ScaRR

ScaRR: Scalable Runtime
Remote Attestation for
Complex Systems
Flavio Toffalini - Singapore University of Technology and Design
Eleonora Losiouk, Andrea Biondo - University of Padua
Jianying Zhou - Singapore University of Technology and Design
Mauro Conti - University of Padua
RAID - September 23-25, 2019 - Beijing, China

Problem: Remote Attestation
Veriﬁer (trust) Prover (not-so-trust)
Challenge
Report
Application
Is this ok?
2/27Toﬀalini et al., (2019) ScaRR: Scalable Runtime Remote Attestation for Complex Systems

What we can verify: Static properties
- Software loaded
- Hardware integrity
What we can’t verify: Dynamic properties
- Execution path
- Data correctness
ScaRR
3/27
Static Remote Attestation
Toﬀalini et al., (2019) ScaRR: Scalable Runtime Remote Attestation for Complex Systems

Veriﬁer Prover
Report
(hash_ep, output)
ApplicationValid
Execution
Paths
analyze(Application)
Ofﬂine Analysis Online Analysis
4/27
Runtime Remote Attestation
Challenge
(nonce, input)

Limitations
1. Ofﬂine analysis does not scale for big applications
2. Based on heuristics
3. Symbolic execution too slow for the veriﬁcation
5/27
Previous Runtime Remote Attestation

V P
V
More complex applications
More advanced systems
No-physical attacks
6/27
Scenario: Virtual Machines in a Cloud
intra-cloud
communication
ext-cloud
com
m
unication

N1
N2
N3
N5
N4
N6
a
N1
N2
N3
N4
N5
N6
x = input()
if x == ‘auth’:
y = get_privileged_info()
else:
y = get_unprivileged_info()
output(y)
terminate
= return address corruption
7/27
Basic Example

Attacks:
- Standard code-reuse attack (e.g., ROP, JOP)
- Code injection (e.g., shellcode)
- Function hooks
- Attacker takes control of user-space
Prover Assumptions:
- Prover is equipped with a trusted anchor
- Standard defences like W⊕X
- CFI != The attack could come anywhere from within the machine
8/27
Assumptions and Attacker Model

N1
−N4
=> [ (N2
,N4
) ]
N1
−N3
=> [ (N2
,N3
) ]
N3
−N6
=> [ ]
N4
−N6
=> [ ]
NOTE: ScaRR does not consider (N4
,N5
) and (N3
,N5
)
N1
N2
N3
N5
N4
N6
Checkpoint
(e.g., beginning
thread, syscall,
API call)
List of
Actions
Edge
9/27
Idea of ScaRR

- Loop
- Recursion
- Signal
- Exception
10/27
Model Challenges

SA
−N1
=> [ ]
N1
−N1
=> [ (N1
,N2
) ]
N1
−SB
=> [ (N1
,N3
) ]
SA
N1
SB
N2
N3
virtual -checkpoint
11/27
Loop

PB
virtual -checkpoint
a()
N3
N1
N2
PE
call ret
call
ret
PB
−N2
=> [ (PB
,N1
), (N1
,N2
) ]
N2
−N2
=> [ (N2
,N1
), (N1
,N2
) ]
N2
−N2
=> [ (N2
,N1
), (N1
,N3
), (N3
,N2
) ]
N2
−PE
=> [ (N2
,N1
), (N1
,N3
), (N3
,PE
) ]
PB
−PE
=> [ (PB
,N1
), (N1
,N3
), (N3
,PE
) ]
12/27
Recursion

SA
EA
EB
N1
SB
N2
Catch Block
or
Signal Handler
Thread
1. Pause thread LoA
2. Trace new LoA for catch block
signal handler
3. Resume thread LoA
13/27
Signal and Exception

14/27
ScaRR Design
Verifier ProverChallenge
(nonce, input)
ApplicationOffline
Measurements**
analyze(Application)
Offline Analysis Online Analysis
*list of reports and output go in parallel
**LoA + extra info
(output)
List of Reports*
(Cb, Cr, H(LoA))

Ofﬂine Measurements
(Veriﬁer side)
Partial Report (Online Measurements)
(Prover side)
(Cb, Ce, H(LoA))(Cb,Ce,H(LoA)) => [ (M1
,A1
) ... ]
Hash of LoA
Beginning
checkpoint
End
checkpoint
List of Action
15/27
Measurements

(Cb, Ce, H(LoA))
Hash of LoA
Beginning
checkpoint
End
checkpoint
H(LoA) is in
DB?
Cet-1
== Cbt
ss(H(LoA))
(Check1)
(Check2)
(Check3)
OK!
abort()
abort()
abort()
n
y
y
y
n
n
/* shadow stack */
Partial Report
16/27
Veriﬁcation

S
M1
M2
M3
M4
E
A1
C
A2
int main(int argc, char ** argv) {
a(10);
/* irrelevant code */
a(6);
return 0;
}
void a(int x) {
/* irrelevant code */
printf("%dn", x);
return;
}
(S,C,H1
) => [ (M1
,A1
) ]
(C,C,H2
) => [ (A2
,M2
), (M3
,A1
) ]
(C,E,H3
) => [ (A2
,M4
) ]
Ofﬂine measurement, a map between
valid Partial Report and LoA
17/27
Remote Shadow Stack

(M1
,A1
)
(M1
,A1
)
(A2
,M2
) (M3
,A1
)
(M3
,A1
)
(A2
,M2
)
valid!
(A2
,M2
) ret_to (M1
,A1
)
not valid!
(A2
,M2
) ret_to (M3
,A1
)
(S,C,H1
) (C,C,H2
) (C,C,H2
)
Time
Offline measurement:
(S,C,H1
) => [ (M1
,A1
) ]
(C,C,H2
) => [ (A2
,M2
), (M3
,A1
) ]
(C,E,H3
) => [ (A2
,M4
) ]
Attack:
(S,C,H1
)→(C,C,H2
)→(C,C,H2
)→
(Check1) and
(Check2) hold!
18/27
Remote Shadow Stack

Implementation
- Ofﬂine Analysis
- Prover

C/C++ program LLVM/Clang
Instrumented
Application
CRAB
Offline
Measurement
// abstract
// interpretation
20/27
Oﬄine Analysis

User-Space
Application Process // instrumented
Kernel-Space
ScaRR Libraries // to communicate with the kernel
ScaRR sys_measureScaRR ModuleScaRR sys_addaction// custom kernel
// as trusted anchor
// 2 new syscalls
21/27
Prover

Evaluation
Based on SPEC-CPU 2017
- Attestation Speed
- Veriﬁcation Speed
- Network Impact
- Security Properties

Previous works
20K/30K cf-events
23/27
Attestation Speed

From 1.4 M/s to 2.7 M/s
Previous work from 110 to 30k cf-events/s
(Check1) => constant hashmap fetching
(Check2) => constant operation
(Check3) => O(#actions for LoA)
Average LoA size
24/27
Veriﬁcation Speed

Problem:
Too many reports -> network
overload
Solution:
Compress groups of reports
25/27
Network Impact

Security Properties
✓ Code Injection: jumping to shellcode produces wrong LoA
✓ Code-reuse Attacks: produces wrong LoA
✓ Overwrite Nodes: invalid static attestation

Technical Limitation
- Context switch still too slow (considered PT too)
- Be kernel-agnostic by using other trusted anchor
(e.g., SGX, TrustZone)
- Require source code
- CFG generation affects precisions of attack detections

Thank you for attention…
Flavio Toffalini - flavio_toffalini@mymail.sutd.edu.sg
28

ScaRR

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