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