add method 1 hooking for x86_64; method 3 first commit

macho-go/internal/wrapper/info.go

@@ -46,6 +46,8 @@ func (printer *InfoPrinter) Print() {
 			)
 		}
 
+    mc.CollectObjectiveCClasses()
+
 		fmt.Println("======")
 	}
 }

macho-go/pkg/ios/macho/objc.go

@@ -6,10 +6,164 @@ import (
 	"fmt"
 	"io"
 	"strings"
+  "unsafe"
 
 	. "ios-wrapper/pkg/ios"
 )
 
+// #include "fixups.h"
+import "C"
+
+func (mc *MachoContext) CollectObjectiveCClasses() {
+  var objc_const *bytes.Reader
+  var objc_const_start uint64
+  var objc_const_end uint64
+  // var objc_methname []byte
+
+	for _, cmd := range mc.commands {
+		if cmd.Cmd() == LC_MAIN {
+			continue
+		}
+		if cmd.Cmd() != LC_SEGMENT_64 {
+			continue
+		}
+		var segment = cmd.(*Segment64)
+
+    // we assume the binary comes in perfect ordering, that is as laid out below
+
+		if bytes.Compare(bytes.Trim(segment.SegName(), "\x00"), []byte("__TEXT")) == 0 {
+			for _, section := range segment.Sections() {
+        buffer := make([]byte, section.Size())
+        mc.file.ReadAt(buffer, int64(section.Offset()))
+				if bytes.Compare(bytes.Trim(section.SectName(), "\x00"), []byte("__objc_stubs")) == 0 {
+				}
+				if bytes.Compare(bytes.Trim(section.SectName(), "\x00"), []byte("__objc_methlist")) == 0 {
+				}
+				if bytes.Compare(bytes.Trim(section.SectName(), "\x00"), []byte("__objc_methname")) == 0 {
+          // objc_methname := buffer
+				}
+				if bytes.Compare(bytes.Trim(section.SectName(), "\x00"), []byte("__objc_classname")) == 0 {
+				}
+				if bytes.Compare(bytes.Trim(section.SectName(), "\x00"), []byte("__objc_methtype")) == 0 {
+				}
+			}
+		}
+		if bytes.Compare(bytes.Trim(segment.SegName(), "\x00"), []byte("__DATA_CONST")) == 0 {
+			for _, section := range segment.Sections() {
+        buffer := make([]byte, section.Size())
+        mc.file.ReadAt(buffer, int64(section.Offset()))
+				if bytes.Compare(bytes.Trim(section.SectName(), "\x00"), []byte("__objc_classlist")) == 0 {
+				}
+				if bytes.Compare(bytes.Trim(section.SectName(), "\x00"), []byte("__objc_nlclslist")) == 0 {
+				}
+				if bytes.Compare(bytes.Trim(section.SectName(), "\x00"), []byte("__objc_imageinfo")) == 0 {
+				}
+			}
+    }
+		if bytes.Compare(bytes.Trim(segment.SegName(), "\x00"), []byte("__DATA")) == 0 {
+			for _, section := range segment.Sections() {
+        buffer := make([]byte, section.Size())
+        mc.file.ReadAt(buffer, int64(section.Offset()))
+        reader := bytes.NewReader(buffer)
+				if bytes.Compare(bytes.Trim(section.SectName(), "\x00"), []byte("__objc_const")) == 0 {
+          objc_const = reader
+          objc_const_start = uint64(section.Offset())
+          objc_const_end = objc_const_start + section.Size()
+				}
+				if bytes.Compare(bytes.Trim(section.SectName(), "\x00"), []byte("__objc_selrefs")) == 0 {
+				}
+				if bytes.Compare(bytes.Trim(section.SectName(), "\x00"), []byte("__objc_classrefs")) == 0 {
+				}
+				if bytes.Compare(bytes.Trim(section.SectName(), "\x00"), []byte("__objc_superrefs")) == 0 {
+				}
+				if bytes.Compare(bytes.Trim(section.SectName(), "\x00"), []byte("__objc_data")) == 0 {
+          // this section contains a series of class_t
+          // struct _class_t {
+          //   struct _class_t *isa;
+          //   struct _class_t * const superclass;
+          //   void *cache;
+          //   IMP *vtable;
+          //   struct class_ro_t *ro;
+          // };
+
+          for i := uint64(0); i < (section.Size() / uint64(mc.pointersize * 5)); i++ {
+            var isa uint64
+            var superclass uint64
+            var cache uint64
+            var vtable uint64
+            var ro uint64
+            binary.Read(reader, mc.byteorder, &isa)
+            binary.Read(reader, mc.byteorder, &superclass)
+            binary.Read(reader, mc.byteorder, &cache)
+            binary.Read(reader, mc.byteorder, &vtable)
+            binary.Read(reader, mc.byteorder, &ro)
+
+
+            fmt.Printf("at=0x%x\n", section.Offset() + uint32(i) * mc.pointersize * 5)
+            fmt.Printf("isa=0x%x superclass=0x%x\n", isa, superclass)
+            fmt.Printf("cache=0x%x vtable=0x%x\n", cache, vtable)
+            fmt.Printf("ro=0x%x\n", ro)
+
+            var bind int
+            var ret1 uint64
+            var ret2 uint64
+            C.ParseFixValue(C.int(2), C.uint64_t(ro),
+              (*C.int)(unsafe.Pointer(&bind)),
+              (*C.uint64_t)(unsafe.Pointer(&ret1)),
+              (*C.uint64_t)(unsafe.Pointer(&ret2)),
+            )
+
+            // is rebase, because ro points to objc_const
+            // and address is in range
+            if (bind != 1 && ret1 >= objc_const_start && ret1 < objc_const_end) {
+              offset := ret1 - objc_const_start
+              objc_const.Seek(int64(offset), 0)
+
+              // struct _class_ro_t {
+              //   uint32_t const flags;
+              //   uint32_t const instanceStart;
+              //   uint32_t const instanceSize;
+              //   uint32_t const reserved;  // only when building for 64bit targets
+              //   const uint8_t * const ivarLayout;
+              //   const char *const name;
+              //   const struct _method_list_t * const baseMethods;
+              //   const struct _protocol_list_t *const baseProtocols;
+              //   const struct _ivar_list_t *const ivars;
+              //   const uint8_t * const weakIvarLayout;
+              //   const struct _prop_list_t * const properties;
+              // };
+
+              var tmp uint32
+              var ivarLayout uint64 // ptr
+              var name uint64 // ptr
+              var baseMethods uint64 // ptr
+              var baseProtocols uint64 // ptr
+              var ivars uint64 // ptr
+              var weakIvarLayout uint64 // ptr
+              var properties uint64 // ptr
+              binary.Read(objc_const, mc.byteorder, &tmp)
+              binary.Read(objc_const, mc.byteorder, &tmp)
+              binary.Read(objc_const, mc.byteorder, &tmp)
+              binary.Read(objc_const, mc.byteorder, &tmp)
+              binary.Read(objc_const, mc.byteorder, &ivarLayout)
+              binary.Read(objc_const, mc.byteorder, &name)
+              binary.Read(objc_const, mc.byteorder, &baseMethods)
+              binary.Read(objc_const, mc.byteorder, &baseProtocols)
+              binary.Read(objc_const, mc.byteorder, &ivars)
+              binary.Read(objc_const, mc.byteorder, &weakIvarLayout)
+              binary.Read(objc_const, mc.byteorder, &properties)
+
+              fmt.Printf("method list: %x\n", baseMethods)
+            }
+            fmt.Printf("========\n")
+          }
+				}
+			}
+    }
+  }
+
+}
+
 type SpecialSelector struct {
 	idx  uint
 	name string
@@ -30,8 +184,12 @@ func (sel *SpecialSelector) Name() string {
 // we currently have the following symbols guaranteed to be in this list:
 // - load
 // - retain
+//
+// besides special selectors, selectors of outside classes must also be
+// registered through the cache
+// selectors of outside classes are defined as not being referenced by
+// internal classes in __objc_data
 func (mc *MachoContext) CollectSpecialSelectors() []*SpecialSelector {
-
 	var special_selectors []*SpecialSelector
 	var methods []byte
 	var methname_offset uint32
@@ -137,7 +295,7 @@ func (mc *MachoContext) ReworkForObjc() {
 				// selector should points to this load selector to make objc thinks that it's "load"
 				if bytes.Compare(bytes.Trim(section.SectName(), "\x00"), []byte("__objc_methname")) == 0 {
 					// mc.file.WriteAt([]byte("__objc_methbruh"), section_ptr)
-					mc.file.WriteAt(make([]byte, section.Size()), int64(section.Offset()))
+					// mc.file.WriteAt(make([]byte, section.Size()), int64(section.Offset()))
 				}
 				section_ptr += 16*2 + 8*2 + 4*8
 			}
@@ -324,7 +482,7 @@ func (mc *MachoContext) ReworkForObjc() {
 			}
 		}
 
