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@ucotta
Forked from DGivney/httpd.asm
Created March 19, 2021 19:00
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section .text
global _start
_start:
xor eax, eax ; init eax 0
xor ebx, ebx ; init ebx 0
xor esi, esi ; init esi 0
jmp _socket ; jmp to _socket
_socket_call:
mov al, 0x66 ; invoke SYS_SOCKET (kernel opcode 102)
inc byte bl ; increment bl (1=socket, 2=bind, 3=listen, 4=accept)
mov ecx, esp ; move address arguments struct into ecx
int 0x80 ; call SYS_SOCKET
jmp esi ; esi is loaded with a return address each call to _socket_call
_socket:
push byte 6 ; push 6 onto the stack (IPPROTO_TCP)
push byte 1 ; push 1 onto the stack (SOCK_STREAM)
push byte 2 ; push 2 onto the stack (PF_INET)
mov esi, _bind ; move address of _bind into ESI
jmp _socket_call ; jmp to _socket_call
_bind:
mov edi, eax ; move return value of SYS_SOCKET into edi (file descriptor for new socket, or -1 on error)
xor edx, edx ; init edx 0
push dword edx ; end struct on stack (arguments get pushed in reverse order)
push word 0x6022 ; move 24610 dec onto stack
push word bx ; move 1 dec onto stack AF_FILE
mov ecx, esp ; move address of stack pointer into ecx
push byte 0x10 ; move 16 dec onto stack
push ecx ; push the address of arguments onto stack
push edi ; push the file descriptor onto stack
mov esi, _listen ; move address of _listen onto stack
jmp _socket_call ; jmp to _socket_call
_listen:
inc bl ; bl = 3
push byte 0x01 ; move 1 onto stack (max queue length argument)
push edi ; push the file descriptor onto stack
mov esi, _accept ; move address of _accept onto stack
jmp _socket_call ; jmp to socket call
_accept:
push edx ; push 0 dec onto stack (address length argument)
push edx ; push 0 dec onto stack (address argument)
push edi ; push the file descriptor onto stack
mov esi, _fork ; move address of _fork onto stack
jmp _socket_call ; jmp to _socket_call
_fork:
mov esi, eax ; move return value of SYS_SOCKET into esi (file descriptor for accepted socket, or -1 on error)
mov al, 0x02 ; invoke SYS_FORK (kernel opcode 2)
int 0x80 ; call SYS_FORK
test eax, eax ; if return value of SYS_FORK in eax is zero we are in the child process
jz _write ; jmp in child process to _write
xor eax, eax ; init eax 0
xor ebx, ebx ; init ebx 0
mov bl, 0x02 ; move 2 dec in ebx lower bits
jmp _listen ; jmp in parent process to _listen
_write:
mov ebx, esi ; move file descriptor into ebx (accepted socket id)
push edx ; push 0 dec onto stack then push a bunch of ascii (http headers & reponse body)
push dword 0x0a0d3e31 ; [\n][\r]>1
push dword 0x682f3c21 ; h/<!
push dword 0x64334e77 ; d3Nw
push dword 0x503e3168 ; P>1h
push dword 0x3c0a0d0a ; <[\n][\r][\n]
push dword 0x0d6c6d74 ; [\r]lmt
push dword 0x682f7478 ; h/tx
push dword 0x6574203a ; et :
push dword 0x65707954 ; epyT
push dword 0x2d746e65 ; -tne
push dword 0x746e6f43 ; tnoC
push dword 0x0a4b4f20 ; \nKO
push dword 0x30303220 ; 002
push dword 0x302e312f ; 0.1/
push dword 0x50545448 ; PTTH
mov al, 0x04 ; invoke SYS_WRITE (kernel opcode 4)
mov ecx, esp ; move address of stack arguments into ecx
mov dl, 64 ; move 64 dec into edx lower bits (length in bytes to write)
int 0x80 ; call SYS_WRITE
_close:
mov al, 6 ; invoke SYS_CLOSE (kernel opcode 6)
mov ebx, esi ; move esi into ebx (accepted socket file descriptor)
int 0x80 ; call SYS_CLOSE
mov al, 6 ; invoke SYS_CLOSE (kernel opcode 6)
mov ebx, edi ; move edi into ebx (new socket file descriptor)
int 0x80 ; call SYS_CLOSE
_exit:
mov eax, 0x01 ; invoke SYS_EXIT (kernel opcode 1)
xor ebx, ebx ; 0 errors
int 0x80 ; call SYS_EXIT
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