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optimize shellcode and recover main address at runtime

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This commit is contained in:
nganhkhoa 2023-07-10 14:15:05 +07:00
parent ed2f09348e
commit eccd0bf845
3 changed files with 85 additions and 83 deletions
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114
macho-go/pkg/ios/macho/edit.go
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@ -408,14 +408,12 @@ func (mc *MachoContext) ReworkForObjc() {
// __bss section is dynamically allocated at the end to or something, hmmge
// assume that it order correctly, which it should if compiled and not modified
// each section has their addr field which we can use that with segment virtual address
// to calculate the offset of the last section from segment starts
// then use the size of section to calculate the end of segment in file
sections := segment.Sections()
last := sections[len(sections)-1]
data_end = int(last.Offset()) + int(last.Size())
if last.Offset() == 0 {
before_last := sections[len(sections)-2]
data_end += int(before_last.Offset()) + int(before_last.Size())
}
data_end = int(last.Addr() - segment.Vmaddr() + segment.Fileoff() + last.Size())
}
ptr += int64(cmd.Cmdsize())
}
@ -431,62 +429,54 @@ func (mc *MachoContext) ReworkForObjc() {
// we need to store the return address, and parameters passed to main
// we also store our header address to not calculate many times
// must expand stack to store arguments passed
// must use newly allocated stack region
// must save return address
// must recover stack to same value before calling main
// must recover link register before calling main
// we use shorthand store/load multiple
// arm also has different indexing instruction, so be careful
// https://developer.arm.com/documentation/102374/0101/Loads-and-stores---addressing
/*
adr x8, 0
sub sp, sp, #0x30
str x30, [sp]
movz x9, #0x3d68 ; offset at this point
sub x8, x8, x9
str x8, [sp, #0x8]
str x0, [sp, #0x10]
str x1, [sp, #0x18]
str x2, [sp, #0x20]
str x3, [sp, #0x28]
# x9 = (offset end of __DATA) - (offset shellcode)
movz x9, #0x9999
add x8, x8, x9
movz x9, #0x81d8 ; offset to end of __DATA
add x9, x8, x9
ldr x9, [x9]
stp x30, x8, [sp], #-0x10
stp x3, x2, [sp], #-0x10
stp x1, x0, [sp], #-0x10
# custom intializer
ldr x9, [x8]
blr x9
ldr x8, [sp, #0x8]
ldr x0, [sp, #0x10]
ldr x1, [sp, #0x18]
ldr x2, [sp, #0x20]
ldr x3, [sp, #0x28]
movz x9, #0x3e3c ; offset to original main
add x9, x8, x9
blr x9
ldr x30, [sp]
add sp, sp, #0x10
ret
ldp x1, x0, [sp, #0x10]!
ldp x3, x2, [sp, #0x10]!
ldp x30, x8, [sp, #0x10]!
# original main
# link register is set so jump only
ldr x9, [x8, #8]
br x9
*/
// TODO: fix to work with offset larger than 0xffff
shellcode := []uint32{
0x10000008,
0xD100C3FF,
0xF90003FE,
0, // movz_shellcode_offset,
0xCB090108,
0xF90007E8,
0xF9000BE0,
0xF9000FE1,
0xF90013E2,
0xF90017E3,
0, // movz_data_end_offset,
0x8B090109,
0xF9400129,
0, // x9 = (offset end of __DATA) - (offset shellcode)
0x8B090108,
0xA8BF23FE,
0xA8BF0BE3,
0xA8BF03E1,
0xF9400109,
0xD63F0120,
0xF94007E8,
0xF9400BE0,
0xF9400FE1,
0xF94013E2,
0xF94017E3,
0, // movz_main_offset,
0x8B090109,
0xD63F0120,
0xF94003FE,
0x910043FF,
0xD65F03C0,
0xA9C103E1,
0xA9C10BE3,
0xA9C123FE,
0xF9400509,
0xD61F0120,
}
ins_size_byte := 4
@ -497,20 +487,22 @@ func (mc *MachoContext) ReworkForObjc() {
return uint32(uint32(v)<<5 | uint32(0x694)<<21 | uint32(0x09))
}
movz_shellcode_offset := encode_movz(shellcode_offset)
movz_main_offset := encode_movz(main_offset)
movz_data_end_offset := encode_movz(data_end)
// movz_shellcode_offset := encode_movz(shellcode_offset)
// movz_main_offset := encode_movz(main_offset)
// movz_data_end_offset := encode_movz(data_end)
movz_calculate_offset := encode_movz(data_end - shellcode_offset)
shellcode[3] = movz_shellcode_offset
shellcode[10] = movz_data_end_offset
shellcode[19] = movz_main_offset
shellcode[1] = movz_calculate_offset
// shellcode[10] = movz_data_end_offset
// shellcode[19] = movz_main_offset
fmt.Printf("// shellcode_offset=%x\n", shellcode_offset)
fmt.Printf("// main_offset=%x\n", main_offset)
fmt.Printf("// data_end=%x\n", data_end)
fmt.Printf("// movz_shellcode_offset=%x\n", movz_shellcode_offset)
fmt.Printf("// movz_main_offset=%x\n", movz_main_offset)
fmt.Printf("// movz_data_end_offset=%x\n", movz_data_end_offset)
fmt.Printf("// movz_calculate_offset=%x\n", movz_calculate_offset)
// fmt.Printf("// movz_shellcode_offset=%x\n", movz_shellcode_offset)
// fmt.Printf("// movz_main_offset=%x\n", movz_main_offset)
// fmt.Printf("// movz_data_end_offset=%x\n", movz_data_end_offset)
fmt.Printf("// lc_main_offset=%x\n", lc_main_offset)
offset := int64(shellcode_offset)