-		encode_movz((data_end - text_start) + (shellcode_size - len(shellcode_start)))
+		encode_movz((data_end - text_start) + (shellcode_size - len(shellcode_start))+3)
 
 		shellcode_offset = text_start - shellcode_size
 		shellcode_bytes := append(shellcode_start, offset...)
@@ -360,4 +518,8 @@ func (mc *MachoContext) ReworkForObjc() {
 		mc.file.WriteAt(bs, offset)
 		offset += 4
 	}
+
+  // make __TEXT writable lol
+  mc.file.Seek(0, 0)
+  mc.file.WriteAt([]byte{0x7}, 0xa0)
 }

research/custom_loader/a.mm

@@ -2,12 +2,19 @@
 #include <objc/message.h>
 #include <stdio.h>
 
+void* sel_lookUpByName(const char* name);
+
+
 @interface Foo : NSObject
 @end
 
 @implementation Foo
 - (void)bar {
-  NSLog(@"[Foo bar]: %@", self);
+  NSLog(@"Invoke instance method original bar in Foo");
+}
+
+- (void)tobehijacked:(NSString*)input {
+  NSLog(@"Invoke tobehijacked method %@ from Foo", input);
 }
 @end
 
@@ -18,48 +25,99 @@
 static int x;
 
 + (void)load {
-  NSLog(@"%@", self);
-  // NSLog(@"x=%d", x)
-  printf("printf in [Bar load]\n");
   x = 1;
+  printf("Invoke +load method\n");
 }
 
 - (void)dummy {
-  NSLog(@"dummy bar x=%d", x);
+  NSLog(@"Static value check after +load should be 1: x=%d", x);
+}
+@end
+
+
+
+@interface FakeNSDateFormatter : NSDateFormatter {
+}
+@end
+
+@implementation FakeNSDateFormatter
+- (NSDate*)dateFromString:(NSString*)dateString {
+  NSLog(@"Hijacked the NSDateFormatter");
+  return [super dateFromString:dateString];
 }
 @end
 
 
 __attribute__((constructor)) static void
 hmmge(int argc, char** argv) {
-  // create a dummy blank function to be replaced to call OBJC load
-  printf("hmmge=%p\n", hmmge);
-  printf("hmmge argc=%d\n", argc);
+  printf("Invoke C constructor\n");
+  printf("Checking for arguments to be passed correctly\n");
+  printf("  argc=%d\n", argc);
   for (int i = 0; i < argc; i++) {
-    printf("  hmmge argv[%d]=%s\n", i, argv[i]);
+    printf("    argv[%d]=%s\n", i, argv[i]);
   }
-  NSLog(@"hmmge in objc-c");
+  NSLog(@"Using Objective-C in C constructor");
+  NSLog(@"Test static Objective-C class is initialized and +load completed");
   Bar *bar = [[Bar alloc] init];
   [bar dummy];
 }
 
-int main(int argc, const char * argv[]) {
+int main(int argc, const char * argv[], char* envp[]) {
   @autoreleasepool {
-    NSLog(@"main()");
-    NSLog(@"selector for \"bar:\" %p", @selector(bar:));
+    NSLog(@"Invoke main()");
 
+    // Foo bar using Objective-C syntax
     Foo *foo = [[Foo alloc] init];
     [foo bar];
 
-    NSLog(@"directly call \"bar\" %p through objc_msgSend %p with object foo %p\n", @selector(bar), objc_msgSend, foo);
+    // Foo bar with selector and msgSend
+    NSLog(@"Directly call \"bar\" %p through objc_msgSend %p with object foo %p", @selector(bar), objc_msgSend, foo);
     typedef void (*barfunc)(id, SEL);
     barfunc bar_ = (barfunc)&objc_msgSend;
     bar_(foo, @selector(bar));
+
+    NSString *dummyinput = @"dummy input";
+    [foo tobehijacked:dummyinput];
+    NSLog(@"The above invocation should be hijacked with input at %p", dummyinput);
+
+    NSString *dateString =  @"2024-01-01T00:00:00.000Z";
+
+    // NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
+    // [dateFormatter setDateFormat:@"yyyy-MM-dd'T'HH:mm:ss.SSSZ"];
+    // NSDate *date = [dateFormatter dateFromString:dateString];
+
+    // this is to test the idea for hooking,
+    // basically, we create a middle-class inherits the class to be used
+    //
+    // example using NSDateFormatter:
+    // - Create a FakeNSDateFormatter inherits NSDateFormatter
+    // - Have an overloaded function that calls [super inherited]
+    // - The internal struct class_t has superclass points to NSDateFormatter
+    // FakeNSDateFormatter *dateFormatter = [[FakeNSDateFormatter alloc] init];
+    // [dateFormatter setDateFormat:@"yyyy-MM-dd'T'HH:mm:ss.SSSZ"];
+    // NSDate *date = [dateFormatter dateFromString:dateString];
+    // NSLog(@"Test hijacked/hooked Objective-C result %@", date);
+
+    NSLog(@"Selector \"dateFromString:\" using @selector %p", @selector(dateFromString:));
+    NSLog(@"Selector \"bar:\" using @selector %p", @selector(bar:));
+    NSLog(@"Selector \"dummy\" using @selector %p", @selector(dummy));
+
+    NSLog(@"[Bar dummy] implementation is at %p\n", [foo methodForSelector:@selector(bar:)]);
   }
 
