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
get_eflags(void)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
set_eflags(unsigned long eflags)33 static void set_eflags(unsigned long eflags)
34 {
35 asm volatile ("push" WIDTH " %0\n\tpopf" WIDTH
36 : : "rm" (eflags) : "flags");
37 }
38
sethandler(int sig,void (* handler)(int,siginfo_t *,void *),int flags)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
sigtrap(int sig,siginfo_t * si,void * ctx_void)51 static void sigtrap(int sig, siginfo_t *si, void *ctx_void)
52 {
53 }
54
do_it(unsigned long extraflags)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 set_eflags(X86_EFLAGS_IF | X86_EFLAGS_FIXED);
63 if ((flags & extraflags) == extraflags) {
64 printf("[OK]\tThe syscall worked and flags are still set\n");
65 } else {
66 printf("[FAIL]\tThe syscall worked but flags were cleared (flags = 0x%lx but expected 0x%lx set)\n",
67 flags, extraflags);
68 nerrs++;
69 }
70 }
71
main(void)72 int main(void)
73 {
74 printf("[RUN]\tSet NT and issue a syscall\n");
75 do_it(X86_EFLAGS_NT);
76
77 /*
78 * Now try it again with TF set -- TF forces returns via IRET in all
79 * cases except non-ptregs-using 64-bit full fast path syscalls.
80 */
81
82 sethandler(SIGTRAP, sigtrap, 0);
83
84 printf("[RUN]\tSet NT|TF and issue a syscall\n");
85 do_it(X86_EFLAGS_NT | X86_EFLAGS_TF);
86
87 return nerrs == 0 ? 0 : 1;
88 }
89