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