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