Micro-architectural Attacks 1
1
Milan Patnaik
IIT Madras
Things we thought
gave us security!
• Cryptography
• Passwords
• Information Flow Policies
• Privileged Rings
• ASLR
• Virtual Machines and confinement
• Javascript and HTML5
(due to restricted access to system
resouces)
• Enclaves (SGX and Trustzone)
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Micro-Architectural Attacks
(can break all of this)
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Cache timing attackCache timing attack
Branch prediction attackBranch prediction attack
Speculation AttacksSpeculation Attacks
Row hammerRow hammer
Fault Injection AttacksFault Injection Attacks
….. and many more….. and many more
cold boot attackscold boot attacks
• Cryptography
• Passwords
• Information Flow Policies
• Privileged Rings
• ASLR
• Virtual Machines and confinement
• Javascript and HTML5
(due to restricted access to system
resouces)
• Enclaves (SGX and Trustzone)
DRAM Row buffer (DRAMA)DRAM Row buffer (DRAMA)
Causes
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performance
security
Most micro-architectural attacks caused by
performance optimizations
Others due to inherent device properties
Third, due to stronger attackers
Cache Timing Attacks
Cache Covert Channels
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Cache Timing Attacks
Flush + Reload Attack
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Copy on Write
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if (fork() > 0){
// in parent process
} else{
// in child process
}
2
• Making a copy of a process
is called forking.
– Parent (is the original)
– child (is the new process)
• When fork is invoked,
– child is an exact copy of
parent
• When fork is called all pages
are shared between parent
and child
• Easily done by copying the
parent s page tables
Physical Memory
Parent
Page
Table
Child
Page
Table
Virtual Addressing Advantage
(easy to make copies of a process)
Child created is an exact replica of the parent process.
- Page tables of the parent duplicated in the child
- New pages created only when parent (or child) modifies data
- Postpone copying of pages as much as possible, thus
optimizing performance
- Thus, common code sections (like libraries) would be
shared across processes.
Process Tree
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:
SSLEncryption()
:
init
:
SSLEncryption()
:
Physical Memory
Virtual Memory
(process 1)
Virtual Memory
(process 2)
Interaction with the LLC
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ProcessesProcesses
Core 1Core 1
LLCLLC
:
SSLEncryption()
:
cache misses slow
Core 2Core 2
ProcessesProcesses
Interaction with the LLC
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:
SSLEncryption()
:
cache hits
:
SSLEncryption()
:
fast
One process can affect the
execution time of another process
ProcessesProcesses
Core 1Core 1
LLCLLC
Core 2Core 2
ProcessesProcesses
Flush + Reload Attack on LLC
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Part of an encryption algorithm
executed only when ei = 1
clflush Instruction
Takes an address as input.
Flushes that address from all caches
clflush (line 8)
Flush+Reload Attack, Yuval Yarom and Katrina Falkner (https://eprint.iacr.org/2013/448.pdf)
Flush + Reload Attack
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:
SSLEncryption()
:
:
Clflush(line 8)
:
flush
reload
access victim
attacker
ProcessesProcesses
Core 1Core 1
LLCLLC
Core 2Core 2
ProcessesProcesses
Flush+Reload Attack
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Countermeasures
• Do not use copy-on-write
– Implemented by cloud providers
• Permission checks for clflush
– Do we need clflush?
• Non-inclusive cache memories
– AMD
– Intel i9 versions
• Fuzzing Clocks
• Software Diversification
– Permute location of objects in memory (statically and dynamically)
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Cache Collision Attacks
Prime + Probe Attack
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Prime + Probe Attack
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Core 1Core 1
Last Level CacheLast Level Cache
Core 2Core 2
VictimVictim
SMT
Core
SMT
Core
L1 Cache MemoryL1 Cache Memory
SpySpy
VictimVictim SpySpy
way 0 way 1 way 2 way 3
Set 0
Set 1
Set 2
Set 3
Set N-2
Set N-1
Prime Phase
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way 0 way 1 way 2 way 3
Set 0
Set 1
Set 2
Set 3
While(1){
for(each cache set){
start = time();
access all cache ways
end = time();
access_time = end – start
}
wait for some time
}
Victim Execution
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way 0 way 1 way 2 way 3
Set 0
Set 1
Set 2
Set 3
The execution causes some of
the spy data to get evicted
Probe Phase
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way 0 way 1 way 2 way 3
Set 0
Set 1
Set 2
Set 3
While(1){
for(each cache set){
start = time();
access all cache ways
end = time();
access_time = end – start
}
wait for some time
}
Time taken by sets that have
victim data is more due to the cache
misses
Probe Time Plot
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0 63
Each row is an iteration of the while loop; darker shades imply higher memory access time
Prime + Probe in Cryptography
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char Lookup[] = {x, x, x, . . . x};
char RecvDecrypt(socket){
char key = 0x12;
char pt, ct;
read(socket, &ct, 1);
pt = Lookup[key ^ ct];
return pt;
}
The attacker know the address of Lookup and the ciphertext (ct)
The memory accessed in Lookup depends on the value of key
Given the set number, one can identify bits of key ^ ct.
Key dependent memory accesses
Keystroke Sniffing
• Keystroke  interrupt  kernel mode switch  ISR execution  add to keyboard
buffer  …  return from interrupt
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way 0 way 1 way 2 way 3
Set 0
Set 1
Set 2
Set 3
Keystroke Sniffing
• Regular disturbance seen in Probe Time Plot
• Period between disturbance used to predict passwords
34
Svetlana Pinet, Johannes C. Ziegler, and F.-Xavier Alario. 2016. Typing Is Writing: Linguistic Properties Modulate
Typing Execution. Psychon Bull Rev 23, 6
Web Browser Attacks
• Prime+Probe in
– Javascript
– pNACL
– Web assembly
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Extract Gmail secret key
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https://www.cs.tau.ac.il/~tromer/drivebycache/drivebycache.pdf
Website Fingerprinting
• Privacy: Find out what websites are being
browsed.
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Cross VM Attacks (Cache)
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Cross VM Attacks (DRAM)
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Cache Collision Attacks
Time Driven Attacks
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Internal Collision Attacks
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(Adversary)
Victim
Internal Collisions on a Cipher
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Table Table
Part of a Cipher
P0 ,P4
(Adversary)
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If cache hit (less time) : If cache miss (more time):
00 KP  44 KP 
4P0P
0K 4K
4040
4400
PPKK
KPKP


4040
4400
PPKK
KPKP


T
P0
K0
T
P4
K4
Block Cipher
Random
P0
Cipher Text
P4
Suppose
(K0 = 00 and k4 = 50)
• P0 = 0, all other inputs are
random
• Make N time measurements
• Segregate into Y buckets
based on value of P4
• Find average time of each
bucket
• Find deviation of each
average from overall
average (DOM)
P4 Average
Time
DOM
00 2945.3 1.8
10 2944.4 0.9
20 2943.7 0.2
30 2943.7 0.2
40 2944.8 1.3
50 2937.4 -6.3
60 2943.3 -0.2
70 2945.8 2.3
: : :
F0 2941.8 -1.7
Average : 2943.57
Maximum : -6.34040
PPKK 
That’s for the Day !!
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