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 17 #include "helpers.h" 18 19 static unsigned int nerrs; 20 21 static void sethandler(int sig, void (*handler)(int, siginfo_t *, void *), 22 int flags) 23 { 24 struct sigaction sa; 25 memset(&sa, 0, sizeof(sa)); 26 sa.sa_sigaction = handler; 27 sa.sa_flags = SA_SIGINFO | flags; 28 sigemptyset(&sa.sa_mask); 29 if (sigaction(sig, &sa, 0)) 30 err(1, "sigaction"); 31 } 32 33 static void sigtrap(int sig, siginfo_t *si, void *ctx_void) 34 { 35 } 36 37 static void do_it(unsigned long extraflags) 38 { 39 unsigned long flags; 40 41 set_eflags(get_eflags() | extraflags); 42 syscall(SYS_getpid); 43 flags = get_eflags(); 44 set_eflags(X86_EFLAGS_IF | X86_EFLAGS_FIXED); 45 if ((flags & extraflags) == extraflags) { 46 printf("[OK]\tThe syscall worked and flags are still set\n"); 47 } else { 48 printf("[FAIL]\tThe syscall worked but flags were cleared (flags = 0x%lx but expected 0x%lx set)\n", 49 flags, extraflags); 50 nerrs++; 51 } 52 } 53 54 int main(void) 55 { 56 printf("[RUN]\tSet NT and issue a syscall\n"); 57 do_it(X86_EFLAGS_NT); 58 59 printf("[RUN]\tSet AC and issue a syscall\n"); 60 do_it(X86_EFLAGS_AC); 61 62 printf("[RUN]\tSet NT|AC and issue a syscall\n"); 63 do_it(X86_EFLAGS_NT | X86_EFLAGS_AC); 64 65 /* 66 * Now try it again with TF set -- TF forces returns via IRET in all 67 * cases except non-ptregs-using 64-bit full fast path syscalls. 68 */ 69 70 sethandler(SIGTRAP, sigtrap, 0); 71 72 printf("[RUN]\tSet TF and issue a syscall\n"); 73 do_it(X86_EFLAGS_TF); 74 75 printf("[RUN]\tSet NT|TF and issue a syscall\n"); 76 do_it(X86_EFLAGS_NT | X86_EFLAGS_TF); 77 78 printf("[RUN]\tSet AC|TF and issue a syscall\n"); 79 do_it(X86_EFLAGS_AC | X86_EFLAGS_TF); 80 81 printf("[RUN]\tSet NT|AC|TF and issue a syscall\n"); 82 do_it(X86_EFLAGS_NT | X86_EFLAGS_AC | X86_EFLAGS_TF); 83 84 /* 85 * Now try DF. This is evil and it's plausible that we will crash 86 * glibc, but glibc would have to do something rather surprising 87 * for this to happen. 88 */ 89 printf("[RUN]\tSet DF and issue a syscall\n"); 90 do_it(X86_EFLAGS_DF); 91 92 printf("[RUN]\tSet TF|DF and issue a syscall\n"); 93 do_it(X86_EFLAGS_TF | X86_EFLAGS_DF); 94 95 return nerrs == 0 ? 0 : 1; 96 } 97