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 28 static unsigned long load_addr = 0x10000; 29 static int nerrs = 0; 30 31 static 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 43 static 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 53 static sig_atomic_t got_signal; 54 55 static 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 80 asm ( 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 ); 103 104 extern unsigned char vmcode[], end_vmcode[]; 105 extern unsigned char vmcode_bound[], vmcode_sysenter[], vmcode_syscall[], 106 vmcode_sti[], vmcode_int3[], vmcode_int80[]; 107 108 /* Returns false if the test was skipped. */ 109 static 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) { 120 printf("[SKIP]\tvm86 not supported\n"); 121 return false; 122 } 123 124 if (VM86_TYPE(ret) == VM86_INTx) { 125 char trapname[32]; 126 int trapno = VM86_ARG(ret); 127 if (trapno == 13) 128 strcpy(trapname, "GP"); 129 else if (trapno == 5) 130 strcpy(trapname, "BR"); 131 else if (trapno == 14) 132 strcpy(trapname, "PF"); 133 else 134 sprintf(trapname, "%d", trapno); 135 136 printf("[INFO]\tExited vm86 mode due to #%s\n", trapname); 137 } else if (VM86_TYPE(ret) == VM86_UNKNOWN) { 138 printf("[INFO]\tExited vm86 mode due to unhandled GP fault\n"); 139 } else if (VM86_TYPE(ret) == VM86_TRAP) { 140 printf("[INFO]\tExited vm86 mode due to a trap (arg=%ld)\n", 141 VM86_ARG(ret)); 142 } else if (VM86_TYPE(ret) == VM86_SIGNAL) { 143 printf("[INFO]\tExited vm86 mode due to a signal\n"); 144 } else if (VM86_TYPE(ret) == VM86_STI) { 145 printf("[INFO]\tExited vm86 mode due to STI\n"); 146 } else { 147 printf("[INFO]\tExited vm86 mode due to type %ld, arg %ld\n", 148 VM86_TYPE(ret), VM86_ARG(ret)); 149 } 150 151 if (rettype == -1 || 152 (VM86_TYPE(ret) == rettype && VM86_ARG(ret) == retarg)) { 153 printf("[OK]\tReturned correctly\n"); 154 } else { 155 printf("[FAIL]\tIncorrect return reason\n"); 156 nerrs++; 157 } 158 159 return true; 160 } 161 162 int main(void) 163 { 164 struct vm86plus_struct v86; 165 unsigned char *addr = mmap((void *)load_addr, 4096, 166 PROT_READ | PROT_WRITE | PROT_EXEC, 167 MAP_ANONYMOUS | MAP_PRIVATE, -1,0); 168 if (addr != (unsigned char *)load_addr) 169 err(1, "mmap"); 170 171 memcpy(addr, vmcode, end_vmcode - vmcode); 172 addr[2048] = 2; 173 addr[2050] = 3; 174 175 memset(&v86, 0, sizeof(v86)); 176 177 v86.regs.cs = load_addr / 16; 178 v86.regs.ss = load_addr / 16; 179 v86.regs.ds = load_addr / 16; 180 v86.regs.es = load_addr / 16; 181 182 assert((v86.regs.cs & 3) == 0); /* Looks like RPL = 0 */ 183 184 /* #BR -- should deliver SIG??? */ 185 do_test(&v86, vmcode_bound - vmcode, VM86_INTx, 5, "#BR"); 186 187 /* 188 * SYSENTER -- should cause #GP or #UD depending on CPU. 189 * Expected return type -1 means that we shouldn't validate 190 * the vm86 return value. This will avoid problems on non-SEP 191 * CPUs. 192 */ 193 sethandler(SIGILL, sighandler, 0); 194 do_test(&v86, vmcode_sysenter - vmcode, -1, 0, "SYSENTER"); 195 clearhandler(SIGILL); 196 197 /* 198 * SYSCALL would be a disaster in VM86 mode. Fortunately, 199 * there is no kernel that both enables SYSCALL and sets 200 * EFER.SCE, so it's #UD on all systems. But vm86 is 201 * buggy (or has a "feature"), so the SIGILL will actually 202 * be delivered. 203 */ 204 sethandler(SIGILL, sighandler, 0); 205 do_test(&v86, vmcode_syscall - vmcode, VM86_SIGNAL, 0, "SYSCALL"); 206 clearhandler(SIGILL); 207 208 /* STI with VIP set */ 209 v86.regs.eflags |= X86_EFLAGS_VIP; 210 v86.regs.eflags &= ~X86_EFLAGS_IF; 211 do_test(&v86, vmcode_sti - vmcode, VM86_STI, 0, "STI with VIP set"); 212 213 /* INT3 -- should cause #BP */ 214 do_test(&v86, vmcode_int3 - vmcode, VM86_TRAP, 3, "INT3"); 215 216 /* INT80 -- should exit with "INTx 0x80" */ 217 v86.regs.eax = (unsigned int)-1; 218 do_test(&v86, vmcode_int80 - vmcode, VM86_INTx, 0x80, "int80"); 219 220 /* Execute a null pointer */ 221 v86.regs.cs = 0; 222 v86.regs.ss = 0; 223 sethandler(SIGSEGV, sighandler, 0); 224 got_signal = 0; 225 if (do_test(&v86, 0, VM86_SIGNAL, 0, "Execute null pointer") && 226 !got_signal) { 227 printf("[FAIL]\tDid not receive SIGSEGV\n"); 228 nerrs++; 229 } 230 clearhandler(SIGSEGV); 231 232 return (nerrs == 0 ? 0 : 1); 233 } 234