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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 
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 
sethandler(int sig,void (* handler)(int,siginfo_t *,void *),int flags)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 
clearhandler(int sig)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 
sighandler(int sig,siginfo_t * info,void * ctx_void)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_popf_hlt:\n\t"
99 	"push %ax\n\t"
100 	"popf\n\t"
101 	"hlt\n\t"
102 	"vmcode_umip:\n\t"
103 	/* addressing via displacements */
104 	"smsw (2052)\n\t"
105 	"sidt (2054)\n\t"
106 	"sgdt (2060)\n\t"
107 	/* addressing via registers */
108 	"mov $2066, %bx\n\t"
109 	"smsw (%bx)\n\t"
110 	"mov $2068, %bx\n\t"
111 	"sidt (%bx)\n\t"
112 	"mov $2074, %bx\n\t"
113 	"sgdt (%bx)\n\t"
114 	/* register operands, only for smsw */
115 	"smsw %ax\n\t"
116 	"mov %ax, (2080)\n\t"
117 	"int3\n\t"
118 	"vmcode_umip_str:\n\t"
119 	"str %eax\n\t"
120 	"vmcode_umip_sldt:\n\t"
121 	"sldt %eax\n\t"
122 	"int3\n\t"
123 	".size vmcode, . - vmcode\n\t"
124 	"end_vmcode:\n\t"
125 	".code32\n\t"
126 	".popsection"
127 	);
128 
129 extern unsigned char vmcode[], end_vmcode[];
130 extern unsigned char vmcode_bound[], vmcode_sysenter[], vmcode_syscall[],
131 	vmcode_sti[], vmcode_int3[], vmcode_int80[], vmcode_popf_hlt[],
132 	vmcode_umip[], vmcode_umip_str[], vmcode_umip_sldt[];
133 
134 /* 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)135 static bool do_test(struct vm86plus_struct *v86, unsigned long eip,
136 		    unsigned int rettype, unsigned int retarg,
137 		    const char *text)
138 {
139 	long ret;
140 
141 	printf("[RUN]\t%s from vm86 mode\n", text);
142 	v86->regs.eip = eip;
143 	ret = vm86(VM86_ENTER, v86);
144 
145 	if (ret == -1 && (errno == ENOSYS || errno == EPERM)) {
146 		printf("[SKIP]\tvm86 %s\n",
147 		       errno == ENOSYS ? "not supported" : "not allowed");
148 		return false;
149 	}
150 
151 	if (VM86_TYPE(ret) == VM86_INTx) {
152 		char trapname[32];
153 		int trapno = VM86_ARG(ret);
154 		if (trapno == 13)
155 			strcpy(trapname, "GP");
156 		else if (trapno == 5)
157 			strcpy(trapname, "BR");
158 		else if (trapno == 14)
159 			strcpy(trapname, "PF");
160 		else
161 			sprintf(trapname, "%d", trapno);
162 
163 		printf("[INFO]\tExited vm86 mode due to #%s\n", trapname);
164 	} else if (VM86_TYPE(ret) == VM86_UNKNOWN) {
165 		printf("[INFO]\tExited vm86 mode due to unhandled GP fault\n");
166 	} else if (VM86_TYPE(ret) == VM86_TRAP) {
167 		printf("[INFO]\tExited vm86 mode due to a trap (arg=%ld)\n",
168 		       VM86_ARG(ret));
169 	} else if (VM86_TYPE(ret) == VM86_SIGNAL) {
170 		printf("[INFO]\tExited vm86 mode due to a signal\n");
171 	} else if (VM86_TYPE(ret) == VM86_STI) {
172 		printf("[INFO]\tExited vm86 mode due to STI\n");
173 	} else {
174 		printf("[INFO]\tExited vm86 mode due to type %ld, arg %ld\n",
175 		       VM86_TYPE(ret), VM86_ARG(ret));
176 	}
177 
178 	if (rettype == -1 ||
179 	    (VM86_TYPE(ret) == rettype && VM86_ARG(ret) == retarg)) {
180 		printf("[OK]\tReturned correctly\n");
181 	} else {
182 		printf("[FAIL]\tIncorrect return reason (started at eip = 0x%lx, ended at eip = 0x%lx)\n", eip, v86->regs.eip);
183 		nerrs++;
184 	}
185 
186 	return true;
187 }
188 
