tools/testing/selftests/x86/syscall_nt.c

   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 }