1/* 2 * entry_from_vm86.c - tests kernel entries from vm86 mode 3 * Copyright (c) 2014-2015 Andrew Lutomirski 4 * 5 * This exercises a few paths that need to special-case vm86 mode. 6 * 7 * GPL v2. 8 */ 9 10#define _GNU_SOURCE 11 12#include <assert.h> 13#include <stdlib.h> 14#include <sys/syscall.h> 15#include <sys/signal.h> 16#include <sys/ucontext.h> 17#include <unistd.h> 18#include <stdio.h> 19#include <string.h> 20#include <inttypes.h> 21#include <sys/mman.h> 22#include <err.h> 23#include <stddef.h> 24#include <stdbool.h> 25#include <errno.h> 26#include <sys/vm86.h> 27 28static unsigned long load_addr = 0x10000; 29static int nerrs = 0; 30 31static void sethandler(int sig, void (*handler)(int, siginfo_t *, void *), 32 int flags) 33{ 34 struct sigaction sa; 35 memset(&sa, 0, sizeof(sa)); 36 sa.sa_sigaction = handler; 37 sa.sa_flags = SA_SIGINFO | flags; 38 sigemptyset(&sa.sa_mask); 39 if (sigaction(sig, &sa, 0)) 40 err(1, "sigaction"); 41} 42 43static void clearhandler(int sig) 44{ 45 struct sigaction sa; 46 memset(&sa, 0, sizeof(sa)); 47 sa.sa_handler = SIG_DFL; 48 sigemptyset(&sa.sa_mask); 49 if (sigaction(sig, &sa, 0)) 50 err(1, "sigaction"); 51} 52 53static sig_atomic_t got_signal; 54 55static void sighandler(int sig, siginfo_t *info, void *ctx_void) 56{ 57 ucontext_t *ctx = (ucontext_t*)ctx_void; 58 59 if (ctx->uc_mcontext.gregs[REG_EFL] & X86_EFLAGS_VM || 60 (ctx->uc_mcontext.gregs[REG_CS] & 3) != 3) { 61 printf("[FAIL]\tSignal frame should not reflect vm86 mode\n"); 62 nerrs++; 63 } 64 65 const char *signame; 66 if (sig == SIGSEGV) 67 signame = "SIGSEGV"; 68 else if (sig == SIGILL) 69 signame = "SIGILL"; 70 else 71 signame = "unexpected signal"; 72 73 printf("[INFO]\t%s: FLAGS = 0x%lx, CS = 0x%hx\n", signame, 74 (unsigned long)ctx->uc_mcontext.gregs[REG_EFL], 75 (unsigned short)ctx->uc_mcontext.gregs[REG_CS]); 76 77 got_signal = 1; 78} 79 80asm ( 81 ".pushsection .rodata\n\t" 82 ".type vmcode_bound, @object\n\t" 83 "vmcode:\n\t" 84 "vmcode_bound:\n\t" 85 ".code16\n\t" 86 "bound %ax, (2048)\n\t" 87 "int3\n\t" 88 "vmcode_sysenter:\n\t" 89 "sysenter\n\t" 90 "vmcode_syscall:\n\t" 91 "syscall\n\t" 92 "vmcode_sti:\n\t" 93 "sti\n\t" 94 "vmcode_int3:\n\t" 95 "int3\n\t" 96 "vmcode_int80:\n\t" 97 "int $0x80\n\t" 98 ".size vmcode, . - vmcode\n\t" 99 "end_vmcode:\n\t" 100 ".code32\n\t" 101 ".popsection" 102 ); 103 104extern unsigned char vmcode[], end_vmcode[]; 105extern unsigned char vmcode_bound[], vmcode_sysenter[], vmcode_syscall[], 106 vmcode_sti[], vmcode_int3[], vmcode_int80[]; 107 108/* Returns false if the test was skipped. */ 109static bool do_test(struct vm86plus_struct *v86, unsigned long eip, 110 unsigned int rettype, unsigned int retarg, 111 const char *text) 112{ 113 long ret; 114 115 printf("[RUN]\t%s from vm86 mode\n", text); 116 v86->regs.eip = eip; 117 ret = vm86(VM86_ENTER, v86); 118 119 if (ret == -1 && (errno == ENOSYS || errno == EPERM)) { 120 printf("[SKIP]\tvm86 %s\n", 121 errno == ENOSYS ? "not supported" : "not allowed"); 122 return false; 123 } 124 125 if (VM86_TYPE(ret) == VM86_INTx) { 126 char trapname[32]; 127 int trapno = VM86_ARG(ret); 128 if (trapno == 13) 129 strcpy(trapname, "GP"); 130 else if (trapno == 5) 131 strcpy(trapname, "BR"); 132 else if (trapno == 14) 133 strcpy(trapname, "PF"); 