1. 2019 2학기 고급운영체제론
ZebRAM: Comprehensive and Compatible Software Protection Against Rowhammer Attacks 3
# 단국대학교 컴퓨터학과 # 남혜민
# 발표자 : 남혜민
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2. Contents 1. Introduction 2. ZebRAM 3. Evaluation 4. QnA
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3. Intro : Word Cloud
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4. Intro : 3-Line Summary
“Introducing ZebRAM, a software-level protection against Rowhammer attacks that leverages the hardware features of DRAM.”
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5. Intro : Rowhammer Attack
DRAM rows consists of DRAM cells
Each cell can store one bit information
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6. Intro : Rowhammer Attack
DRAM rows consists of DRAM cells
Each cell can store one bit information
Rowhammer bug
… and induce bit flips in them: (1 => 0)
or (0 => 1)
Bit flips
Aggressor row
Victim row
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7. Intro : Threat Model 1. Privilege escalation
2. Compromising co-hosted virtual machines
Hypervisor, .etc
3. Attacks over the network
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8. Intro : Simple Threat Ex.
An attacker can flips a bit in:
Cryptographic key, page table entry in kernel etc.
… to compromise the system.
Two important points to note:
Attacker should able to read very fast
Can flip a bit on its neighboring row
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9. Intro : Exploit Paper
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10. Intro : Defenses Paper Rowhammer Existing defenses are ineffective
Even if there is no software bug (and formally verified)
87% of DDR3 DIMMs are vulnerable (Kim et al. ISCA’14)
DDR4 also contain this bug (Van der Veen et al. CCS’17)
Existing defenses are ineffective
Hardware solutions like ECC, TRR are found to ineffective (Cojocar et. al S&P’19, Gruss et al. Blackhat’18)
ANVIL - CPU performance counters to detect Rowhammer attack (AWEKE et. al ASPLOS’16)
CATT - isolates different security domains using guard rows (Brasser et al. SEC’17)
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11. Intro : Defenses Paper Rowhammer Existing defenses are ineffective
Even if there is no software bug (and formally verified)
87% of DDR3 DIMMs are vulnerable (Kim et al. ISCA’14)
DDR4 also contain this bug (Van der Veen et al. CCS’17)
Existing defenses are ineffective
Hardware solutions like ECC, TRR are found to ineffective (Cojocar et. al S&P’19, Gruss et al. Blackhat’18)
ANVIL - fails against DMA-based attacks (Van der Veen et al. CCS’17)
CATT - fails because different security domains share memory (Gruss et al. S&P’18)
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12. ZebRAM
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13. ZebRAM Design : RowHammer Attack Protection
1. Full memory protection
Safe in hardware > FAIL
Software attempts safe > FAIL
2. Limit the rows that an attacker can access
The goal is to design a system where the attacker directly destroys only a subset of the rows.
In other words, to make it impossible to climb
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14. ZebRAM Design : Isolation
1. Separate Security domains using guard rows
2. Isolate security sensitive data using guard rows
User space
Guard Rows
Kernel space
Sensitive data
DRAM address space
CATT uses this approach (Brasser et al. SEC’17)
(Tatar et al. ATC’18)
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15. ZebRAM Design : Basic Odd Row : Data Even Row : Guard
Can stop all Rowhammer
But, waste half of memory
Data row
Guard row
DRAM address space
DRAM address space
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16. ZebRAM Design : Basic With the Buddy page allocation 3 1 2 Data row
Guard row
Data region
(Safe region) 1 2
Guard region
(Unsafe region)
버디 에서 홀수 혹은 짝수를 강제로 사용하지 않게 하려면 이를 위해 물리적 메모리의 연속이 필요하다고 한다.
DRAM address space
DRAM address space
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17. ZebRAM Design 1 2 Data row Data row Guard row Guard row Safe region
