entry_from_vm86.c 9.5 KB

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