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 <string.h>
21 #include <signal.h>
22 #include <err.h>
23 #include <sys/syscall.h>
24 #include <asm/processor-flags.h>
25
26 #ifdef __x86_64__
27 # define WIDTH "q"
28 #else
29 # define WIDTH "l"
30 #endif
31
32 static unsigned int nerrs;
33
34 static unsigned long get_eflags(void)
35 {
36 unsigned long eflags;
37 asm volatile ("pushf" WIDTH "\n\tpop" WIDTH " %0" : "=rm" (eflags));
38 return eflags;
39 }
40
41 static void set_eflags(unsigned long eflags)
42 {
43 asm volatile ("push" WIDTH " %0\n\tpopf" WIDTH
44 : : "rm" (eflags) : "flags");
45 }
46
47 static void sethandler(int sig, void (*handler)(int, siginfo_t *, void *),
48 int flags)
49 {
50 struct sigaction sa;
51 memset(&sa, 0, sizeof(sa));
52 sa.sa_sigaction = handler;
53 sa.sa_flags = SA_SIGINFO | flags;
54 sigemptyset(&sa.sa_mask);
55 if (sigaction(sig, &sa, 0))
56 err(1, "sigaction");
57 }
58
59 static void sigtrap(int sig, siginfo_t *si, void *ctx_void)
60 {
61 }
62
63 static void do_it(unsigned long extraflags)
64 {
65 unsigned long flags;
66
67 set_eflags(get_eflags() | extraflags);
68 syscall(SYS_getpid);
69 flags = get_eflags();
70 if ((flags & extraflags) == extraflags) {
71 printf("[OK]\tThe syscall worked and flags are still set\n");
72 } else {
73 printf("[FAIL]\tThe syscall worked but flags were cleared (flags = 0x%lx but expected 0x%lx set)\n",
74 flags, extraflags);
75 nerrs++;
76 }
77 }
78
79 int main(void)
80 {
81 printf("[RUN]\tSet NT and issue a syscall\n");
82 do_it(X86_EFLAGS_NT);
83
84 /*
85 * Now try it again with TF set -- TF forces returns via IRET in all
86 * cases except non-ptregs-using 64-bit full fast path syscalls.
87 */
88
89 sethandler(SIGTRAP, sigtrap, 0);
90
91 printf("[RUN]\tSet NT|TF and issue a syscall\n");
92 do_it(X86_EFLAGS_NT | X86_EFLAGS_TF);
93
94 return nerrs == 0 ? 0 : 1;
95 }
96
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