134 else 135 sprintf(trapname, "%d", trapno); 136 137 printf("[INFO]\tExited vm86 mode due to #%s\n", trapname); 138 } else if (VM86_TYPE(ret) == VM86_UNKNOWN) { 139 printf("[INFO]\tExited vm86 mode due to unhandled GP fault\n"); 140 } else if (VM86_TYPE(ret) == VM86_TRAP) { 141 printf("[INFO]\tExited vm86 mode due to a trap (arg=%ld)\n", 142 VM86_ARG(ret)); 143 } else if (VM86_TYPE(ret) == VM86_SIGNAL) { 144 printf("[INFO]\tExited vm86 mode due to a signal\n"); 145 } else if (VM86_TYPE(ret) == VM86_STI) { 146 printf("[INFO]\tExited vm86 mode due to STI\n"); 147 } else { 148 printf("[INFO]\tExited vm86 mode due to type %ld, arg %ld\n", 149 VM86_TYPE(ret), VM86_ARG(ret)); 150 } 151 152 if (rettype == -1 || 153 (VM86_TYPE(ret) == rettype && VM86_ARG(ret) == retarg)) { 154 printf("[OK]\tReturned correctly\n"); 155 } else { 156 printf("[FAIL]\tIncorrect return reason\n"); 157 nerrs++; 158 } 159 160 return true; 161} 162 163int main(void) 164{ 165 struct vm86plus_struct v86; 166 unsigned char *addr = mmap((void *)load_addr, 4096, 167 PROT_READ | PROT_WRITE | PROT_EXEC, 168 MAP_ANONYMOUS | MAP_PRIVATE, -1,0); 169 if (addr != (unsigned char *)load_addr) 170 err(1, "mmap"); 171 172 memcpy(addr, vmcode, end_vmcode - vmcode); 173 addr[2048] = 2; 174 addr[2050] = 3; 175 176 memset(&v86, 0, sizeof(v86)); 177 178 v86.regs.cs = load_addr / 16; 179 v86.regs.ss = load_addr / 16; 180 v86.regs.ds = load_addr / 16; 181 v86.regs.es = load_addr / 16; 182 183 assert((v86.regs.cs & 3) == 0); /* Looks like RPL = 0 */ 184 185 /* #BR -- should deliver SIG??? */ 186 do_test(&v86, vmcode_bound - vmcode, VM86_INTx, 5, "#BR"); 187 188 /* 189 * SYSENTER -- should cause #GP or #UD depending on CPU. 190 * Expected return type -1 means that we shouldn't validate 191 * the vm86 return value. This will avoid problems on non-SEP 192 * CPUs. 193 */ 194 sethandler(SIGILL, sighandler, 0); 195 do_test(&v86, vmcode_sysenter - vmcode, -1, 0, "SYSENTER"); 196 clearhandler(SIGILL); 197 198 /* 199 * SYSCALL would be a disaster in VM86 mode. Fortunately, 200 * there is no kernel that both enables SYSCALL and sets 201 * EFER.SCE, so it's #UD on all systems. But vm86 is 202 * buggy (or has a "feature"), so the SIGILL will actually 203 * be delivered. 204 */ 205 sethandler(SIGILL, sighandler, 0); 206 do_test(&v86, vmcode_syscall - vmcode, VM86_SIGNAL, 0, "SYSCALL"); 207 clearhandler(SIGILL); 208 209 /* STI with VIP set */ 210 v86.regs.eflags |= X86_EFLAGS_VIP; 211 v86.regs.eflags &= ~X86_EFLAGS_IF; 212 do_test(&v86, vmcode_sti - vmcode, VM86_STI, 0, "STI with VIP set"); 213 214 /* INT3 -- should cause #BP */ 215 do_test(&v86, vmcode_int3 - vmcode, VM86_TRAP, 3, "INT3"); 216 217 /* INT80 -- should exit with "INTx 0x80" */ 218 v86.regs.eax = (unsigned int)-1; 219 do_test(&v86, vmcode_int80 - vmcode, VM86_INTx, 0x80, "int80"); 220 221 /* Execute a null pointer */ 222 v86.regs.cs = 0; 223 v86.regs.ss = 0; 224 sethandler(SIGSEGV, sighandler, 0); 225 got_signal = 0; 226 if (do_test(&v86, 0, VM86_SIGNAL, 0, "Execute null pointer") && 227 !got_signal) { 228 printf("[FAIL]\tDid not receive SIGSEGV\n"); 229 nerrs++; 230 } 231 clearhandler(SIGSEGV); 232 233 /* Make sure nothing explodes if we fork. */ 234 if (fork() > 0) 235 return 0; 236 237 return (nerrs == 0 ? 0 : 1); 238} 239