1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * iopl.c - Test case for a Linux on Xen 64-bit bug
4  * Copyright (c) 2015 Andrew Lutomirski
5  */
6 
7 #define _GNU_SOURCE
8 #include <err.h>
9 #include <stdio.h>
10 #include <stdint.h>
11 #include <signal.h>
12 #include <setjmp.h>
13 #include <stdlib.h>
14 #include <string.h>
15 #include <errno.h>
16 #include <unistd.h>
17 #include <sys/types.h>
18 #include <sys/wait.h>
19 #include <stdbool.h>
20 #include <sched.h>
21 #include <sys/io.h>
22 
23 static int nerrs = 0;
24 
sethandler(int sig,void (* handler)(int,siginfo_t *,void *),int flags)25 static void sethandler(int sig, void (*handler)(int, siginfo_t *, void *),
26 		       int flags)
27 {
28 	struct sigaction sa;
29 	memset(&sa, 0, sizeof(sa));
30 	sa.sa_sigaction = handler;
31 	sa.sa_flags = SA_SIGINFO | flags;
32 	sigemptyset(&sa.sa_mask);
33 	if (sigaction(sig, &sa, 0))
34 		err(1, "sigaction");
35 
36 }
37 
clearhandler(int sig)38 static void clearhandler(int sig)
39 {
40 	struct sigaction sa;
41 	memset(&sa, 0, sizeof(sa));
42 	sa.sa_handler = SIG_DFL;
43 	sigemptyset(&sa.sa_mask);
44 	if (sigaction(sig, &sa, 0))
45 		err(1, "sigaction");
46 }
47 
48 static jmp_buf jmpbuf;
49 
sigsegv(int sig,siginfo_t * si,void * ctx_void)50 static void sigsegv(int sig, siginfo_t *si, void *ctx_void)
51 {
52 	siglongjmp(jmpbuf, 1);
53 }
54 
try_outb(unsigned short port)55 static bool try_outb(unsigned short port)
56 {
57 	sethandler(SIGSEGV, sigsegv, SA_RESETHAND);
58 	if (sigsetjmp(jmpbuf, 1) != 0) {
59 		return false;
60 	} else {
61 		asm volatile ("outb %%al, %w[port]"
62 			      : : [port] "Nd" (port), "a" (0));
63 		return true;
64 	}
65 	clearhandler(SIGSEGV);
66 }
67 
expect_ok_outb(unsigned short port)68 static void expect_ok_outb(unsigned short port)
69 {
70 	if (!try_outb(port)) {
71 		printf("[FAIL]\toutb to 0x%02hx failed\n", port);
72 		exit(1);
73 	}
74 
75 	printf("[OK]\toutb to 0x%02hx worked\n", port);
76 }
77 
expect_gp_outb(unsigned short port)78 static void expect_gp_outb(unsigned short port)
79 {
80 	if (try_outb(port)) {
81 		printf("[FAIL]\toutb to 0x%02hx worked\n", port);
82 		nerrs++;
83 	}
84 
85 	printf("[OK]\toutb to 0x%02hx failed\n", port);
86 }
87 
88 #define RET_FAULTED	0
89 #define RET_FAIL	1
90 #define RET_EMUL	2
91 
try_cli(void)92 static int try_cli(void)
93 {
94 	unsigned long flags;
95 
96 	sethandler(SIGSEGV, sigsegv, SA_RESETHAND);
97 	if (sigsetjmp(jmpbuf, 1) != 0) {
98 		return RET_FAULTED;
99 	} else {
100 		asm volatile("cli; pushf; pop %[flags]"
101 				: [flags] "=rm" (flags));
102 
103 		/* X86_FLAGS_IF */
104 		if (!(flags & (1 << 9)))
105 			return RET_FAIL;
106 		else
107 			return RET_EMUL;
108 	}
109 	clearhandler(SIGSEGV);
110 }
111 
try_sti(bool irqs_off)112 static int try_sti(bool irqs_off)
113 {
114 	unsigned long flags;
115 
116 	sethandler(SIGSEGV, sigsegv, SA_RESETHAND);
117 	if (sigsetjmp(jmpbuf, 1) != 0) {
118 		return RET_FAULTED;
119 	} else {
120 		asm volatile("sti; pushf; pop %[flags]"
121 				: [flags] "=rm" (flags));
122 
123 		/* X86_FLAGS_IF */
124 		if (irqs_off && (flags & (1 << 9)))
125 			return RET_FAIL;
126 		else
127 			return RET_EMUL;
128 	}
129 	clearhandler(SIGSEGV);
130 }
131 
expect_gp_sti(bool irqs_off)132 static void expect_gp_sti(bool irqs_off)
133 {
134 	int ret = try_sti(irqs_off);
135 
136 	switch (ret) {
137 	case RET_FAULTED:
138 		printf("[OK]\tSTI faulted\n");
139 		break;
140 	case RET_EMUL:
141 		printf("[OK]\tSTI NOPped\n");
142 		break;
143 	default:
144 		printf("[FAIL]\tSTI worked\n");
145 		nerrs++;
146 	}
147 }
148 
149 /*
150  * Returns whether it managed to disable interrupts.
