Finding 1-Day Vulnerabilities in Trusted Applications using - PowerPoint PPT Presentation

Finding 1-Day Vulnerabilities in Trusted Applications using Selective Symbolic Execution Marcel Busch , Kalle Dirsch 2020-02-23 Friedrich-Alexander-University Erlangen-Nürnberg, Germany BAR’20

BAR’20 Motivation • How secure are Trusted Execution Environments (TEEs)? • What errors do vendors make? • In 2016 Huawei’s TEE got exploited • CVE-2016-8764 [2] • Type confusion bug in the Secure Storage Trusted Application (TA) • How to facilitate binary-diff-based analyses of 1-days in TAs? ⇒ Filter patches dealing with user input ⇒ Compare constraints introduced by patches a a https://www.youtube.com/watch?v=XjbGTZrg9DA 2/16 2020-02-23 | M. Busch | FAU Erlangen-Nürnberg | Finding 1-Day Vulnerabilities in Trusted Applications

BAR’20 Background • Two “Worlds” • Two OSs Normal World Secure World • Two user spaces Client Applications Trusted Applications • Client Application (CA) logically ... ... interacts with TA TEE Internal Core API • Logical channel is carried out by Rich Dispatcher Operating System (Rich OS) and Rich OS Trusted OS Trusted Operating System (Trusted OS) • GlobalPlatform (GP) specification defines “ libc ” of TAs 3/16 2020-02-23 | M. Busch | FAU Erlangen-Nürnberg | Finding 1-Day Vulnerabilities in Trusted Applications

BAR’20 Challenges and Related Work Challenges • TAs are closed source • No dynamic analysis Normal World Secure World ( i.e., debugging) Client Applications Trusted Applications • No TA modifications ( i.e., instrumentation) ... ... TEE Internal Core API Related Work Dispatcher • PartEmu [1] Rich OS Trusted OS • TEEGris Usermode [4] Our prototype, SimTA , focuses on • GP Internal Core API 4/16 2020-02-23 | M. Busch | FAU Erlangen-Nürnberg | Finding 1-Day Vulnerabilities in Trusted Applications

BAR’20 TA Lifecycle while ( 1 ) { 1 LifecycleData* data = MsgRcv(); 2 3 switch ( data->lifecycle_cmd ) { 4 case OPEN_SESS: 5 • TA_CreateEntryPoint : if (data->init) { 6 Constructor TA_CreateEntryPoint(); 7 } 8 • TA_OpenSessionEntryPoint : TA_OpenSessionEntryPoint(...); 9 Opens client session break ; 10 case INVOKE_CMD: 11 • TA_InvokeCommandEntryPoint : TA_InvokeCommandEntryPoint(...); 12 break ; Invocation of TA commands 13 case CLOSE_SESS: 14 • TA_CloseSessionEntryPoint : TA_CloseSessionEntryPoint(...); 15 if (data->deinit) { 16 Closes client session TA_DestroyEntryPoint(); 17 } • TA_DestroyEntryPoint : 18 break ; 19 Destructor default : 20 break ; 21 } 22 MsgSnd(data); 23 } 24 5/16 2020-02-23 | M. Busch | FAU Erlangen-Nürnberg | Finding 1-Day Vulnerabilities in Trusted Applications

BAR’20 TA Parameters TEE_Result TA_OpenSessionEntryPoint( 1 uint32_t paramTypes, typedef union { 2 1 [inout] TEE_Param params[4], struct { 3 2 [out][ctx] void ** sessionContext unsigned int buffer; 4 3 ); unsigned int size; 5 4 } memref; 6 5 TEE_Result TA_InvokeCommandEntryPoint( struct { 7 6 [ctx] void * sessionContext, unsigned int a; 8 7 uint32_t commandID, unsigned int b; 9 8 uint32_t paramTypes, } value; 10 9 [inout] TEE_Param params[4] } TEE_Param; 11 10 ); 12 6/16 2020-02-23 | M. Busch | FAU Erlangen-Nürnberg | Finding 1-Day Vulnerabilities in Trusted Applications

BAR’20 TA CmdId-Handler TA_InvokeCommandEntryPoint(sessCtx, cmdId, paramTypes, params) { 1 switch ( cmdId ) { 2 case FOPEN: 3 if (paramTypes != FOPEN_PTYPES) 4 goto ptype_error; 5 6 char * path; size_t pathsz; 7 uint32_t flags; 8 TEE_ObjectHandle obj; 9 10 path = params[0]->memref.buffer; 11 pathsz = params[0]->memref.size; 12 flags = params[1]->value.a; 13 14 TEE_OpenPersistentObject(TEE_STORAGE_PRIVATE, path, pathsz, flags, &obj); 15 ... 16 break ; 17 case FREAD: 18 ... 19 } 20 return ; 21 ptype_error: 22 log("bad param types"); 23 return ; 24 } 25 7/16 2020-02-23 | M. Busch | FAU Erlangen-Nürnberg | Finding 1-Day Vulnerabilities in Trusted Applications

BAR’20 TA Address Space 0xffffffff shared mem 0xc8020000 • Address space retrieved via stack 0x011b80000 CVE-2016-8764 exploit heap • globaltask implements GP 0x011b40000 Internal Core API storageTA • globaltask is the only library code rodata • TA does not perform syscalls 0x01040000 data • shared mem contains params globaltask code rodata data 0x0119e000 0x00000000 8/16 2020-02-23 | M. Busch | FAU Erlangen-Nürnberg | Finding 1-Day Vulnerabilities in Trusted Applications