Physical address space
Data row
Guard row
Data row
Guard row 1 2
Safe region
Unsafe region
DRAM address space Physical address space
Physical address
space
DRAM address space
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18. ZebRAM Design : Physical to DRAM
Translating physical addresses to DRAM addresses and placing guard rows
Physical address space
Data row
Guard row 1
RAMSES
+ ALIS*
Physical address
space
DRAM address space
DRAM address translation library, RAMSES
Memory allocator, ALIS (Tatar et al. ATC’18)
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19. ZebRAM Design : Re-mapping
Transparently re-map the data rows and guard rows as two contiguous memory region
We use virtualization feature like Intel (VT-x) …
Safe region for OS 2
VT-x
Unsafe region
DRAM address space
DRAM address space
Physical address space
Physical address space
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20. ZebRAM Design : Basic Using unsafe region to overcome memory waste.
Two conditions for using unsafe region
1. Correctly handle potential bit flips in unsafe areas
2. Access to an unsafe area must not cause a bit flip of the safe area.
Data region
(Safe region)
Guard region
(Unsafe region) 3
Physical address space
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21. ZebRAM Design : Basic Securely means two things here :
Handle bit flips that may occur on unsafe region
ZebRAM implements a integrity manager that uses:
Hash verification (SHA-256)
Error correction code (ECC)
Safe region
for OS
Integrity Manager
Unsafe region
Physical address space
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22. ZebRAM Design : Basic Securely means two things:
Handle bit flips that may occur on unsafe region
Protect the unsafe region from illegal bit flips
ZebRAM slows down the consecutive accesses
to the same location in the unsafe region:
By implements a cache layer using safe memory
Enforcing Least-recently-added eviction policy
Safe region f or OS
Cache layer
Unsafe region
Physical address space
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23. ZebRAM Design : Basic Efficiently:
Exposes the unsafe region as swap space to the OS
Helps to utilize efficient page replacement policies
in commodity OS
Safe region f or OS
Integrity Manager
Cache layer
Swap space
Physical address space
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24. ZebRAM Design : Components
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25. ZebRAM Design : Components
1. Memory Remapper
2. Integrity Manager
3. Cache Manager
4. Swap Manager
컨트롤 패킷에 대한 보안 적용 필요
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26. Memory Remapper Split of physical memory into a safe and unsafe region
One region contains all the even-numbered rows
The other contains all the odd-numbered rows.
Data row
Guard row
컨트롤 패킷에 대한 보안 적용 필요
DRAM address space
DRAM address space
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27. Integrity Manager Protects the integrity of the unsafe region
For error correction, usingh a commonly-used Single-Error Correction and Double-Error Detection (SECDED)
ZebRAM provides the possibility to mix SECDED with collision resistant hash functions (SHA-256)
-Hamming code-
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28. Cache Manager Implements a fully associative cache Advantage
Reducing the access frequency on memory rows in the unsafe region.
Speeds up access to the swap space
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29. Swap Manager Uses the unsafe region
Protected by the Integrity Manager and Accessible only by the OS.
Advantage
OS will only access the slow
Integrity-checked unsafe region when it runs out of fast safe memory.
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30. # Life of a page in ZebRAM world
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31. Life of a page in ZebRAM world
Safe region
Swap Space
Cache
Kswapd
Compression/ Decompression
Hash Generation/ Verification
ECC Encoder/ Decoder 21