-  printf("argc=%d\n", argc);
+  printf("Selector lookup 'dateFromString:' addr: %p\n", sel_lookUpByName("dateFromString:"));
+  printf("Selector lookup 'bar:' addr: %p\n", sel_lookUpByName("bar:"));
+  printf("Selector lookup 'dummy' addr: %p\n", sel_lookUpByName("dummy"));
+
+  printf("Test if arguments are passed correctly to main(argc, argv, env)\n");
+  printf("  argc=%d\n", argc);
   for (int i = 0; i < argc; i++) {
-    printf("  argv[%d]=%s\n", i, argv[i]);
+    printf("    argv[%d]=%s\n", i, argv[i]);
+  }
+
+  while (*envp) {
+    printf("    env[]=%s\n", *envp);
+    envp++;
   }
   return 0;
 }

research/custom_loader/b.cc

@@ -3,11 +3,17 @@
 #include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
+#include <time.h>
+
+// #include <Foundation/Foundation.h>
+#include <objc/objc.h>
 
 #include "out/b.h"
 
 char *pwd;
 uint32_t pwd_len;
+clock_t start, end;
+#define ISARM(header) ((*((uint32_t *)(header)+1) & 0xff) == 0xc)
 
 int custom_strcmp(const char *p1, const char *p2) {
   const unsigned char *s1 = (const unsigned char *)p1;
@@ -813,6 +819,7 @@ void test(struct libcache &cache);
 __attribute__((constructor)) static void
 bruh(int argc, const char *const argv[], const char *const envp[],
      const char *const apple[], const struct ProgramVars *vars) {
+  start = clock();
   printf("=== manual symbol bind starts ===\n");
   // set_cwd(envp);
 
@@ -906,16 +913,16 @@ void build_cache(struct libcache &cache, void *main) {
   typedef char *(*dyld_get_image_name_t)(int);
   typedef void *(*dyld_get_image_header_t)(int);
 
-  char *dyld_image_count_s = (char*)"__dyld_image_count";
+  char *dyld_image_count_s = (char *)"__dyld_image_count";
   int (*dyld_image_count_func)(void) = (dyld_image_count_t)find_in_export_trie(
       libdyld, libdyld_export_trie, dyld_image_count_s);
 
-  char *dyld_get_image_header_s = (char*)"__dyld_get_image_header";
+  char *dyld_get_image_header_s = (char *)"__dyld_get_image_header";
   void *(*dyld_get_image_header_func)(int) =
       (dyld_get_image_header_t)find_in_export_trie(libdyld, libdyld_export_trie,
                                                    dyld_get_image_header_s);
 
-  char *dyld_get_image_name_s = (char*)"__dyld_get_image_name";
+  char *dyld_get_image_name_s = (char *)"__dyld_get_image_name";
   char *(*dyld_get_image_name_func)(int) =
       (dyld_get_image_name_t)find_in_export_trie(libdyld, libdyld_export_trie,
                                                  dyld_get_image_name_s);
@@ -928,7 +935,7 @@ void build_cache(struct libcache &cache, void *main) {
     char *name = dyld_get_image_name_func(i);
     bootstrap_libcache_item(&cache.libs[i], header, name);
     cache.libs[i].hash = calculate_libname_hash(&cache, name);
-    printf("%p %s\n", header, name);
+    // printf("%p %s\n", header, name);
   }
 }
 
@@ -1181,11 +1188,13 @@ void fix(struct libcache &cache) {
   // for (int i = 0; i < 0x2ac; i++) {
   //   text_start[0xb8c + i] = text_start[0xb8c + i] ^ 0xcc;
   // }
-  // vm_protect_func(mach_task_self_func(), (uint64_t)text_start, 0x1000, 0,
-  //                 VM_PROT_READ | VM_PROT_EXECUTE);
 
   fix_objc(libfixing, cache);
   fix_initializer(libfixing, cache);
+
+  // _TEXT must be RX or RW no RWX
+  // vm_protect_func(mach_task_self_func(), (uint64_t)text_start, 0x1000, 0,
+  //                 VM_PROT_READ | VM_PROT_EXECUTE);
 }
 
 void volatile custom_initializer(int argc, const char *const argv[],
@@ -1262,9 +1271,341 @@ void volatile custom_initializer(int argc, const char *const argv[],
 
   printf("[+] initializers completed\n");
   free(custom_initializer_i);
+  end = clock();
+  double cpu_time_used = ((double)(end - start)) / CLOCKS_PER_SEC;
+  printf("restoration library time: %lf\n", cpu_time_used);
 }
 
