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Heat Stroke: Power-Density-Based Denial of Service in SMT. Jahangir Hasan Ankit Jalote T. N. Vijaykumar School of Electrical & Computer Engineering, Purdue University. Carla Brodley Department of Computer Science, Tufts University. Denial of Service (DOS) Attacks.

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heat stroke power density based denial of service in smt
Heat Stroke: Power-Density-Based Denial of Service in SMT

Jahangir Hasan Ankit Jalote

T. N. Vijaykumar

School of Electrical & Computer Engineering,

Purdue University

Carla Brodley

Department of Computer Science,

Tufts University

denial of service dos attacks
Denial of Service (DOS) Attacks

Resource sharing prevalent in current systems

Malicious users can exploit the sharing

DOS attacks maliciously hog shared resource

Can render the system practically inoperative

For example

Fork bomb

TCP syn flood

Can be detrimental to businesses and organizations

Must address DOS attacks to prevent financial loss

vulnerability of smt
Vulnerability of SMT

Multiple threads share pipeline resources in SMT

  • Register File
  • Cache
  • Fetch bandwidth

=> Opportunity for DOS attacks

Previously-known attacks on SMT

  • Trace Cache flushing via self-modifying code [Micro02]

Are there other unaddressed vulnerabilities?

heat stroke a novel attack in smt
Heat Stroke: A Novel Attack in SMT

Repeatedly accessing pipeline resources create hot spots

Must stall/slow down to cool

Resource shared => all threads suffer

Heat Stroke exploits this vulnerability

Persistently access shared resource at a high rate

Repeated hot-spots cause repeated slowing/stalling

Significantly degrade performance of all other threads

  • E.g., 1.2ms to heat, 12ms to cool => 90% slowdown

Must address this novel and detrimental attack

previous schemes not applicable
Previous Schemes not Applicable

Can heat stroke be solved by packaging?

  • Designed for avg. power, not local hot spots
  • Problem worsens with scaling

Can heat stroke be solved by architecture?

  • Slow down/stall entire pipeline (Clk, V Scaling)
  • They address occasional hot spots
  • But heat stroke is persistent and prolonged

Heat Stroke causes large degradation

contributions
Contributions

Identify Heat Stroke as a novel DOS attack in SMT

  • Does not exploit ICOUNT or monopolize resource
  • Purely a power-density problem

Propose Selective Sedation to address Heat Stroke

  • Identify culprit thread based on resource usage
  • Throttle only culprit thread
  • Allow other threads to continue execution

We successfully prevent Heat Stroke

key features of selective sedation
Key Features of Selective Sedation

We do not solve the general power-density problem

  • Stall only the thread having power-density problem
  • Prevent it from affecting non-problematic threads

We do not separate malicious and non-malicious

  • Doing so would be hard
  • Must stall thread if it creates hot spot, malicious or not
  • Therefore unnecessary to determine nature
overview
Overview

Introduction

Heat Stroke Examples

Our Solution to Heat Stroke

Methodology

Results

Conclusions

an example of heat stroke
An Example of Heat Stroke

Label1:

add $1, $2, $3

br Label1

High-ILP program executes without stalls

Repeatedly access register file at high rate

Create repeated hot spots at register file

Heat-up time short (1.2ms), cooling time long (12ms)

Degrades CPU utilization to 10%, but

is it due to hogging fetch bandwidth or due to heat?

moderated example of heat stroke
Moderated Example of Heat Stroke

High IPCPhase

Label1:

add $1, $2, $3

br 15*106 Label1

Label2:

ld $4, addr1 (cache miss)

… … …

ld $4, addr9 (cache miss)

br 3*103 Label2

Net ILP low => not hog fetch bandwidth

Register file still accessed at high rate

Cleverly moderated code still inflicts heat stroke

Heat stroke does not monopolize resources

Low IPC Phase

overview11
Overview

Introduction

Heat Stroke Examples

Our Solution to Heat Stroke

Methodology

Results

Conclusions

selective sedation
Selective Sedation

Solution based on two key observations

  • Need stall only culprit thread, notentire pipeline

=> Avoid performance loss for normal threads

  • Access rate of culprit thread higher than others

=> Easy to identify culprit

Two steps in Selective Sedation

  • Correctly and efficiently identify culprit thread
  • Selectively sedate only culprit thread
timely detection of heat stroke
Timely Detection of Heat Stroke

Performance suffers due to long cooling time

Damage already done if hot spot gets created

Use temperature threshold just below emergency [HPCA01]

Detect Heat Stroke in timely manner

Launch Selective Sedation before actual hot spot

identifying culprit thread
Identifying Culprit Thread

Flat average of access rate can be misleading

Need to track recent history

Wt. average counter for recent access-rate history

- Details in paper

When temperature threshold is exceeded

=> Highest value counter indicates culprit thread

selective sedation15
Selective Sedation

Stall fetch of only culprit thread

Remaining threads continue to execute

Allow hot resource to cool

Resume culprit’s fetch when temperature gets normal

  • to avoid starvation of culprit thread

Can report repeat-offender to OS

experimental methodology
Experimental Methodology
  • Extend Wattch to include Hot-Spot and SMT
  • Base case stops pipeline upon a hot spot
  • All simulations run for 500 million cycles
  • Use a history of 0.5 million cycles for identifying culprit
overview17
Overview
  • Introduction
  • Heat Stroke Examples
  • Our Solution to Heat Stroke
  • Methodology
  • Results
  • Conclusions
inflicting and sedating heat stroke
Inflicting and Sedating Heat Stroke

Heat stroke causes repeated hot spots

Selective Sedation drastically contains hot spots

performance impact of heat stroke and selective sedation
Performance Impact of Heat Stroke and Selective Sedation

Our realistic heat sink is reasonable

Heat stroke does not hog resources

Heat stroke causes huge performance loss

Selective Sedation restores performance

effect of sedation on normal programs
Effect of Sedation on Normal programs

Selective Sedation has no adverse effect on normal programs

overview21
Overview

Introduction

Heat-Stroke Examples

Our Solution to Heat Stroke

Methodology

Results

Conclusions

conclusions
Conclusions

Identified Heat Stroke as a novel DOS attack

Proposed Selective Sedation to address Heat Stroke

Identify and stall culprit thread, not entire pipeline

Our results show that selective sedation:

  • Effectively prevents Heat Stroke
  • Is robust across heat-sink and threshold variations
  • Has no adverse effect on normal programs

We identified and solved a novel DOS attack in SMT