1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3  * syscall_nt.c - checks syscalls with NT set
4  * Copyright (c) 2014-2015 Andrew Lutomirski
5  *
6  * Some obscure user-space code requires the ability to make system calls
7  * with FLAGS.NT set.  Make sure it works.
8  */
9 
10 #include <stdio.h>
11 #include <unistd.h>
12 #include <string.h>
13 #include <signal.h>
14 #include <err.h>
15 #include <sys/syscall.h>
16 #include <asm/processor-flags.h>
17 
18 #ifdef __x86_64__
19 # define WIDTH "q"
20 #else
21 # define WIDTH "l"
22 #endif
23 
24 static unsigned int nerrs;
25 
26 static unsigned long get_eflags(void)
27 {
28 	unsigned long eflags;
29 	asm volatile ("pushf" WIDTH "\n\tpop" WIDTH " %0" : "=rm" (eflags));
30 	return eflags;
31 }
32 
33 static void set_eflags(unsigned long eflags)
34 {
35 	asm volatile ("push" WIDTH " %0\n\tpopf" WIDTH
36 		      : : "rm" (eflags) : "flags");
37 }
38 
39 static void sethandler(int sig, void (*handler)(int, siginfo_t *, void *),
40 		       int flags)
41 {
42 	struct sigaction sa;
43 	memset(&sa, 0, sizeof(sa));
44 	sa.sa_sigaction = handler;
45 	sa.sa_flags = SA_SIGINFO | flags;
46 	sigemptyset(&sa.sa_mask);
47 	if (sigaction(sig, &sa, 0))
48 		err(1, "sigaction");
49 }
50 
51 static void sigtrap(int sig, siginfo_t *si, void *ctx_void)
52 {
53 }
54 
55 static void do_it(unsigned long extraflags)
56 {
57 	unsigned long flags;
58 
59 	set_eflags(get_eflags() | extraflags);
60 	syscall(SYS_getpid);
61 	flags = get_eflags();
62 	if ((flags & extraflags) == extraflags) {
63 		printf("[OK]\tThe syscall worked and flags are still set\n");
64 	} else {
65 		printf("[FAIL]\tThe syscall worked but flags were cleared (flags = 0x%lx but expected 0x%lx set)\n",
66 		       flags, extraflags);
67 		nerrs++;
68 	}
69 }
70 
71 int main(void)
72 {
73 	printf("[RUN]\tSet NT and issue a syscall\n");
74 	do_it(X86_EFLAGS_NT);
75 
76 	/*
77 	 * Now try it again with TF set -- TF forces returns via IRET in all
78 	 * cases except non-ptregs-using 64-bit full fast path syscalls.
79 	 */
80 
81 	sethandler(SIGTRAP, sigtrap, 0);
82 
83 	printf("[RUN]\tSet NT|TF and issue a syscall\n");
84 	do_it(X86_EFLAGS_NT | X86_EFLAGS_TF);
85 
86 	return nerrs == 0 ? 0 : 1;
87 }
88