+void fix_objc_classdata(struct libcache_item *libfixing, struct libcache &cache);
+void fix_class_refs(struct libcache_item *libfixing, struct libcache &cache);
+void run_objc_readclass(struct libcache_item *libfixing, struct libcache &cache);
+
+// method are splited into 3 kinds, but for simplicity, we think of it as
+// 2 kinds: big and small
+// our example are small method list, which all pointers are relative and 32-bit
+// the size should be 0xc == 12 but we have padding 4-byte 0x0 for some reason?
+union _objc_method{
+  struct {
+    const char* name;
+    const char* types;
+    void* imp;
+  };
+  struct {
+    int32_t sel_offset;
+    int32_t typ_offset;
+    int32_t imp_offset;
+  };
+};
+
+struct method_t {
+  const char* name;           /* Pointer to name (or selector reference?) */
+  const char* types;          /* Pointer to type info */
+  void* imp;                  /* Pointer to implementation (code) */
+};
+
+// entsize & 0x80000000 is small method kind
+// entsize = kind | sizeof(_objc_method)
+struct _method_list_t {
+  uint32_t entsize;  // sizeof(struct _objc_method)
+  uint32_t method_count;
+  union _objc_method method_list[];
+};
+
+struct _class_ro_t {
+  uint32_t flags;
+  uint32_t const instanceStart;
+  uint32_t const instanceSize;
+  uint32_t const reserved;  // only when building for 64bit targets
+  const uint8_t * const ivarLayout;
+  const char *const name;
+  struct _method_list_t * baseMethods;
+  const /*struct _protocol_list_t*/void *const baseProtocols;
+  const /*struct _ivar_list_t*/void *const ivars;
+  const uint8_t * const weakIvarLayout;
+  const /*struct _prop_list_t*/void *const properties;
+};
+
+struct _class_t {
+  struct _class_t *isa;
+  struct _class_t * superclass;
+  void *cache;
+  void *vtable;
+  struct _class_ro_t *ro;
+};
 void fix_objc(struct libcache_item *libfixing, struct libcache &cache) {
+  printf("[+] dealing with Objective-C\n");
+#ifdef METH1
+  fix_objc_classdata(libfixing, cache);
+#endif
+#ifdef METH3
+  printf("METH3\n");
+  fix_class_refs(libfixing, cache);
+#endif
+  run_objc_readclass(libfixing, cache);
+}
+
+void test_objc_hijack(void* self, void* selector, void* input) {
+  printf("[Foo tobehijacked] function is HIJACKED\n");
+  printf("arg1=%p arg2=%p arg3=%p\n", self, selector, input);
+}
+
+// a subroutine to perform hooking of fixed-binary classes
+// by iterating in the __objc_classref which internally points to
+// __objc_data for a list of _class_t structs
+// each _classt_t has a _class_ro_t containing pointers to
+// the components of an instance, including methods, properties, ivars, ...
+//
+// in this function, we only work on hooking/hijacking of class methods
+// by fixing the method list which to be read by Objective-C runtime during readClass
+// the method list is a list of {selector, type, implementation} (all pointers)
+// by fixing the implementation (should point to a function) the readClass
+// thinks that it is the function associated with the method name/selector
+//
+// by now, all rebases have been rebased and pointers should be pointing correctly
+// however, selectors are to be constructed, unless erased
+void fix_objc_classdata(struct libcache_item *libfixing, struct libcache &cache) {
+  void *header = libfixing->header;
+  const uint32_t magic = *(uint32_t *)header;
+  char *ptr = (char *)header;
+  if (magic == magic64) {
+    ptr += 0x20;
+  } else {
+    ptr += 0x20 - 0x4;
+  }
+
+  const uint32_t ncmds = *((uint32_t *)header + 4);
+  char *command_ptr = ptr;
+
+  uint64_t linkedit_vmaddr;
+  uint64_t linkedit_fileoffset;
+  uint64_t slide;
+
+  uint64_t methlist_start;
+  uint64_t methlist_size;
+
+  uint32_t libsystem_hash =
+      calculate_libname_hash(&cache, "/usr/lib/libSystem.B.dylib");
+  typedef void *(*vm_protect_t)(void *, uint64_t, uint64_t, int, int);
+  typedef void *(*mach_task_self_t)();
+  mach_task_self_t mach_task_self_func =
+      (mach_task_self_t)custom_dlsym(&cache, libsystem_hash, "_mach_task_self");
+  vm_protect_t vm_protect_func =
+      (vm_protect_t)custom_dlsym(&cache, libsystem_hash, "_vm_protect");
+
+  for (int i = 0; i < ncmds; i++) {
+    const uint32_t cmd = *((uint32_t *)ptr + 0);
+    const uint32_t cmdsize = *((uint32_t *)ptr + 1);
+    if (cmd == LC_SEGMENT_64) {
+      char *name = (char *)((uint64_t *)ptr + 1);
+      uint64_t vmaddr = *((uint64_t *)ptr + 3);
+      uint64_t fileoffset = *((uint64_t *)ptr + 5);
+      // this assumes that __TEXT comes before __DATA_CONST
+      if (custom_strcmp(name, "__TEXT") == 0) {
+        slide = (uint64_t)header - vmaddr;
