tools/testing/selftests/x86/entry_from_vm86.c

   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         "vmcode_umip:\n\t"
  99         /* addressing via displacements */
 100         "smsw (2052)\n\t"
 101         "sidt (2054)\n\t"
 102         "sgdt (2060)\n\t"
 103         /* addressing via registers */
 104         "mov $2066, %bx\n\t"
 105         "smsw (%bx)\n\t"
 106         "mov $2068, %bx\n\t"
 107         "sidt (%bx)\n\t"
 108         "mov $2074, %bx\n\t"
 109         "sgdt (%bx)\n\t"
 110         /* register operands, only for smsw */
 111         "smsw %ax\n\t"
 112         "mov %ax, (2080)\n\t"
 113         "int3\n\t"
 114         "vmcode_umip_str:\n\t"
 115         "str %eax\n\t"
 116         "vmcode_umip_sldt:\n\t"
 117         "sldt %eax\n\t"
 118         "int3\n\t"
 119         ".size vmcode, . - vmcode\n\t"
 120         "end_vmcode:\n\t"
 121         ".code32\n\t"
 122         ".popsection"
 123         );
 124
 125 extern unsigned char vmcode[], end_vmcode[];
 126 extern unsigned char vmcode_bound[], vmcode_sysenter[], vmcode_syscall[],
 127         vmcode_sti[], vmcode_int3[], vmcode_int80[], vmcode_umip[],
 128         vmcode_umip_str[], vmcode_umip_sldt[];
 129
 130 /* Returns false if the test was skipped. */
 131 static bool do_test(struct vm86plus_struct *v86, unsigned long eip,
 132                     unsigned int rettype, unsigned int retarg,
 133                     const char *text)
 134 {
 135         long ret;
 136
 137         printf("[RUN]\t%s from vm86 mode\n", text);
 138         v86->regs.eip = eip;
 139         ret = vm86(VM86_ENTER, v86);
 140
 141         if (ret == -1 && (errno == ENOSYS || errno == EPERM)) {
 142                 printf("[SKIP]\tvm86 %s\n",
 143                        errno == ENOSYS ? "not supported" : "not allowed");
 144                 return false;
 145         }
 146
 147         if (VM86_TYPE(ret) == VM86_INTx) {
 148                 char trapname[32];
 149                 int trapno = VM86_ARG(ret);
 150                 if (trapno == 13)
 151                         strcpy(trapname, "GP");
 152                 else if (trapno == 5)
 153                         strcpy(trapname, "BR");
 154                 else if (trapno == 14)
 155                         strcpy(trapname, "PF");
 156                 else
 157                         sprintf(trapname, "%d", trapno);
 158
 159                 printf("[INFO]\tExited vm86 mode due to #%s\n", trapname);
 160         } else if (VM86_TYPE(ret) == VM86_UNKNOWN) {
 161                 printf("[INFO]\tExited vm86 mode due to unhandled GP fault\n");
 162         } else if (VM86_TYPE(ret) == VM86_TRAP) {
 163                 printf("[INFO]\tExited vm86 mode due to a trap (arg=%ld)\n",
 164                        VM86_ARG(ret));
 165         } else if (VM86_TYPE(ret) == VM86_SIGNAL) {
 166                 printf("[INFO]\tExited vm86 mode due to a signal\n");
 167         } else if (VM86_TYPE(ret) == VM86_STI) {
 168                 printf("[INFO]\tExited vm86 mode due to STI\n");
 169         } else {
 170                 printf("[INFO]\tExited vm86 mode due to type %ld, arg %ld\n",
 171                        VM86_TYPE(ret), VM86_ARG(ret));
 172         }
 173
 174         if (rettype == -1 ||
 175             (VM86_TYPE(ret) == rettype && VM86_ARG(ret) == retarg)) {
 176                 printf("[OK]\tReturned correctly\n");
 177         } else {
 178                 printf("[FAIL]\tIncorrect return reason\n");
 179                 nerrs++;
 180         }
 181
 182         return true;
 183 }
 184
 185 void do_umip_tests(struct vm86plus_struct *vm86, unsigned char *test_mem)
 186 {
 187         struct table_desc {
 188                 unsigned short limit;
 189                 unsigned long base;
 190         } __attribute__((packed));
 191
 192         /* Initialize variables with arbitrary values */
 193         struct table_desc gdt1 = { .base = 0x3c3c3c3c, .limit = 0x9999 };
 194         struct table_desc gdt2 = { .base = 0x1a1a1a1a, .limit = 0xaeae };
 195         struct table_desc idt1 = { .base = 0x7b7b7b7b, .limit = 0xf1f1 };
 196         struct table_desc idt2 = { .base = 0x89898989, .limit = 0x1313 };
 197         unsigned short msw1 = 0x1414, msw2 = 0x2525, msw3 = 3737;
 198
 199         /* UMIP -- exit with INT3 unless kernel emulation did not trap #GP */
 200         do_test(vm86, vmcode_umip - vmcode, VM86_TRAP, 3, "UMIP tests");
 201
 202         /* Results from displacement-only addressing */
 203         msw1 = *(unsigned short *)(test_mem + 2052);
 204         memcpy(&idt1, test_mem + 2054, sizeof(idt1));
 205         memcpy(&gdt1, test_mem + 2060, sizeof(gdt1));
 206
 207         /* Results from register-indirect addressing */
 208         msw2 = *(unsigned short *)(test_mem + 2066);
