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