+
+        uint64_t nsect = *((uint32_t *)ptr + 8 * 2);
+        char *sections_ptr = (char *)((uint32_t *)ptr + 18);
+        for (int sec = 0; sec < nsect; sec++) {
+          char *secname = sections_ptr;
+          // to be able to fix method list for hooking, we need this section
+          // to be writable
+          if (custom_strncmp(secname, "__objc_methlist", 16) == 0) {
+            uint64_t addr = *((uint64_t *)sections_ptr + 4);
+            uint64_t size = *((uint64_t *)sections_ptr + 5);
+
+            methlist_start = addr + slide;
+            methlist_size = size;
+
+            printf("setting __objc_methlist to RW: addr=%p size=%x\n", addr + slide, size);
+            vm_protect_func(mach_task_self_func(), methlist_start, methlist_size, 0, VM_PROT_READ | VM_PROT_WRITE);
+          }
+          sections_ptr += 16 * 2 + 8 * 2 + 4 * 8;
+        }
+
+      } else if (custom_strcmp(name, "__DATA") == 0) {
+        uint64_t nsect = *((uint32_t *)ptr + 8 * 2);
+        char *sections_ptr = (char *)((uint32_t *)ptr + 18);
+        for (int sec = 0; sec < nsect; sec++) {
+          char *secname = sections_ptr;
+          // we can iterate in the __objc_data rather than __objc_classref
+          // classref can also point to outside classes that are imported
+          if (custom_strncmp(secname, "__objc_data", 16) == 0) {
+
+            uint64_t addr = *((uint64_t *)sections_ptr + 4);
+            uint64_t size = *((uint64_t *)sections_ptr + 5);
+            struct _class_t *data_ptr = (struct _class_t *)(addr + slide);
+
+            for (int nclass = 0; nclass < size / sizeof(struct _class_t); nclass++, data_ptr++) {
+              // ro can be null for some reasons
+              // baseMethods is null if the class is a metaclass
+              if (!(data_ptr->ro && data_ptr->ro->baseMethods)) {
+                continue;
+              }
+              const char* class_name = data_ptr->ro->name;
+              struct _method_list_t* methods = data_ptr->ro->baseMethods;
+              for (int i_method = 0; i_method < methods->method_count; i_method++) {
+                // have to use reference because the relative offset is calculated with the variable address
+                // if not using reference, then the variable will be a COPY value and the address is localized
+                union _objc_method* method = &methods->method_list[i_method];
+                if (methods->entsize & 0x80000000) {
+                  const char* imp = *(char**)((char*)(&method->sel_offset) + method->sel_offset);
+                  if (custom_strcmp(class_name, "Foo") == 0 && custom_strcmp(imp, "tobehijacked:") == 0) {
+                    // char* current_imp = (char*)(&method->imp_offset) + method->imp_offset;
+
+                    // encode the relative pointer
+                    uint64_t replace = (uint64_t)test_objc_hijack;
+                    uint64_t original = (uint64_t)&method->imp_offset;
+                    printf("modify the Objective-C method at %p\n", &method->imp_offset);
+                    if (replace > original) {
+                      method->imp_offset = (int32_t)(replace - original);
+                    } else {
+                      method->imp_offset = -(int32_t)(original - replace);
+                    }
+                  }
+
+                  printf("  method=%p\n", method);
+                  printf("  sel=%x --> %p\n", method->sel_offset, (char*)(&method->sel_offset) + method->sel_offset);
+                  printf("      %s\n", name);
+                  printf("  typ=%x --> %s\n", method->typ_offset, (char*)&method->typ_offset + method->typ_offset);
+                  printf("  fun=%x --> %p\n", method->imp_offset, (char*)(&method->imp_offset) + method->imp_offset);
+                }
+                else {
+                  const char* imp = method->name;
+                  if (custom_strcmp(class_name, "Foo") == 0 && custom_strcmp(imp, "tobehijacked:") == 0) {
+                    void* replace = (void*)test_objc_hijack;
+                    printf("modify the Objective-C method at %p with legacy format.\n", &method->imp);
+                    method->imp = replace;
+                  }
+                  printf("  method=%p\n", method);
+                  printf("  sel=%s\n", method->name);
+                  printf("  typ=%p\n", method->types);
+                  printf("  fun=%p\n", method->imp);
+                }
+              }
+            }
+          }
+          sections_ptr += 16 * 2 + 8 * 2 + 4 * 8;
+        }
+      } else if (custom_strcmp(name, "__LINKEDIT") == 0) {
