Linux kernel mirror (for testing)
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linux
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
24static unsigned int nerrs;
25
26static 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
33static void set_eflags(unsigned long eflags)
34{
35 asm volatile ("push" WIDTH " %0\n\tpopf" WIDTH
36 : : "rm" (eflags) : "flags");
37}
38
39static 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
51static void sigtrap(int sig, siginfo_t *si, void *ctx_void)
52{
53}
54
55static 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
71int 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}