do_umip_tests(struct vm86plus_struct * vm86,unsigned char * test_mem)189 void do_umip_tests(struct vm86plus_struct *vm86, unsigned char *test_mem)
190 {
191 	struct table_desc {
192 		unsigned short limit;
193 		unsigned long base;
194 	} __attribute__((packed));
195 
196 	/* Initialize variables with arbitrary values */
197 	struct table_desc gdt1 = { .base = 0x3c3c3c3c, .limit = 0x9999 };
198 	struct table_desc gdt2 = { .base = 0x1a1a1a1a, .limit = 0xaeae };
199 	struct table_desc idt1 = { .base = 0x7b7b7b7b, .limit = 0xf1f1 };
200 	struct table_desc idt2 = { .base = 0x89898989, .limit = 0x1313 };
201 	unsigned short msw1 = 0x1414, msw2 = 0x2525, msw3 = 3737;
202 
203 	/* UMIP -- exit with INT3 unless kernel emulation did not trap #GP */
204 	do_test(vm86, vmcode_umip - vmcode, VM86_TRAP, 3, "UMIP tests");
205 
206 	/* Results from displacement-only addressing */
207 	msw1 = *(unsigned short *)(test_mem + 2052);
208 	memcpy(&idt1, test_mem + 2054, sizeof(idt1));
209 	memcpy(&gdt1, test_mem + 2060, sizeof(gdt1));
210 
211 	/* Results from register-indirect addressing */
212 	msw2 = *(unsigned short *)(test_mem + 2066);
213 	memcpy(&idt2, test_mem + 2068, sizeof(idt2));
214 	memcpy(&gdt2, test_mem + 2074, sizeof(gdt2));
215 
216 	/* Results when using register operands */
217 	msw3 = *(unsigned short *)(test_mem + 2080);
218 
219 	printf("[INFO]\tResult from SMSW:[0x%04x]\n", msw1);
220 	printf("[INFO]\tResult from SIDT: limit[0x%04x]base[0x%08lx]\n",
221 	       idt1.limit, idt1.base);
222 	printf("[INFO]\tResult from SGDT: limit[0x%04x]base[0x%08lx]\n",
223 	       gdt1.limit, gdt1.base);
224 
225 	if (msw1 != msw2 || msw1 != msw3)
226 		printf("[FAIL]\tAll the results of SMSW should be the same.\n");
227 	else
228 		printf("[PASS]\tAll the results from SMSW are identical.\n");
229 
230 	if (memcmp(&gdt1, &gdt2, sizeof(gdt1)))
231 		printf("[FAIL]\tAll the results of SGDT should be the same.\n");
232 	else
233 		printf("[PASS]\tAll the results from SGDT are identical.\n");
234 
235 	if (memcmp(&idt1, &idt2, sizeof(idt1)))
236 		printf("[FAIL]\tAll the results of SIDT should be the same.\n");
237 	else
238 		printf("[PASS]\tAll the results from SIDT are identical.\n");
239 
240 	sethandler(SIGILL, sighandler, 0);
241 	do_test(vm86, vmcode_umip_str - vmcode, VM86_SIGNAL, 0,
242 		"STR instruction");
243 	clearhandler(SIGILL);
244 
245 	sethandler(SIGILL, sighandler, 0);
246 	do_test(vm86, vmcode_umip_sldt - vmcode, VM86_SIGNAL, 0,
247 		"SLDT instruction");
248 	clearhandler(SIGILL);
249 }
250 
main(void)251 int main(void)
252 {
253 	struct vm86plus_struct v86;
254 	unsigned char *addr = mmap((void *)load_addr, 4096,
255 				   PROT_READ | PROT_WRITE | PROT_EXEC,
256 				   MAP_ANONYMOUS | MAP_PRIVATE, -1,0);
257 	if (addr != (unsigned char *)load_addr)
258 		err(1, "mmap");
259 
260 	memcpy(addr, vmcode, end_vmcode - vmcode);
261 	addr[2048] = 2;
262 	addr[2050] = 3;
263 
264 	memset(&v86, 0, sizeof(v86));
265 
266 	v86.regs.cs = load_addr / 16;
267 	v86.regs.ss = load_addr / 16;
268 	v86.regs.ds = load_addr / 16;
269 	v86.regs.es = load_addr / 16;
270 
271 	/* Use the end of the page as our stack. */
272 	v86.regs.esp = 4096;
273 
274 	assert((v86.regs.cs & 3) == 0);	/* Looks like RPL = 0 */
275 
276 	/* #BR -- should deliver SIG??? */
277 	do_test(&v86, vmcode_bound - vmcode, VM86_INTx, 5, "#BR");
278 
279 	/*
280 	 * SYSENTER -- should cause #GP or #UD depending on CPU.