 209         memcpy(&idt2, test_mem + 2068, sizeof(idt2));
 210         memcpy(&gdt2, test_mem + 2074, sizeof(gdt2));
 211
 212         /* Results when using register operands */
 213         msw3 = *(unsigned short *)(test_mem + 2080);
 214
 215         printf("[INFO]\tResult from SMSW:[0x%04x]\n", msw1);
 216         printf("[INFO]\tResult from SIDT: limit[0x%04x]base[0x%08lx]\n",
 217                idt1.limit, idt1.base);
 218         printf("[INFO]\tResult from SGDT: limit[0x%04x]base[0x%08lx]\n",
 219                gdt1.limit, gdt1.base);
 220
 221         if (msw1 != msw2 || msw1 != msw3)
 222                 printf("[FAIL]\tAll the results of SMSW should be the same.\n");
 223         else
 224                 printf("[PASS]\tAll the results from SMSW are identical.\n");
 225
 226         if (memcmp(&gdt1, &gdt2, sizeof(gdt1)))
 227                 printf("[FAIL]\tAll the results of SGDT should be the same.\n");
 228         else
 229                 printf("[PASS]\tAll the results from SGDT are identical.\n");
 230
 231         if (memcmp(&idt1, &idt2, sizeof(idt1)))
 232                 printf("[FAIL]\tAll the results of SIDT should be the same.\n");
 233         else
 234                 printf("[PASS]\tAll the results from SIDT are identical.\n");
 235
 236         sethandler(SIGILL, sighandler, 0);
 237         do_test(vm86, vmcode_umip_str - vmcode, VM86_SIGNAL, 0,
 238                 "STR instruction");
 239         clearhandler(SIGILL);
 240
 241         sethandler(SIGILL, sighandler, 0);
 242         do_test(vm86, vmcode_umip_sldt - vmcode, VM86_SIGNAL, 0,
 243                 "SLDT instruction");
 244         clearhandler(SIGILL);
 245 }
 246
 247 int main(void)
 248 {
 249         struct vm86plus_struct v86;
 250         unsigned char *addr = mmap((void *)load_addr, 4096,
 251                                    PROT_READ | PROT_WRITE | PROT_EXEC,
 252                                    MAP_ANONYMOUS | MAP_PRIVATE, -1,0);
 253         if (addr != (unsigned char *)load_addr)
 254                 err(1, "mmap");
 255
 256         memcpy(addr, vmcode, end_vmcode - vmcode);
 257         addr[2048] = 2;
 258         addr[2050] = 3;
 259
 260         memset(&v86, 0, sizeof(v86));
 261
 262         v86.regs.cs = load_addr / 16;
 263         v86.regs.ss = load_addr / 16;
 264         v86.regs.ds = load_addr / 16;
 265         v86.regs.es = load_addr / 16;
 266
 267         assert((v86.regs.cs & 3) == 0); /* Looks like RPL = 0 */
 268
 269         /* #BR -- should deliver SIG??? */
 270         do_test(&v86, vmcode_bound - vmcode, VM86_INTx, 5, "#BR");
 271
 272         /*
 273          * SYSENTER -- should cause #GP or #UD depending on CPU.
 274          * Expected return type -1 means that we shouldn't validate
 275          * the vm86 return value.  This will avoid problems on non-SEP
 276          * CPUs.
 277          */
 278         sethandler(SIGILL, sighandler, 0);
 279         do_test(&v86, vmcode_sysenter - vmcode, -1, 0, "SYSENTER");
 280         clearhandler(SIGILL);
 281
 282         /*
 283          * SYSCALL would be a disaster in VM86 mode.  Fortunately,
 284          * there is no kernel that both enables SYSCALL and sets
 285          * EFER.SCE, so it's #UD on all systems.  But vm86 is
 286          * buggy (or has a "feature"), so the SIGILL will actually
 287          * be delivered.
 288          */
 289         sethandler(SIGILL, sighandler, 0);
 290         do_test(&v86, vmcode_syscall - vmcode, VM86_SIGNAL, 0, "SYSCALL");
 291         clearhandler(SIGILL);
 292
 293         /* STI with VIP set */
 294         v86.regs.eflags |= X86_EFLAGS_VIP;
 295         v86.regs.eflags &= ~X86_EFLAGS_IF;
 296         do_test(&v86, vmcode_sti - vmcode, VM86_STI, 0, "STI with VIP set");
 297
 298         /* INT3 -- should cause #BP */
 299         do_test(&v86, vmcode_int3 - vmcode, VM86_TRAP, 3, "INT3");
 300
 301         /* INT80 -- should exit with "INTx 0x80" */
 302         v86.regs.eax = (unsigned int)-1;
 303         do_test(&v86, vmcode_int80 - vmcode, VM86_INTx, 0x80, "int80");
 304
 305         /* UMIP -- should exit with INTx 0x80 unless UMIP was not disabled */
 306         do_umip_tests(&v86, addr);
 307
 308         /* Execute a null pointer */
 309         v86.regs.cs = 0;
 310         v86.regs.ss = 0;
 311         sethandler(SIGSEGV, sighandler, 0);
 312         got_signal = 0;
 313         if (do_test(&v86, 0, VM86_SIGNAL, 0, "Execute null pointer") &&
 314             !got_signal) {
 315                 printf("[FAIL]\tDid not receive SIGSEGV\n");
 316                 nerrs++;
 317         }
 318         clearhandler(SIGSEGV);
 319
 320         /* Make sure nothing explodes if we fork. */
 321         if (fork() > 0)
 322                 return 0;
 323
 324         return (nerrs == 0 ? 0 : 1);
 325 }