Reorder Buffer Contention : A Forward Speculative Interference Attack for Speculation Invariant Instructions

• Speculative side-channel attacks access sensitive data and use transmitters to leak the data during wrong-path execution. Various defenses have been proposed to prevent such information leakage. However, not all speculatively executed instructions are unsafe: Recent work demonstrates that speculation invariantinstructions are independent of speculative control-flow paths and are guaranteed to eventually commit, regardless of the speculation outcome. Compile-time information coupled with run-time mechanisms can then selectively lift defenses for speculation invariant instructions, reclaiming some of the lost performance. Unfortunately, speculation invariant instructions can easily be manipulated by a form of speculative interference to leak information via a new side-channel that we introduce in this paper. We show that forward speculative interference where older speculative instructions interfere with younger speculation invariant instructions effectively turns them into transmitters for secret data accessed during speculation. We demonstrate forward speculative interference on actual hardware, by selectively filling the reorder buffer (ROB) with instructions, pushing speculative invariant instructions in-or-out of the ROB on demand, based on a speculatively accessed secret. This reveals the speculatively accessed secret, as the occupancy of the ROB itself becomes a new speculative side-channel.

Subject headings

NATURVETENSKAP  -- Data- och informationsvetenskap -- Datavetenskap (hsv//swe)

NATURAL SCIENCES  -- Computer and Information Sciences -- Computer Sciences (hsv//eng)

TEKNIK OCH TEKNOLOGIER  -- Elektroteknik och elektronik -- Datorsystem (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Electrical Engineering, Electronic Engineering, Information Engineering -- Computer Systems (hsv//eng)

Keyword

Interference

Transmitters

Hardware

Microarchitecture

Delays

Side-channel attacks

Program processors

Speculative side-channel attacks

security

spectre

speculative interference

Publication and Content Type

ref (subject category)

art (subject category)