BAR’20 SimTA • Maps memory according to our analysis using angr [3] • Hooks input/output of lifecycle via angr-SimProcedures • Modular implementation of call sequences • Allows for selectively chosen symbolic inputs • Hooks GP Internal Core API via angr-SimProcedures • Specification of functions available from GP • Implements all functions used by storageTA • Can be found on GitHub: https://github.com/teesec/simta 9/16 2020-02-23 | M. Busch | FAU Erlangen-Nürnberg | Finding 1-Day Vulnerabilities in Trusted Applications

BAR’20 Evaluation – Approach • Analysis of Secure Storage TA • VNS-L21C432B130 vs VNS-L21C432B160 • Used Zynamic’s BinDiff to identify patches 1 1 3 2 2 • SimTA provides 4 • filter mode – identifies patches dealing 5 6 6 with user-controlled input 9 9 8 8 7 7 • exec mode – runs both versions with selectively chosen symbolic inputs • Found three 1-days 10/16 2020-02-23 | M. Busch | FAU Erlangen-Nürnberg | Finding 1-Day Vulnerabilities in Trusted Applications

BAR’20 Evaluation – CVE-2016-8764 Re-Discovery 1 TA_InvokeCommandEntryPoint(sessCtx, cmdId, 2 paramTypes, params) { 3 switch ( cmdId ) { 4 case FOPEN: 5 ... • Type confusion 6 break ; 7 case FREAD: 8 // if (paramTypes != FOPEN_PTYPES) 9 // goto ptype_error; 1 enum TEE_ParamType { 10 char *dst = params[0]->buffer; 2 TEE_PARAM_TYPE_NONE = 0x0, 11 int sz = params[0]->size; 3 TEE_PARAM_TYPE_VALUE_INPUT = 0x1, 12 ... 4 TEE_PARAM_TYPE_VALUE_OUTPUT = 0x2, 13 TEE_ReadObjectData(obj, dst, sz); 5 TEE_PARAM_TYPE_VALUE_INOUT = 0x3, 14 break ; 6 TEE_PARAM_TYPE_MEMREF_INPUT = 0x5, 15 ... 7 TEE_PARAM_TYPE_MEMREF_OUTPUT = 0x6, 16 ... 8 TEE_PARAM_TYPE_MEMREF_INOUT = 0x7, 17 } 9 }; 18 return ; 19 ptype_error: 20 log("bad param types"); 21 return ; 22 } 11/16 2020-02-23 | M. Busch | FAU Erlangen-Nürnberg | Finding 1-Day Vulnerabilities in Trusted Applications

BAR’20 Evaluation – Heap-based buffer overflow 1 TA_InvokeCommandEntryPoint(sessCtx, cmdId, 2 paramTypes, params) { 3 switch ( cmdId ) { 4 case FOPEN: 5 ... 6 char * path; 7 param0_buf = params[0]->memref.buffer; 8 param0_sz = params[0]->memref.size; 9 10 // if(strlen(param0_buf) != param0_sz) • Missing length check 11 // return -1 12 • Passing attacker provided buffer length 13 path = malloc(strlen(param0_buf)); 14 to MemMove operation 15 ... 16 17 MemMove(path, param0_buf, param0_sz); ... 18 break ; 19 case FREAD: 20 ... 21 ... 22 23 } 24 return ; 25 } 12/16 2020-02-23 | M. Busch | FAU Erlangen-Nürnberg | Finding 1-Day Vulnerabilities in Trusted Applications

BAR’20 Future Work and Limitations • Support more Trusted Core (TC) TAs 1 1 • Larger analysis covering different 3 2 2 versions and more TC TAs 4 5 6 6 • Investigate compatibility with other 8 9 8 9 7 7 TEEs 13/16 2020-02-23 | M. Busch | FAU Erlangen-Nürnberg | Finding 1-Day Vulnerabilities in Trusted Applications

BAR’20 THE END Questions? 14/16 2020-02-23 | M. Busch | FAU Erlangen-Nürnberg | Finding 1-Day Vulnerabilities in Trusted Applications

BAR’20 References Lee Harrison, Hayawardh Vijayakumar, Rohan Padhye, Koushik Sen, and Michael Grace. Partemu: Enabling dynamic analysis of real-world trustzone software using emulation. In Proceedings of the 29th USENIX Security Symposium (USENIX Security 2020) (To Appear) , August 2020. NIST. Cve-2016-8764. https://nvd.nist.gov/vuln/detail/CVE-2016-8764 , 2017. Accessed: 2019-08-28. 15 (1) /16 2020-02-23 | M. Busch | FAU Erlangen-Nürnberg | Finding 1-Day Vulnerabilities in Trusted Applications

BAR’20 Yan Shoshitaishvili, Ruoyu Wang, Christopher Salls, Nick Stephens, Mario Polino, Audrey Dutcher, John Grosen, Siji Feng, Christophe Hauser, Christopher Kruegel, and Giovanni Vigna. SoK: (State of) The Art of War: Offensive Techniques in Binary Analysis. In IEEE Symposium on Security and Privacy , 2016. Alexander Tarasikov. Qemu teegris usermode. https://github.com/astarasikov/qemu/tree/teegris_usermode , 2019. Accessed: 2019-11-30. 16 (2) /16 2020-02-23 | M. Busch | FAU Erlangen-Nürnberg | Finding 1-Day Vulnerabilities in Trusted Applications