1 // SPDX-License-Identifier: GPL-2.0-only 2 /* 3 * entry_from_vm86.c - tests kernel entries from vm86 mode 4 * Copyright (c) 2014-2015 Andrew Lutomirski 5 * 6 * This exercises a few paths that need to special-case vm86 mode. 7 */ 8 9 #define _GNU_SOURCE 10 11 #include <assert.h> 12 #include <stdlib.h> 13 #include <sys/syscall.h> 14 #include <sys/signal.h> 15 #include <sys/ucontext.h> 16 #include <unistd.h> 17 #include <stdio.h> 18 #include <string.h> 19 #include <inttypes.h> 20 #include <sys/mman.h> 21 #include <err.h> 22 #include <stddef.h> 23 #include <stdbool.h> 24 #include <errno.h> 25 #include <sys/vm86.h> 26 27 static unsigned long load_addr = 0x10000; 28 static int nerrs = 0; 29 30 static void sethandler(int sig, void (*handler)(int, siginfo_t *, void *), 31 int flags) 32 { 33 struct sigaction sa; 34 memset(&sa, 0, sizeof(sa)); 35 sa.sa_sigaction = handler; 36 sa.sa_flags = SA_SIGINFO | flags; 37 sigemptyset(&sa.sa_mask); 38 if (sigaction(sig, &sa, 0)) 39 err(1, "sigaction"); 40 } 41 42 static void clearhandler(int sig) 43 { 44 struct sigaction sa; 45 memset(&sa, 0, sizeof(sa)); 46 sa.sa_handler = SIG_DFL; 47 sigemptyset(&sa.sa_mask); 48 if (sigaction(sig, &sa, 0)) 49 err(1, "sigaction"); 50 } 51 52 static sig_atomic_t got_signal; 53 54 static void sighandler(int sig, siginfo_t *info, void *ctx_void) 55 { 56 ucontext_t *ctx = (ucontext_t*)ctx_void; 57 58 if (ctx->uc_mcontext.gregs[REG_EFL] & X86_EFLAGS_VM || 59 (ctx->uc_mcontext.gregs[REG_CS] & 3) != 3) { 60 printf("[FAIL]\tSignal frame should not reflect vm86 mode\n"); 61 nerrs++; 62 } 63 64 const char *signame; 65 if (sig == SIGSEGV) 66 signame = "SIGSEGV"; 67 else if (sig == SIGILL) 68 signame = "SIGILL"; 69 else 70 signame = "unexpected signal"; 71 72 printf("[INFO]\t%s: FLAGS = 0x%lx, CS = 0x%hx\n", signame, 73 (unsigned long)ctx->uc_mcontext.gregs[REG_EFL], 74 (unsigned short)ctx->uc_mcontext.gregs[REG_CS]); 75 76 got_signal = 1; 77 } 78 79 asm ( 80 ".pushsection .rodata\n\t" 81 ".type vmcode_bound, @object\n\t" 82 "vmcode:\n\t" 83 "vmcode_bound:\n\t" 84 ".code16\n\t" 85 "bound %ax, (2048)\n\t" 86 "int3\n\t" 87 "vmcode_sysenter:\n\t" 88 "sysenter\n\t" 89 "vmcode_syscall:\n\t" 90 "syscall\n\t" 91 "vmcode_sti:\n\t" 92 "sti\n\t" 93 "vmcode_int3:\n\t" 94 "int3\n\t" 95 "vmcode_int80:\n\t" 96 "int $0x80\n\t" 97 "vmcode_popf_hlt:\n\t" 98 "push %ax\n\t" 99 "popf\n\t" 100 "hlt\n\t" 101 "vmcode_umip:\n\t" 102 /* addressing via displacements */ 103 "smsw (2052)\n\t" 104 "sidt (2054)\n\t" 105 "sgdt (2060)\n\t" 106 /* addressing via registers */ 107 "mov $2066, %bx\n\t" 108 "smsw (%bx)\n\t" 109 "mov $2068, %bx\n\t" 110 "sidt (%bx)\n\t" 111 "mov $2074, %bx\n\t" 112 "sgdt (%bx)\n\t" 113 /* register operands, only for smsw */ 114 "smsw %ax\n\t" 115 "mov %ax, (2080)\n\t" 116 "int3\n\t" 117 "vmcode_umip_str:\n\t" 118 "str %eax\n\t" 119 "vmcode_umip_sldt:\n\t" 120 "sldt %eax\n\t" 121 "int3\n\t" 122 ".size vmcode, . - vmcode\n\t" 123 "end_vmcode:\n\t" 124 ".code32\n\t" 125 ".popsection" 126 ); 127 128 extern unsigned char vmcode[], end_vmcode[]; 129 extern unsigned char vmcode_bound[], vmcode_sysenter[], vmcode_syscall[], 130 vmcode_sti[], vmcode_int3[], vmcode_int80[], vmcode_popf_hlt[], 131 vmcode_umip[], vmcode_umip_str[], vmcode_umip_sldt[]; 132 133 /* Returns false if the test was skipped. */ 134 static bool do_test(struct vm86plus_struct *v86, unsigned long eip, 135 unsigned int rettype, unsigned int retarg, 136 const char *text) 137 { 138 long ret; 139 140 printf("[RUN]\t%s from vm86 mode\n", text); 141 v86->regs.eip = eip; 142 ret = vm86(VM86_ENTER, v86); 143 144 if (ret == -1 && (errno == ENOSYS || errno == EPERM)) { 145 printf("[SKIP]\tvm86 %s\n", 146 errno == ENOSYS ? "not supported" : "not allowed"); 147 return false; 148 } 149 150 if (VM86_TYPE(ret) == VM86_INTx) { 151 char trapname[32]; 152 int trapno = VM86_ARG(ret); 153 if (trapno == 13) 154 strcpy(trapname, "GP"); 155 else if (trapno == 5) 156 strcpy(trapname, "BR"); 157 else if (trapno == 14) 158 strcpy(trapname, "PF"); 159 else 160 sprintf(trapname, "%d", trapno); 161 162 printf("[INFO]\tExited vm86 mode due to #%s\n", trapname); 163 } else if (VM86_TYPE(ret) == VM86_UNKNOWN) { 164 printf("[INFO]\tExited vm86 mode due to unhandled GP fault\n"); 165 } else if (VM86_TYPE(ret) == VM86_TRAP) { 166 printf("[INFO]\tExited vm86 mode due to a trap (arg=%ld)\n", 167 VM86_ARG(ret)); 168 } else if (VM86_TYPE(ret) == VM86_SIGNAL) { 169 printf("[INFO]\tExited vm86 mode due to a signal\n"); 170 } else if (VM86_TYPE(ret) == VM86_STI) { 171 printf("[INFO]\tExited vm86 mode due to STI\n"); 172 } else { 173 printf("[INFO]\tExited vm86 mode due to type %ld, arg %ld\n", 174 VM86_TYPE(ret), VM86_ARG(ret)); 175 } 176 177 if (rettype == -1 || 178 (VM86_TYPE(ret) == rettype && VM86_ARG(ret) == retarg)) { 179 printf("[OK]\tReturned correctly\n"); 180 } else { 181 printf("[FAIL]\tIncorrect return reason (started at eip = 0x%lx, ended at eip = 0x%lx)\n", eip, v86->regs.eip); 182 nerrs++; 183 } 184 185 return true; 186 } 187 188 void do_umip_tests(struct vm86plus_struct *vm86, unsigned char *test_mem) 189 { 190 struct table_desc { 191 unsigned short limit; 192 unsigned long base; 193 } __attribute__((packed)); 194 195 /* Initialize variables with arbitrary values */ 196 struct table_desc gdt1 = { .base = 0x3c3c3c3c, .limit = 0x9999 }; 197 struct table_desc gdt2 = { .base = 0x1a1a1a1a, .limit = 0xaeae }; 198 struct table_desc idt1 = { .base = 0x7b7b7b7b, .limit = 0xf1f1 }; 199 struct table_desc idt2 = { .base = 0x89898989, .limit = 0x1313 }; 200 unsigned short msw1 = 0x1414, msw2 = 0x2525, msw3 = 3737; 201 202 /* UMIP -- exit with INT3 unless kernel emulation did not trap #GP */ 203 do_test(vm86, vmcode_umip - vmcode, VM86_TRAP, 3, "UMIP tests"); 204 205 /* Results from displacement-only addressing */ 206 msw1 = *(unsigned short *)(test_mem + 2052); 207 memcpy(&idt1, test_mem + 2054, sizeof(idt1)); 208 memcpy(&gdt1, test_mem + 2060, sizeof(gdt1)); 209 210 /* Results from register-indirect addressing */ 211 msw2 = *(unsigned short *)(test_mem + 2066); 212 memcpy(&idt2, test_mem + 2068, sizeof(idt2)); 213 memcpy(&gdt2, test_mem + 2074, sizeof(gdt2)); 214 215 /* Results when using register operands */ 216 msw3 = *(unsigned short *)(test_mem + 2080); 217 218 printf("[INFO]\tResult from SMSW:[0x%04x]\n", msw1); 219 printf("[INFO]\tResult from SIDT: limit[0x%04x]base[0x%08lx]\n", 220 idt1.limit, idt1.base); 221 printf("[INFO]\tResult from SGDT: limit[0x%04x]base[0x%08lx]\n", 222 gdt1.limit, gdt1.base); 223 224 if (msw1 != msw2 || msw1 != msw3) 225 printf("[FAIL]\tAll the results of SMSW should be the same.\n"); 226 else 227 printf("[PASS]\tAll the results from SMSW are identical.\n"); 228 229 if (memcmp(&gdt1, &gdt2, sizeof(gdt1))) 230 printf("[FAIL]\tAll the results of SGDT should be the same.\n"); 231 else 232 printf("[PASS]\tAll the results from SGDT are identical.\n"); 233 234 if (memcmp(&idt1, &idt2, sizeof(idt1))) 235 printf("[FAIL]\tAll the results of SIDT should be the same.\n"); 236 else 237 printf("[PASS]\tAll the results from SIDT are identical.