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 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 33 static void set_eflags(unsigned long eflags) 34 { 35 asm volatile ("push" WIDTH " %0\n\tpopf" WIDTH 36 : : "rm" (eflags) : "flags"); 37 } 38 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 51 static void sigtrap(int sig, siginfo_t *si, void *ctx_void) 52 { 53 } 54 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 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 71 int 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 } 88