281 	 * Expected return type -1 means that we shouldn't validate
282 	 * the vm86 return value.  This will avoid problems on non-SEP
283 	 * CPUs.
284 	 */
285 	sethandler(SIGILL, sighandler, 0);
286 	do_test(&v86, vmcode_sysenter - vmcode, -1, 0, "SYSENTER");
287 	clearhandler(SIGILL);
288 
289 	/*
290 	 * SYSCALL would be a disaster in VM86 mode.  Fortunately,
291 	 * there is no kernel that both enables SYSCALL and sets
292 	 * EFER.SCE, so it's #UD on all systems.  But vm86 is
293 	 * buggy (or has a "feature"), so the SIGILL will actually
294 	 * be delivered.
295 	 */
296 	sethandler(SIGILL, sighandler, 0);
297 	do_test(&v86, vmcode_syscall - vmcode, VM86_SIGNAL, 0, "SYSCALL");
298 	clearhandler(SIGILL);
299 
300 	/* STI with VIP set */
301 	v86.regs.eflags |= X86_EFLAGS_VIP;
302 	v86.regs.eflags &= ~X86_EFLAGS_IF;
303 	do_test(&v86, vmcode_sti - vmcode, VM86_STI, 0, "STI with VIP set");
304 
305 	/* POPF with VIP set but IF clear: should not trap */
306 	v86.regs.eflags = X86_EFLAGS_VIP;
307 	v86.regs.eax = 0;
308 	do_test(&v86, vmcode_popf_hlt - vmcode, VM86_UNKNOWN, 0, "POPF with VIP set and IF clear");
309 
310 	/* POPF with VIP set and IF set: should trap */
311 	v86.regs.eflags = X86_EFLAGS_VIP;
312 	v86.regs.eax = X86_EFLAGS_IF;
313 	do_test(&v86, vmcode_popf_hlt - vmcode, VM86_STI, 0, "POPF with VIP and IF set");
314 
315 	/* POPF with VIP clear and IF set: should not trap */
316 	v86.regs.eflags = 0;
317 	v86.regs.eax = X86_EFLAGS_IF;
318 	do_test(&v86, vmcode_popf_hlt - vmcode, VM86_UNKNOWN, 0, "POPF with VIP clear and IF set");
319 
320 	v86.regs.eflags = 0;
321 
322 	/* INT3 -- should cause #BP */
323 	do_test(&v86, vmcode_int3 - vmcode, VM86_TRAP, 3, "INT3");
324 
325 	/* INT80 -- should exit with "INTx 0x80" */
326 	v86.regs.eax = (unsigned int)-1;
327 	do_test(&v86, vmcode_int80 - vmcode, VM86_INTx, 0x80, "int80");
328 
329 	/* UMIP -- should exit with INTx 0x80 unless UMIP was not disabled */
330 	do_umip_tests(&v86, addr);
331 
332 	/* Execute a null pointer */
333 	v86.regs.cs = 0;
334 	v86.regs.ss = 0;
335 	sethandler(SIGSEGV, sighandler, 0);
336 	got_signal = 0;
337 	if (do_test(&v86, 0, VM86_SIGNAL, 0, "Execute null pointer") &&
338 	    !got_signal) {
339 		printf("[FAIL]\tDid not receive SIGSEGV\n");
340 		nerrs++;
341 	}
342 	clearhandler(SIGSEGV);
343 
344 	/* Make sure nothing explodes if we fork. */
345 	if (fork() == 0)
346 		return 0;
347 
348 	return (nerrs == 0 ? 0 : 1);
349 }
350