\n"); 238 239 sethandler(SIGILL, sighandler, 0); 240 do_test(vm86, vmcode_umip_str - vmcode, VM86_SIGNAL, 0, 241 "STR instruction"); 242 clearhandler(SIGILL); 243 244 sethandler(SIGILL, sighandler, 0); 245 do_test(vm86, vmcode_umip_sldt - vmcode, VM86_SIGNAL, 0, 246 "SLDT instruction"); 247 clearhandler(SIGILL); 248 } 249 250 int main(void) 251 { 252 struct vm86plus_struct v86; 253 unsigned char *addr = mmap((void *)load_addr, 4096, 254 PROT_READ | PROT_WRITE | PROT_EXEC, 255 MAP_ANONYMOUS | MAP_PRIVATE, -1,0); 256 if (addr != (unsigned char *)load_addr) 257 err(1, "mmap"); 258 259 memcpy(addr, vmcode, end_vmcode - vmcode); 260 addr[2048] = 2; 261 addr[2050] = 3; 262 263 memset(&v86, 0, sizeof(v86)); 264 265 v86.regs.cs = load_addr / 16; 266 v86.regs.ss = load_addr / 16; 267 v86.regs.ds = load_addr / 16; 268 v86.regs.es = load_addr / 16; 269 270 /* Use the end of the page as our stack. */ 271 v86.regs.esp = 4096; 272 273 assert((v86.regs.cs & 3) == 0); /* Looks like RPL = 0 */ 274 275 /* #BR -- should deliver SIG??? */ 276 do_test(&v86, vmcode_bound - vmcode, VM86_INTx, 5, "#BR"); 277 278 /* 279 * SYSENTER -- should cause #GP or #UD depending on CPU. 280 * Expected return type -1 means that we shouldn't validate 281 * the vm86 return value. This will avoid problems on non-SEP 282 * CPUs. 283 */ 284 sethandler(SIGILL, sighandler, 0); 285 do_test(&v86, vmcode_sysenter - vmcode, -1, 0, "SYSENTER"); 286 clearhandler(SIGILL); 287 288 /* 289 * SYSCALL would be a disaster in VM86 mode. Fortunately, 290 * there is no kernel that both enables SYSCALL and sets 291 * EFER.SCE, so it's #UD on all systems. But vm86 is 292 * buggy (or has a "feature"), so the SIGILL will actually 293 * be delivered. 294 */ 295 sethandler(SIGILL, sighandler, 0); 296 do_test(&v86, vmcode_syscall - vmcode, VM86_SIGNAL, 0, "SYSCALL"); 297 clearhandler(SIGILL); 298 299 /* STI with VIP set */ 300 v86.regs.eflags |= X86_EFLAGS_VIP; 301 v86.regs.eflags &= ~X86_EFLAGS_IF; 302 do_test(&v86, vmcode_sti - vmcode, VM86_STI, 0, "STI with VIP set"); 303 304 /* POPF with VIP set but IF clear: should not trap */ 305 v86.regs.eflags = X86_EFLAGS_VIP; 306 v86.regs.eax = 0; 307 do_test(&v86, vmcode_popf_hlt - vmcode, VM86_UNKNOWN, 0, "POPF with VIP set and IF clear"); 308 309 /* POPF with VIP set and IF set: should trap */ 310 v86.regs.eflags = X86_EFLAGS_VIP; 311 v86.regs.eax = X86_EFLAGS_IF; 312 do_test(&v86, vmcode_popf_hlt - vmcode, VM86_STI, 0, "POPF with VIP and IF set"); 313 314 /* POPF with VIP clear and IF set: should not trap */ 315 v86.regs.eflags = 0; 316 v86.regs.eax = X86_EFLAGS_IF; 317 do_test(&v86, vmcode_popf_hlt - vmcode, VM86_UNKNOWN, 0, "POPF with VIP clear and IF set"); 318 319 v86.regs.eflags = 0; 320 321 /* INT3 -- should cause #BP */ 322 do_test(&v86, vmcode_int3 - vmcode, VM86_TRAP, 3, "INT3"); 323 324 /* INT80 -- should exit with "INTx 0x80" */ 325 v86.regs.eax = (unsigned int)-1; 326 do_test(&v86, vmcode_int80 - vmcode, VM86_INTx, 0x80, "int80"); 327 328 /* UMIP -- should exit with INTx 0x80 unless UMIP was not disabled */ 329 do_umip_tests(&v86, addr); 330 331 /* Execute a null pointer */ 332 v86.regs.cs = 0; 333 v86.regs.ss = 0; 334 sethandler(SIGSEGV, sighandler, 0); 335 got_signal = 0; 336 if (do_test(&v86, 0, VM86_SIGNAL, 0, "Execute null pointer") && 337 !got_signal) { 338 printf("[FAIL]\tDid not receive SIGSEGV\n"); 339 nerrs++; 340 } 341 clearhandler(SIGSEGV); 342 343 /* Make sure nothing explodes if we fork. */ 344 if (fork() == 0) 345 return 0; 346 347 return (nerrs == 0 ? 0 : 1); 348 } 349