tools/testing/selftests/x86/entry_from_vm86.c

   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 }