1 /* 2 * syscall_nt.c - checks syscalls with NT set 3 * Copyright (c) 2014-2015 Andrew Lutomirski 4 * 5 * This program is free software; you can redistribute it and/or modify 6 * it under the terms and conditions of the GNU General Public License, 7 * version 2, as published by the Free Software Foundation. 8 * 9 * This program is distributed in the hope it will be useful, but 10 * WITHOUT ANY WARRANTY; without even the implied warranty of 11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 12 * General Public License for more details. 13 * 14 * Some obscure user-space code requires the ability to make system calls 15 * with FLAGS.NT set. Make sure it works. 16 */ 17 18 #include <stdio.h> 19 #include <unistd.h> 20 #include <sys/syscall.h> 21 #include <asm/processor-flags.h> 22 23 #ifdef __x86_64__ 24 # define WIDTH "q" 25 #else 26 # define WIDTH "l" 27 #endif 28 29 static unsigned long get_eflags(void) 30 { 31 unsigned long eflags; 32 asm volatile ("pushf" WIDTH "\n\tpop" WIDTH " %0" : "=rm" (eflags)); 33 return eflags; 34 } 35 36 static void set_eflags(unsigned long eflags) 37 { 38 asm volatile ("push" WIDTH " %0\n\tpopf" WIDTH 39 : : "rm" (eflags) : "flags"); 40 } 41 42 int main() 43 { 44 printf("[RUN]\tSet NT and issue a syscall\n"); 45 set_eflags(get_eflags() | X86_EFLAGS_NT); 46 syscall(SYS_getpid); 47 if (get_eflags() & X86_EFLAGS_NT) { 48 printf("[OK]\tThe syscall worked and NT is still set\n"); 49 return 0; 50 } else { 51 printf("[FAIL]\tThe syscall worked but NT was cleared\n"); 52 return 1; 53 } 54 } 55