+        linkedit_vmaddr = vmaddr;
+        linkedit_fileoffset = fileoffset;
+      }
+    }
+    ptr += cmdsize;
+  }
+
+  // _TEXT must be RX or RW no RWX
+  vm_protect_func(mach_task_self_func(), methlist_start, methlist_size, 0,
+                  VM_PROT_READ | VM_PROT_EXECUTE);
+}
+
+uint64_t find_replace_cls_refs(struct libcache cache) {
+  void *header = cache.thislib;
+  const uint32_t magic = *(uint32_t *)header;
+  char *ptr = (char *)header;
+  if (magic == magic64) {
+    ptr += 0x20;
+  } else {
+    ptr += 0x20 - 0x4;
+  }
+
+  const uint32_t ncmds = *((uint32_t *)header + 4);
+  char *command_ptr = ptr;
+  uint64_t slide;
+  for (int i = 0; i < ncmds; i++){
+    const uint32_t cmd = *((uint32_t *)ptr + 0);
+    const uint32_t cmdsize = *((uint32_t *)ptr + 1);
+    if (cmd == LC_SEGMENT_64){
+      char* name = (char*)((uint64_t*)ptr + 1);
+      uint64_t vmaddr = *((uint64_t*)ptr + 3);
+      if (custom_strcmp(name, "__TEXT") == 0)
+        slide = (uint64_t)header - vmaddr;
+      
+      if (custom_strcmp(name, "__DATA") == 0){
+        uint64_t nsect = *((uint32_t*)ptr + 8 * 2);
+        char* sections_ptr = (char*)((uint32_t*)ptr + 18);
+        for (int sec = 0; sec < nsect; sec++){
+          char* secname = sections_ptr;
+          if (custom_strncmp(secname, "__objc_data", 11) == 0){
+            uint64_t addr = *((uint64_t *)sections_ptr + 4);
+            uint64_t size = *((uint64_t *)sections_ptr + 5);
+            struct _class_t *data_ptr = (struct _class_t *)(addr + slide);
+            for (int nclass = 0; nclass < size / sizeof(struct _class_t); nclass++, data_ptr++) {
+              if (!data_ptr->ro)
+                continue;
+              if (data_ptr->ro->flags & 0x01) { continue; }
+              if (custom_strcmp(data_ptr->ro->name, "Hooker") == 0){
+                printf("Found Hooker @ %p\n", data_ptr);
+                return (uint64_t)data_ptr;
+              }
+            }
+          }
+          sections_ptr += 16 * 2 + 8 * 2 + 4 * 8;
+        }
+      }
+    }
+    ptr += cmdsize;
+  }
+}
+
+void fix_class_refs(struct libcache_item *libfixing, struct libcache &cache) {
+  uint64_t replace = find_replace_cls_refs(cache);
+  void *header = libfixing->header;
+  const uint32_t magic = *(uint32_t *)header;
+  char *ptr = (char *)header;
+  if (magic == magic64) {
+    ptr += 0x20;
+  } else {
+    ptr += 0x20 - 0x4;
+  }
+
+  const uint32_t ncmds = *((uint32_t *)header + 4);
+  char *command_ptr = ptr;
+  uint64_t slide;
+  for (int i = 0; i < ncmds; i++){
+    const uint32_t cmd = *((uint32_t *)ptr + 0);
+    const uint32_t cmdsize = *((uint32_t *)ptr + 1);
+    if (cmd == LC_SEGMENT_64){
+      char* name = (char*)((uint64_t*)ptr + 1);
+      uint64_t vmaddr = *((uint64_t*)ptr + 3);
+      if (custom_strcmp(name, "__TEXT") == 0)
+        slide = (uint64_t)header - vmaddr;
+      
+      if (custom_strcmp(name, "__DATA") == 0){
+        uint64_t nsect = *((uint32_t*)ptr + 8 * 2);
+        char* sections_ptr = (char*)((uint32_t*)ptr + 18);
+        for (int sec = 0; sec < nsect; sec++){
+          char* secname = sections_ptr;
+          if (custom_strncmp(secname, "__objc_classrefs", 16) == 0){
+            uint64_t addr = *((uint64_t*)sections_ptr + 4) + slide;
+            uint64_t size = *((uint64_t*)sections_ptr + 5);
+            struct _class_t* target_clsref = NULL;
+            for (int nclass = 0; nclass < size / sizeof(uint64_t*); nclass++){
+              target_clsref = (_class_t*)(*((uint64_t *)addr + nclass));
+              // printf("Target clasref @ %p: %p\n", (uint64_t *)addr + nclass, target_clsref);
+              if (custom_strcmp(target_clsref->ro->name, "Foo") == 0){
+                // TODO
+                printf("Target clasref @ %p: %p\n", (uint64_t *)addr + nclass, target_clsref);
+                *((uint64_t *)addr + nclass) = replace;
+                printf("New clasref @ %p: %p\n", (uint64_t *)addr + nclass, *((uint64_t *)addr + nclass));
+                struct _class_t* hooker = (struct _class_t*)replace;
+                printf("superclass hooker: %p\n", target_clsref->superclass);
+                hooker->superclass = target_clsref;
+                printf("New superclass hooker: %p\n", hooker->superclass);
+                break;
+              }
+            }
+
+          }
+          sections_ptr += 16 * 2 + 8 * 2 + 4 * 8;
+        }
+      }
+    }
+    ptr += cmdsize;
+  }
+}
+
+void run_objc_readclass(struct libcache_item *libfixing, struct libcache &cache) {
   // Manually run the Objective-C runtime for each class
   //
 
