Adding ASLR to Jailbroken iPhones [PDF] - Antid0te

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Analysing the small values • reason for differences in small values was not discovered until dyld_shared_cache was relocated and applications did not work • objc applications could not find selectors • problem was finally found with reverse engineering • lower 2 bits of size field used as a flag • method list sorted by selectors => allows faster lookup typedef struct method_t { SEL name; const char *types; IMP imp; } method_t; typedef struct method_list_t { uint32_t entsize_NEVER_USE; // low 2 bits used for fixup markers uint32_t count; struct method_t first; } method_list_t; Stefan Esser • Adding ASLR to jailbroken iPhones • December 2010 • 38
What needs to be rebased? • images must be shifted around • image pointers in dyld_shared_cache header • Mach-O-Headers • segment addresses / segment file offsets • section addresses / section file offsets • LC_ROUTINES • symbols • export trie • section content accoring to collected differences • __objc_opt_ro selector table in libobjc.dylib Stefan Esser • Adding ASLR to jailbroken iPhones • December 2010 • 39
Page 1 and 2: http://www.sektioneins.de Adding AS
Page 3 and 4: What the talk is NOT about This tal
Page 5 and 6: Part I Introduction Stefan Esser
Page 7 and 8: Jailbroken iPhones and Security •
Page 9 and 10: Codesigning ??? • every binary on
Page 11 and 12: Example Crashdump CrashReporter Key
Page 13 and 14: Part II Dyld Shared Cache and ASLR
Page 15 and 16: Libraries where are thou? • since
Page 17 and 18: dyld_shared_cache Header Stefan Ess
Page 19 and 20: Rebasing the Libraries... • okay
Page 21 and 22: the iPhone SDK to the rescue? (II)
Page 23 and 24: Okay what now ? looking at differen
Page 25 and 26: Obvious Complications • different
Page 27 and 28: Let‘s start diffing • Python im
Page 29 and 30: Analysing the results (I) • Expec
Page 31 and 32: What are the two large unknown valu
Page 33 and 34: Small Values and Pointers • some
Page 35 and 36: iPhone libobjc does not match the s
Page 37: Analysing the different pointer pro
Page 41 and 42: The Dynamic Linker • iPhone OS /
Page 43 and 44: Relocating the Dynamic Linker (II)
Page 45 and 46: Stack Randomization (I) • stack o
Page 47 and 48: Stack Randomization Test int main()
Page 49 and 50: Baby Steps... • generic solution
Page 51 and 52: Crazy Solution • Crazy Solution
Page 53 and 54: Brute Force Pointer Detection (II)
Page 55 and 56: Part IV Installing it on the iPhone
Page 57 and 58: Analysis of current Jailbreak • /
Page 59 and 60: Installing an alternative dyld •
Page 61 and 62: Thank you for listening... DEMO Ste

Adding ASLR to Jailbroken iPhones [PDF] - Antid0te

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