32. Life of a page in ZebRAM world
Safe region
Swap Space
Cache
Kswapd
Compression/ Decompression
Hash Generation/ Verification
ECC Encoder/ Decoder 21

33. Life of a page in ZebRAM world
Safe region
Swap Space
Cache
Kswapd
Compression/ Decompression
Hash Generation/ Verification
ECC Encoder/ Decoder 21

34. Life of a page in ZebRAM world
Safe region
Swap Space
Cache
Kswapd
Compression/ Decompression
Hash Generation/ Verification
ECC Encoder/ Decoder 21

35. Life of a page in ZebRAM world
Safe region
Swap Space
Cache
Kswapd
Compression/ Decompression
Hash Generation/ Verification
ECC Encoder/ Decoder 21

36. Life of a page in ZebRAM world
Safe region
Swap Space
Cache
Kswapd
Compression/ Decompression
Hash Generation/ Verification
ECC Encoder/ Decoder 21

37. Life of a page in ZebRAM world
Safe region
Swap Space
Cache
Kswapd #
Compression/ Decompression
Hash Generation/ Verification
ECC Encoder/ Decoder 21

38. Life of a page in ZebRAM world
Safe region #
Swap Space
Cache
Kswapd
Compression/ Decompression
Hash Generation/ Verification
ECC Encoder/ Decoder 21

39. Life of a page in ZebRAM world
Safe region #
Swap Space
Cache
Kswapd
Compression/ Decompression
Hash Generation/ Verification
ECC Encoder/ Decoder 21

40. Life of a page in ZebRAM world
Safe region #
Swap Space
Cache
Kswapd
Compression/ Decompression
Hash Generation/ Verification
ECC Encoder/ Decoder 21

41. Life of a page in ZebRAM world
Safe region #
Swap Space
Cache
Kswapd
Compression/ Decompression
Hash Generation/ Verification
ECC Encoder/ Decoder 21

42. Life of a page in ZebRAM world
Safe region #
Swap Space X
Cache
Kswapd
Compression/ Decompression
Hash Generation/ Verification
ECC Encoder/ Decoder 21

43. Life of a page in ZebRAM world
Safe region #
Swap Space
Cache
Kswapd X
Compression/ Decompression
Hash Generation/ Verification
ECC Encoder/ Decoder 21

44. Life of a page in ZebRAM world
Safe region #
Swap Space
Cache
Kswapd
Compression/ Decompression
Hash Generation/ Verification
ECC Encoder/ Decoder 21

45. Life of a page in ZebRAM world
Safe region #
Swap Space
Cache
Kswapd #
Compression/ Decompression
Hash Generation/ Verification
ECC Encoder/ Decoder 21

46. Life of a page in ZebRAM world
Safe region #
Swap Space
Cache
Kswapd
Compression/ Decompression
Hash Generation/ Verification
ECC Encoder/ Decoder 21

47. Life of a page in ZebRAM world
Safe region #
Swap Space
Cache
Kswapd
Compression/ Decompression
Hash Generation/ Verification
ECC Encoder/ Decoder 21

48. Life of a page in ZebRAM world
Safe region #
Swap Space
Cache
Kswapd
Compression/ Decompression
Hash Generation/ Verification
ECC Encoder/ Decoder 21

49. Life of a page in ZebRAM world
Safe region #
Swap Space
Cache
Kswapd
Compression/ Decompression
Hash Generation/ Verification
ECC Encoder/ Decoder 21

50. Implementation LKM # Swap Space Safe region Cache Kswapd
Compression/ Decompression
Hash Generation/ Verification
ECC Encoder/ Decoder 21

51. Evaluation 1. Security Evaluation 2. Performance Evaluation
2006 benchmark, Working Set Size
컨트롤 패킷에 대한 보안 적용 필요
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52. Evaluation : Security
We ran the Rowhammer exploit on the ZebRAM protected OS
Take away:
ECC module alone detected 100% the bit flips
ECC module corrected % of the bit flips =
100%
99.9%
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53. Evaluation : Performance
Spec 2006 benchmark shows
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54. Evaluation : Performance
When active working set is using 70% of the memory:
ZebRAM (Basic) = 30x
ZebRAM (ECC) = 3x
ZebRAM (ECC + SHA-256) = 3.9x
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55. Summary
The ZebRAM is the first solution to provide complete protection against Rowhammer attacks
Performance overhead:
Minimal when the active working set fits in the safe region
Function of the active working set size when it does not fit in the safe region
Code for ZebRAM will be available soon at
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56. Q & A Thanks for your Attention
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