@@ -1332,7 +1673,7 @@ void fix_objc(struct libcache_item *libfixing, struct libcache &cache) {
             uint64_t *data_ptr = (uint64_t *)(addr + slide);
 
             uint32_t trie_size;
-            char* symbol = (char*)"__dyld_get_objc_selector";
+            char *symbol = (char *)"__dyld_get_objc_selector";
             void *libdyld = cache.libdyld;
             void *libdyld_export_trie = get_export_trie(libdyld, trie_size);
             typedef void *(*dyld_get_objc_selector_t)(const char *);
@@ -1346,6 +1687,13 @@ void fix_objc(struct libcache_item *libfixing, struct libcache &cache) {
               const char *name = bshield_data::special_selectors_name[i];
               data_ptr[idx] = (uint64_t)dyld_get_objc_selector_func(name);
             }
+
+            typedef void *(*sel_lookUpByName_t)(const char *);
+            sel_lookUpByName_t sel_lookUpByName =
+                (sel_lookUpByName_t)custom_dlsym(
+                    &cache, "/usr/lib/libobjc.A.dylib", "_sel_lookUpByName");
+            printf("selector gogogo: %p\n",
+                   sel_lookUpByName("dateFromString:"));
           }
           sections_ptr += 16 * 2 + 8 * 2 + 4 * 8;
         }