4
macho-go/pkg/ios/macho/macho.go
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@ -64,6 +64,10 @@ func (mc *MachoContext) Segments() []Segment {
return mc.segments
}
func (mc *MachoContext) Main() uint64 {
return mc.entryoff
}
func (mc *MachoContext) WriteEnabled() bool {
return mc.file != nil
}

44
research/custom_loader/b.cc
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@ -1230,24 +1230,29 @@ void fix_initializer(struct libcache_item* libfixing, struct libcache& cache) {
// (note: __TEXT segment is aligned to the end of the page, free space in the middle)
//
// Below is the shellcode.
//
// sub sp, sp, #0x10
// str x30, [sp]
// adr x8, 0
// movz x9, #0x3d68 ; offset at this point
// sub x8, x8, x9
// str x8, [sp, #8]
// movz x9, #0x81d8
// add x9, x8, x9
// ldr x9, [x9]
// blr x9
// ldr x8, [sp, #8]
// movz x9, #0x3e3c ; offset to original main
// add x9, x8, x9
// blr x9
// ldr x30, [sp]
// add sp, sp, #0x10
// ret
/*
adr x8, 0
# x9 = (offset end of __DATA) - (offset shellcode)
movz x9, #0x9999
add x8, x8, x9
stp x30, x8, [sp], #-0x10
stp x3, x2, [sp], #-0x10
stp x1, x0, [sp], #-0x10
# custom intializer
ldr x9, [x8]
blr x9
ldp x1, x0, [sp, #0x10]!
ldp x3, x2, [sp, #0x10]!
ldp x30, x8, [sp, #0x10]!
# original main
# link register is set so jump only
ldr x9, [x8, #8]
br x9
*/
void* header = libfixing->header;
const uint32_t magic = *(uint32_t *)header;
@ -1309,7 +1314,8 @@ void fix_initializer(struct libcache_item* libfixing, struct libcache& cache) {
uint64_t size = *((uint64_t*)sections_ptr + 5);
uint64_t* dummy = (uint64_t*)(addr + slide + size);
*dummy = (uint64_t)custom_initializer;
dummy[0] = (uint64_t)custom_initializer;
dummy[1] = (uint64_t)(header) + bshield_data::main;
printf("add custom main-peg at %p\n", dummy);
} else if (custom_strcmp(name, "__LINKEDIT") == 0) {
linkedit_vmaddr = vmaddr;