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
29static 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
36static void set_eflags(unsigned long eflags)
37{
38	asm volatile ("push" WIDTH " %0\n\tpopf" WIDTH
39		      : : "rm" (eflags) : "flags");
40}
41
42int 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