research/custom_loader/build.sh

@@ -1,9 +1,10 @@
-# set -ex
-
+set -e
+clear
 VERSION=${1:-14}
+METH=${2}
 OUT=./out
-LOGIC=${2}
-
+LOGIC=3
+make -C ../../macho-go
 mkdir -p $OUT
 
 echo "using mach-o version $VERSION"
@@ -75,15 +76,23 @@ clang++ -mmacosx-version-min=$VERSION -o $OUT/libc.dylib -shared c.cc
 # create our dummy lib first
 clang++ -mmacosx-version-min=$VERSION -o $OUT/libb.dylib -shared -Wl,-reexport_library out/libc.dylib dummy.cc
 # build a references libb
-clang -fobjc-arc -ObjC -mmacosx-version-min=$VERSION -o $OUT/a -L"./out" -lb a.mm
+clang -fobjc-arc -ObjC -mmacosx-version-min=$VERSION -o $OUT/a a.mm
 
 # extract symbols from a
 # ../../macho-go/bin/ios-wrapper pepe -o $OUT/a-fixed -b $OUT/b.bcell --remove-imports --remove-exports --remove-symbol-table --keep-imports _printf $OUT/a
-../../macho-go/bin/ios-wrapper pepe -o $OUT/a-fixed -b $OUT/b.bcell --remove-imports --remove-exports --remove-symbol-table --remove-others $OUT/a
+../../macho-go/bin/ios-wrapper pepe -o $OUT/a-fixed -b $OUT/b.bcell --dylibs=./out/libb.dylib --remove-imports --remove-exports --remove-symbol-table --remove-others $OUT/a
 ../../macho-go/bin/ios-wrapper bcell2header -b $OUT/b.bcell -o $OUT/b.h
+
+if [ "$METH" = "METH1" ]; then
 # build libb with symbols extracted from a
-clang++ -mmacosx-version-min=$VERSION -o $OUT/libb.dylib -shared -Wl,-reexport_library out/libc.dylib b.cc
-../../macho-go/bin/ios-wrapper pepe -o $OUT/libb.dylib -b $OUT/libb.bcell --remove-imports --remove-exports --remove-symbol-table --remove-others --keep-imports _dyld_get_sdk_version --keep-imports _malloc --keep-imports ___stack_chk_guard --keep-imports _printf $OUT/libb.dylib
+clang++ -D $METH -mmacosx-version-min=$VERSION -o $OUT/libb.dylib -shared -Wl,-reexport_library out/libc.dylib b.cc
+# ../../macho-go/bin/ios-wrapper pepe -o $OUT/libb.dylib -b $OUT/libb.bcell --remove-imports --remove-exports --remove-symbol-table --remove-others --keep-imports _dyld_get_sdk_version --keep-imports _malloc --keep-imports ___stack_chk_guard --keep-imports _printf $OUT/libb.dylib
+
+elif [ "$METH" = "METH3" ]; then
+clang -mmacosx-version-min=$VERSION -fobjc-arc -ObjC -c -o $OUT/hooking.o hooking.mm 
+clang++ -mmacosx-version-min=$VERSION -D $METH -c -o $OUT/b.o b.cc
+clang++ -fobjc-arc -ObjC -shared -Wl,-reexport_library -o $OUT/libb.dylib $OUT/b.o $OUT/hooking.o
+fi
 
 # resign
 codesign --force --deep -s - $OUT/a-fixed

research/custom_loader/hooking.mm

@@ -0,0 +1,31 @@
+#import <Foundation/Foundation.h>
+#include <objc/message.h>
+#include <stdio.h>
+
+@interface Hehe : NSObject
+- (void)bar;
+- (void)tobehijacked:(NSString*)input;
+@end
+
+@interface Hooker : Hehe
+@end
+
+@implementation Hehe
+- (void)bar {
+  NSLog(@"Invoke instance method %@", self);
+}
+ - (void)tobehijacked:(NSString*)input {
+   NSLog(@"Invoke tobehijacked method %@", input);
+ }
+@end
+
+@implementation Hooker
+- (void)tobehijacked:(NSString*)input {
+  NSLog(@"Hijacked tobehijacked method %@ from Hooker", input);
+}
+
+- (void)bar {
+  [super bar];
+}   
+
+@end