Controlled- Channel Attacks: Deterministic Side Channels for Untrusted Operating Systems

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1 Controlled- Channel Attacks: Deterministic Side Channels for Untrusted Operating Systems Yuanzhong Xu, Weidong Cui, Marcus Peinado The University of Texas at Austin, Microsoft Research San Jose, CA May 19, 2015

2 Applications run on top of OS OS 2

3 Reasons to distrust the OS rootkit OS Large code bases, security bugs 3

4 Reasons to distrust the OS Hosted on untrusted cloud OS 4

5 Shielding systems: remove OS from trusted computing base (TCB) Use hypervisor or secure hardware to confine OS Hypervisor- based Overshadow [ASPLOS '08] InkTag [ASPLOS '13] Intel SGX- based Haven [OSDI '14] OS Hypervisor or SGX CPU 5

6 Shielding systems: remove OS from trusted computing base (TCB) Hypervisor or SGX protects application memory pages from OS Secrecy Integrity Protected app memory pages OS Hypervisor or SGX CPU 6

7 Shielding systems: backward- compatibility & functionality Run legacy applications, on a legacy OS (with small or no modifications) OS is still needed Memory management Storage Network OS Efficient memory management Hypervisor or SGX CPU 7

8 Shielding systems: backward- compatibility & functionality Run legacy applications, on a legacy OS (with small or no modifications) Protected app memory pages OS is still needed Memory management Storage Network OS Integrity Application page table Hypervisor or SGX CPU 8

9 9

10 Breaking the shield (1/3) JPEG decoding (libjpeg) OS Hypervisor (InkTag) or SGX CPU (Haven) 10

11 Breaking the shield (2/3) Font rendering (FreeType) 100% accuracy English letters Common punctuation marks The treasure is buried ten feet north of the third palm tree OS The treasure is buried ten feet north of the third palm tree Hypervisor (InkTag) or SGX CPU (Haven) 11

12 Breaking the shield (3/3) Spell checking (Hunspell) 96% accuracy All words in novel The Wizard of OZ Folklore, legends, myths and fairy tales OS folklore *legend* myths and fairy *tale* Hypervisor (InkTag) or SGX CPU (Haven) 12

13 How? Controlled- channel attacks Side channel attacks from the OS Powerful due to the OS control over the applications Side channel 13

14 Side- channel attacks Traditional side channels: cache access, power consumption, network traffic Victim secret

15 Side- channel attacks Traditional side channels: cache access, power consumption, network traffic System noise: context switches, TLB flushes, exceptions, page faults Victim secret 15

16 Side channels for the OS Under attacker s control System noise: context switches, TLB flushes, exceptions, page faults Victim secret Noise- free channel OS 16

17 Controlled- channel attacks Page faults as a side channel Deterministic: OS controls page tables Set traps by making pages inaccessible Do not need timing Challenge: page- level granularity Protected app memory pages OS Hypervisor or SGX CPU Page faults Application page table 17

18 Input- dependent memory access Page X input if (input) Page Y Page Z Page fault sequence X, Y func1() func2() Page fault sequence X, Z 18

19 Input- dependent memory access Page X input = n N <= 3 Page fault sequence: X, Y Page Y array read array[n] Page Z N >= 4 Page fault sequence: X, Z 19

20 Hunspell Open- source spell checker, used in 20

21 Hunspell hash table Separate chaining Pointer array: index is hash code PG 1 PG 2 PG 3 PG 4 Load Assumption: Dictionary is known Linked lists a attack change channel side size PG 5 PG 6 PG 7 Page faults Page- level knowledge about layout 21

22 Hunspell hash table lookup Input: side channel attack PG 1 PG 2 PG 3 PG 4 while (word) { n = hash(word); listnode = table[n]; while (listnode) { if (equal(listnode, word)) break; listnode = listnode- >next; } a attack change channel side size PG 5 PG 6 PG 7 } if (listnode) success(); else failure(); word = get_next(); 22

23 Hunspell hash table lookup Input: side channel attack PG 1 PG 2 PG 3 PG 4 while (word) { n = hash(word); listnode = table[n]; } while (listnode) { if (equal(listnode, word)) break; listnode = listnode- >next; } if (listnode) success(); else failure(); word = get_next(); a attack change channel side size PG 5 PG 6 PG 7 Page faults: 4 23