151  */
test_cli(void)152 static bool test_cli(void)
153 {
154 	int ret = try_cli();
155 
156 	switch (ret) {
157 	case RET_FAULTED:
158 		printf("[OK]\tCLI faulted\n");
159 		break;
160 	case RET_EMUL:
161 		printf("[OK]\tCLI NOPped\n");
162 		break;
163 	default:
164 		printf("[FAIL]\tCLI worked\n");
165 		nerrs++;
166 		return true;
167 	}
168 
169 	return false;
170 }
171 
main(void)172 int main(void)
173 {
174 	cpu_set_t cpuset;
175 
176 	CPU_ZERO(&cpuset);
177 	CPU_SET(0, &cpuset);
178 	if (sched_setaffinity(0, sizeof(cpuset), &cpuset) != 0)
179 		err(1, "sched_setaffinity to CPU 0");
180 
181 	/* Probe for iopl support.  Note that iopl(0) works even as nonroot. */
182 	switch(iopl(3)) {
183 	case 0:
184 		break;
185 	case -ENOSYS:
186 		printf("[OK]\tiopl() nor supported\n");
187 		return 0;
188 	default:
189 		printf("[OK]\tiopl(3) failed (%d) -- try running as root\n",
190 		       errno);
191 		return 0;
192 	}
193 
194 	/* Make sure that CLI/STI are blocked even with IOPL level 3 */
195 	expect_gp_sti(test_cli());
196 	expect_ok_outb(0x80);
197 
198 	/* Establish an I/O bitmap to test the restore */
199 	if (ioperm(0x80, 1, 1) != 0)
200 		err(1, "ioperm(0x80, 1, 1) failed\n");
201 
202 	/* Restore our original state prior to starting the fork test. */
203 	if (iopl(0) != 0)
204 		err(1, "iopl(0)");
205 
206 	/*
207 	 * Verify that IOPL emulation is disabled and the I/O bitmap still
208 	 * works.
209 	 */
210 	expect_ok_outb(0x80);
211 	expect_gp_outb(0xed);
212 	/* Drop the I/O bitmap */
213 	if (ioperm(0x80, 1, 0) != 0)
214 		err(1, "ioperm(0x80, 1, 0) failed\n");
215 
216 	pid_t child = fork();
217 	if (child == -1)
218 		err(1, "fork");
219 
220 	if (child == 0) {
221 		printf("\tchild: set IOPL to 3\n");
222 		if (iopl(3) != 0)
223 			err(1, "iopl");
224 
225 		printf("[RUN]\tchild: write to 0x80\n");
226 		asm volatile ("outb %%al, $0x80" : : "a" (0));
227 
228 		return 0;
229 	} else {
230 		int status;
231 		if (waitpid(child, &status, 0) != child ||
232 		    !WIFEXITED(status)) {
233 			printf("[FAIL]\tChild died\n");
234 			nerrs++;
235 		} else if (WEXITSTATUS(status) != 0) {
236 			printf("[FAIL]\tChild failed\n");
237 			nerrs++;
238 		} else {
239 			printf("[OK]\tChild succeeded\n");
240 		}
241 	}
242 
243 	printf("[RUN]\tparent: write to 0x80 (should fail)\n");
244 
245 	expect_gp_outb(0x80);
246 	expect_gp_sti(test_cli());
247 
248 	/* Test the capability checks. */
249 	printf("\tiopl(3)\n");
250 	if (iopl(3) != 0)
251 		err(1, "iopl(3)");
252 
253 	printf("\tDrop privileges\n");
254 	if (setresuid(1, 1, 1) != 0) {
255 		printf("[WARN]\tDropping privileges failed\n");
256 		goto done;
257 	}
258 
259 	printf("[RUN]\tiopl(3) unprivileged but with IOPL==3\n");
260 	if (iopl(3) != 0) {
261 		printf("[FAIL]\tiopl(3) should work if iopl is already 3 even if unprivileged\n");
262 		nerrs++;
263 	}
264 
265 	printf("[RUN]\tiopl(0) unprivileged\n");
266 	if (iopl(0) != 0) {
267 		printf("[FAIL]\tiopl(0) should work if iopl is already 3 even if unprivileged\n");
268 		nerrs++;
269 	}
270 
271 	printf("[RUN]\tiopl(3) unprivileged\n");
272 	if (iopl(3) == 0) {
273 		printf("[FAIL]\tiopl(3) should fail if when unprivileged if iopl==0\n");
274 		nerrs++;
275 	} else {
276 		printf("[OK]\tFailed as expected\n");
277 	}
278 
279 done:
280 	return nerrs ? 1 : 0;
281 }
282