Breaking iOS Code Signing - Reverse Engineering Mac OS X

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When to validate/** CODE SIGNING:* When soft faulting a page, we have to validate the page if:* 1. the page is being mapped in user space* 2. the page hasn't already been found to be "tainted"* 3. the page belongs to a code-signed object* 4. the page has not been validated yet or has been mapped for write.*/#define VM_FAULT_NEED_CS_VALIDATION(pmap, page) \((pmap) != kernel_pmap /*1*/ && \!(page)->cs_tainted /*2*/ && \(page)->object->code_signed /*3*/ && \(!(page)->cs_validated || (page)->wpmapped /*4*/))Friday, October 14, 11
Validating code matches hashvm_page_validate_cs ->vm_page_validate_cs_mapped ->vnode_pager_get_object_cs_blobsvnode_pager_get_object_cs_blobs(...){...validated = cs_validate_page(blobs,offset + object->paging_offset,(const void *)kaddr,&tainted);...page->cs_validated = validated;if (validated) {page->cs_tainted = tainted;}sets whether a page isvalidated and taintedFriday, October 14, 11
Page 3 and 4: AgendaCode signing and iOS security
Page 5 and 6: iOS Security ModelAll code (binarie
Page 7 and 8: Malware preventionSince only signed
Page 9 and 10: Exploit mitigationNo pages are writ
Page 11 and 12: ComparisonIn OS XCan allocate RWX p
Page 13 and 14: Overview of internalsMandatory Acce
Page 15 and 16: iOS MAC policiesOnly 2 policies reg
Page 17 and 18: AMFI hooksAMFI uses the following M
Page 19 and 20: mac_vnode_check_execintmac_vnode_ch
Page 21 and 22: mpo_vnode_check_signatureSets CS_HA
Page 23 and 24: Kernel checksparse_machfile(struct
Page 25 and 26: Actual signature validationintubc_c
Page 27 and 28: Code signing so farWhen binary is l
Page 29: Enforcement codevm_fault_enter{.../
Page 33 and 34: When a page is invalidBack in vm_fa
Page 35 and 36: No new codeWe’ve seen how all exe
Page 37 and 38: Existing regionsvm_map_protect(...)
Page 39 and 40: Dynamic codesigningIn order to util
Page 41 and 42: Speed vs securityThere is a (single
Page 43 and 44: MobileSafari# ldid -e /Applications
Page 45 and 46: Inside mmapintmmap(proc_t p, struct
Page 47 and 48: Even further......if (flags & MAP_J
Page 49 and 50: Now we pass the checkvm_map_enter(.
Page 51 and 52: vm_map_enter (again)if ((flags & VM
Page 53 and 54: 7 PatchesCan be found at https://gi
Page 55 and 56: vm_map_enter (again!)vm_map_enter(.
Page 57 and 58: vm_map_protectvm_map_protect(...){.
Page 59 and 60: vm_map_protectvm_map_protect(...){.
Page 61 and 62: Allow “unvalidated” pagesSet cs
Page 63 and 64: MobileSafari shellcodeunsigned int
Page 65 and 66: Unsigned code, iOS 2void (*f)();uns
Page 67 and 68: Questions?Thanks for coming!Friday,
Page 69 and 70: An iOS 5.0 code signing bugintmmap(
Page 71 and 72: An iOS 5.0 code signing bug#define
Page 73 and 74: Allocating RWX regionsAny process w
Page 75 and 76: Running unsigned codeMalicious App
Page 77 and 78: Copy and fixup dyldint fd = open("f
Page 79 and 80: Patch 2uintptr_t ImageLoaderMachO::
Page 81 and 82:
Patch 2uintptr_t ImageLoaderMachO::
Page 83 and 84:
Patch 3void ImageLoaderMachO::mapSe
Page 85 and 86:
Patch 3void ImageLoaderMachO::mapSe
Page 87 and 88:
Patch 4void ImageLoader::link(const
Page 89 and 90:
Apple review processAn app that did
Page 91 and 92:
InstastockAlso rejected - for illeg
Page 93 and 94:
App Store Review ProcessNot very cl
Page 95:
Questions?Contact me at charlie.mil
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Breaking iOS Code Signing - Reverse Engineering Mac OS X

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