-order execution

Exploit

Speculative execution

Embedded system

Computer security

Speculative multithreading

Operating system

Branch predictor

Economics

Set (abstract data type)

Market economy

Computer science

Side channel attack

Multithreading

Hierarchy

Microarchitecture

Timing attack

Cache

Cryptography

Memory hierarchy

Programming language

Thread (computing)

State (computer science)

Speculative execution, the base on which modern high-performance general-purpose CPUs are built on, has recently been shown to enable a slew of security attacks. All these attacks are centered around a common set of behaviors: During speculative execution, the architectural state of the system is kept unmodified, until the speculation can be verified. In the event that a misspeculation occurs, then anything that can affect the architectural state is reverted (squashed) and re-executed correctly. However, the same is not true for the microarchitectural state. Normally invisible to the user, changes to the microarchitectural state can be observed through various side-channels, with timing differences caused by the memory hierarchy being one of the most common and easy to exploit. The speculative side-channels can then be exploited to perform attacks that can bypass software and hardware checks in order to leak information. These attacks, out of which the most infamous are perhaps Spectre and Meltdown, have led to a frantic search for solutions.

Efficient invisible speculative execution through selective delay and value prediction