Systemsicherheit/Assignment 5 - Software Security - Teil 1/syscalling/code.asm
2024-06-08 18:12:30 +02:00

58 lines
2.1 KiB
NASM

; define some macros
%define O_RDONLY 00000000o
%define O_WRONLY 00000001o
%define O_RDWR 00000002o
%define O_CREAT 00000100o
%define O_TRUNC 00001000o
%define S_IRUSR 00000400o
%define S_IWUSR 00000200o
section .data
path: db "/home/user/nachricht", 0
greeting: db "hidad!", 0
; https://stackoverflow.com/a/45386640
length equ $ - greeting ; Length of greeting message
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; https://chromium.googlesource.com/chromiumos/docs/+/master/constants/syscalls.md#x86-32_bit;
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section .text
global _start
_start:
call _open ; open file
call _write ; write to file
call _close ; close file
call _exit ; exit without errors
; https://www.man7.org/linux/man-pages/man2/open.2.html
_open:
mov eax, 0x05 ; syscall number for 'open'
mov ebx, path ; pointer to the path string
mov ecx, O_CREAT ; open the file if it doesn't exist
xor ecx, O_WRONLY ; open the file in write-only mode
mov edx, S_IRUSR ; permissions for the file
int 0x80 ; call kernel
; https://man7.org/linux/man-pages/man2/write.2.html
_write:
mov ebx, eax ; file descriptor returned by 'open'
mov eax, 0x04 ; syscall number for 'write'
mov ecx, greeting ; pointer to the greeting message
mov edx, length ; length of the greeting message
sub edx, 0x01 ; length of the greeting message without null byte
int 0x80 ; call kernel
; https://man7.org/linux/man-pages/man2/close.2.html
_close:
mov eax, 0x06 ; syscall number for 'close'
int 0x80 ; call kernel
; https://man7.org/linux/man-pages/man2/exit.2.html
_exit:
mov eax, 1 ; syscall number for 'exit'
mov ebx, 0 ; exit status
int 0x80 ; call kernel
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