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
17#include "helpers.h"
18
19static unsigned int nerrs;
20
21static void sethandler(int sig, void (*handler)(int, siginfo_t *, void *),
22		       int flags)
23{
24	struct sigaction sa;
25	memset(&sa, 0, sizeof(sa));
26	sa.sa_sigaction = handler;
27	sa.sa_flags = SA_SIGINFO | flags;
28	sigemptyset(&sa.sa_mask);
29	if (sigaction(sig, &sa, 0))
30		err(1, "sigaction");
31}
32
33static void sigtrap(int sig, siginfo_t *si, void *ctx_void)
34{
35}
36
37static void do_it(unsigned long extraflags)
38{
39	unsigned long flags;
40
41	set_eflags(get_eflags() | extraflags);
42	syscall(SYS_getpid);
43	flags = get_eflags();
44	set_eflags(X86_EFLAGS_IF | X86_EFLAGS_FIXED);
45	if ((flags & extraflags) == extraflags) {
46		printf("[OK]\tThe syscall worked and flags are still set\n");
47	} else {
48		printf("[FAIL]\tThe syscall worked but flags were cleared (flags = 0x%lx but expected 0x%lx set)\n",
49		       flags, extraflags);
50		nerrs++;
51	}
52}
53
54int main(void)
55{
56	printf("[RUN]\tSet NT and issue a syscall\n");
57	do_it(X86_EFLAGS_NT);
58
59	printf("[RUN]\tSet AC and issue a syscall\n");
60	do_it(X86_EFLAGS_AC);
61
62	printf("[RUN]\tSet NT|AC and issue a syscall\n");
63	do_it(X86_EFLAGS_NT | X86_EFLAGS_AC);
64
65	/*
66	 * Now try it again with TF set -- TF forces returns via IRET in all
67	 * cases except non-ptregs-using 64-bit full fast path syscalls.
68	 */
69
70	sethandler(SIGTRAP, sigtrap, 0);
71
72	printf("[RUN]\tSet TF and issue a syscall\n");
73	do_it(X86_EFLAGS_TF);
74
75	printf("[RUN]\tSet NT|TF and issue a syscall\n");
76	do_it(X86_EFLAGS_NT | X86_EFLAGS_TF);
77
78	printf("[RUN]\tSet AC|TF and issue a syscall\n");
79	do_it(X86_EFLAGS_AC | X86_EFLAGS_TF);
80
81	printf("[RUN]\tSet NT|AC|TF and issue a syscall\n");
82	do_it(X86_EFLAGS_NT | X86_EFLAGS_AC | X86_EFLAGS_TF);
83
84	/*
85	 * Now try DF.  This is evil and it's plausible that we will crash
86	 * glibc, but glibc would have to do something rather surprising
87	 * for this to happen.
88	 */
89	printf("[RUN]\tSet DF and issue a syscall\n");
90	do_it(X86_EFLAGS_DF);
91
92	printf("[RUN]\tSet TF|DF and issue a syscall\n");
93	do_it(X86_EFLAGS_TF | X86_EFLAGS_DF);
94
95	return nerrs == 0 ? 0 : 1;
96}
97