24 Hunspell hash table lookup Input: side channel attack PG 1 PG 2 PG 3 PG 4 while (word) { n = hash(word); listnode = table[n]; } while (listnode) { if (equal(listnode, word)) break; listnode = listnode- >next; } if (listnode) success(); else failure(); word = get_next(); a attack change channel side size PG 5 PG 6 PG 7 Page faults:

25 Hunspell hash table lookup Input: side channel attack PG 1 PG 2 PG 3 PG 4 while (word) { n = hash(word); listnode = table[n]; } while (listnode) { if (equal(listnode, word)) break; listnode = listnode- >next; } if (listnode) success(); else failure(); word = get_next(); a attack change channel side size PG 5 PG 6 PG 7 Page faults:

26 Hunspell hash table lookup Input: side channel attack PG 1 PG 2 PG 3 PG 4 while (word) { n = hash(word); listnode = table[n]; } while (listnode) { if (equal(listnode, word)) break; listnode = listnode- >next; } if (listnode) success(); else failure(); word = get_next(); a attack change channel side size PG 5 PG 6 PG 7 Page faults:

27 Hunspell hash table lookup Input: side channel attack PG 1 PG 2 PG 3 PG 4 while (word) { n = hash(word); listnode = table[n]; } while (listnode) { if (equal(listnode, word)) break; listnode = listnode- >next; } if (listnode) success(); else failure(); word = get_next(); a attack change channel side size PG 5 PG 6 PG 7 Page faults:

28 Hunspell hash table lookup Input: side channel attack PG 1 PG 2 PG 3 PG 4 while (word) { n = hash(word); listnode = table[n]; } while (listnode) { if (equal(listnode, word)) break; listnode = listnode- >next; } if (listnode) success(); else failure(); word = get_next(); a attack change channel side size PG 5 PG 6 PG 7 Page faults:

29 Hunspell hash table lookup Input: side channel attack PG 1 PG 2 PG 3 PG 4 while (word) { n = hash(word); listnode = table[n]; } while (listnode) { if (equal(listnode, word)) break; listnode = listnode- >next; } if (listnode) success(); else failure(); word = get_next(); a attack change channel side size PG 5 PG 6 PG 7 Page faults:

30 Hunspell hash table lookup Input: side channel attack PG 1 PG 2 PG 3 PG 4 while (word) { n = hash(word); listnode = table[n]; } while (listnode) { if (equal(listnode, word)) break; listnode = listnode- >next; } if (listnode) success(); else failure(); word = get_next(); h a attack change channel side size PG 5 PG 6 PG 7 Page faults: 4 7 h h3 5 side channel attack 30

31 Hunspell hash table lookup PG 1 PG 2 PG 3 PG 4 Hash function shuffles the order Low correlation between The address of the head pointer The addresses of the list nodes Low ambiguity a attack hash change channel side size PG 5 PG 6 PG 7 h Page faults: 4 7 h h3 5 side channel attack 31

32 Attack results Implemented 3 attacks (Hunspell, FreeType, libjpeg) on both Haven and InkTag Hunspell (spell checking) ~96% accuracy for novel The Wizard of Oz FreeType(font rendering) 100% accuracy for any English input (letters and punctuation marks) 32

33 libjpeg results 33

34 Performance overhead Non- trivial overhead due to expensive page fault handling The attacks are still realistic to execute Hunspell: 2.94s to check the entire novel (39,719 words) FreeType: 0.52s to render 5 KB text Small run time may be hidden in noises 34

35 Thoughts on potential mitigations Ø No great off- the- shelf solution Applications: rewrite to hide access patterns Manually (e.g., OpenSSL) or by compiler High cost for complex legacy apps: engineering effort & performance overhead Shielding systems:more restrictions over the OS Restrictions on memory management May affect functionality Rethink the challenges for Overshadow s vision protect legacy applications from legacy untrusted operating systems 35

36 Conclusion An untrusted OS can construct noise- free side channels. The page- fault side channel leaks large amounts of information about legacy applications. Controlled- channel attacks must be addressed in the design of shielding systems. 36

Controlled-Channel Attacks: Deterministic Side Channels for Untrusted Operating Systems. Yuanzhong Xu, Weidong Cui, Marcus Peinado

Controlled-Channel Attacks: Deterministic Side Channels for Untrusted Operating Systems. Yuanzhong Xu, Weidong Cui, Marcus Peinado : Deterministic Side Channels for Untrusted Operating Systems Yuanzhong Xu, Weidong Cui, Marcus Peinado 2 Goal Protect the data of applications running on remote hardware 3 New tech Trusted Platform Modules