1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 * Copyright (c) 2020 Collabora Ltd.
4 *
5 * Test code for syscall user dispatch
6 */
7
8 #define _GNU_SOURCE
9 #include <sys/prctl.h>
10 #include <sys/sysinfo.h>
11 #include <sys/syscall.h>
12 #include <signal.h>
13
14 #include <asm/unistd.h>
15 #include "../kselftest_harness.h"
16
17 #ifndef PR_SET_SYSCALL_USER_DISPATCH
18 # define PR_SET_SYSCALL_USER_DISPATCH 59
19 # define PR_SYS_DISPATCH_OFF 0
20 # define PR_SYS_DISPATCH_ON 1
21 # define SYSCALL_DISPATCH_FILTER_ALLOW 0
22 # define SYSCALL_DISPATCH_FILTER_BLOCK 1
23 #endif
24
25 #ifndef SYS_USER_DISPATCH
26 # define SYS_USER_DISPATCH 2
27 #endif
28
29 #ifdef __NR_syscalls
30 # define MAGIC_SYSCALL_1 (__NR_syscalls + 1) /* Bad Linux syscall number */
31 #else
32 # define MAGIC_SYSCALL_1 (0xff00) /* Bad Linux syscall number */
33 #endif
34
35 #define SYSCALL_DISPATCH_ON(x) ((x) = SYSCALL_DISPATCH_FILTER_BLOCK)
36 #define SYSCALL_DISPATCH_OFF(x) ((x) = SYSCALL_DISPATCH_FILTER_ALLOW)
37
38 /* Test Summary:
39 *
40 * - dispatch_trigger_sigsys: Verify if PR_SET_SYSCALL_USER_DISPATCH is
41 * able to trigger SIGSYS on a syscall.
42 *
43 * - bad_selector: Test that a bad selector value triggers SIGSYS with
44 * si_errno EINVAL.
45 *
46 * - bad_prctl_param: Test that the API correctly rejects invalid
47 * parameters on prctl
48 *
49 * - dispatch_and_return: Test that a syscall is selectively dispatched
50 * to userspace depending on the value of selector.
51 *
52 * - disable_dispatch: Test that the PR_SYS_DISPATCH_OFF correctly
53 * disables the dispatcher
54 *
55 * - direct_dispatch_range: Test that a syscall within the allowed range
56 * can bypass the dispatcher.
57 */
58
TEST_SIGNAL(dispatch_trigger_sigsys,SIGSYS)59 TEST_SIGNAL(dispatch_trigger_sigsys, SIGSYS)
60 {
61 char sel = SYSCALL_DISPATCH_FILTER_ALLOW;
62 struct sysinfo info;
63 int ret;
64
65 ret = sysinfo(&info);
66 ASSERT_EQ(0, ret);
67
68 ret = prctl(PR_SET_SYSCALL_USER_DISPATCH, PR_SYS_DISPATCH_ON, 0, 0, &sel);
69 ASSERT_EQ(0, ret) {
70 TH_LOG("Kernel does not support CONFIG_SYSCALL_USER_DISPATCH");
71 }
72
73 SYSCALL_DISPATCH_ON(sel);
74
75 sysinfo(&info);
76
77 EXPECT_FALSE(true) {
78 TH_LOG("Unreachable!");
79 }
80 }
81
TEST(bad_prctl_param)82 TEST(bad_prctl_param)
83 {
84 char sel = SYSCALL_DISPATCH_FILTER_ALLOW;
85 int op;
86
87 /* Invalid op */
88 op = -1;
89 prctl(PR_SET_SYSCALL_USER_DISPATCH, op, 0, 0, &sel);
90 ASSERT_EQ(EINVAL, errno);
91
92 /* PR_SYS_DISPATCH_OFF */
93 op = PR_SYS_DISPATCH_OFF;
94
95 /* offset != 0 */
96 prctl(PR_SET_SYSCALL_USER_DISPATCH, op, 0x1, 0x0, 0);
97 EXPECT_EQ(EINVAL, errno);
98
99 /* len != 0 */
100 prctl(PR_SET_SYSCALL_USER_DISPATCH, op, 0x0, 0xff, 0);
101 EXPECT_EQ(EINVAL, errno);
102
103 /* sel != NULL */
104 prctl(PR_SET_SYSCALL_USER_DISPATCH, op, 0x0, 0x0, &sel);
105 EXPECT_EQ(EINVAL, errno);
106
107 /* Valid parameter */
108 errno = 0;
109 prctl(PR_SET_SYSCALL_USER_DISPATCH, op, 0x0, 0x0, 0x0);
110 EXPECT_EQ(0, errno);
111
112 /* PR_SYS_DISPATCH_ON */
113 op = PR_SYS_DISPATCH_ON;
114
115 /* Dispatcher region is bad (offset > 0 && len == 0) */
116 prctl(PR_SET_SYSCALL_USER_DISPATCH, op, 0x1, 0x0, &sel);
117 EXPECT_EQ(EINVAL, errno);
118 prctl(PR_SET_SYSCALL_USER_DISPATCH, op, -1L, 0x0, &sel);
119 EXPECT_EQ(EINVAL, errno);
120
121 /* Invalid selector */
122 prctl(PR_SET_SYSCALL_USER_DISPATCH, op, 0x0, 0x1, (void *) -1);
123 ASSERT_EQ(EFAULT, errno);
124
125 /*
126 * Dispatcher range overflows unsigned long
127 */
128 prctl(PR_SET_SYSCALL_USER_DISPATCH, PR_SYS_DISPATCH_ON, 1, -1L, &sel);
129 ASSERT_EQ(EINVAL, errno) {
130 TH_LOG("Should reject bad syscall range");
131 }
132
133 /*
134 * Allowed range overflows usigned long
135 */
136 prctl(PR_SET_SYSCALL_USER_DISPATCH, PR_SYS_DISPATCH_ON, -1L, 0x1, &sel);
137 ASSERT_EQ(EINVAL, errno) {
138 TH_LOG("Should reject bad syscall range");
139 }
140 }
141
142 /*
143 * Use global selector for handle_sigsys tests, to avoid passing
144 * selector to signal handler
145 */
146 char glob_sel;
147 int nr_syscalls_emulated;
148 int si_code;
149 int si_errno;
150
handle_sigsys(int sig,siginfo_t * info,void * ucontext)151 static void handle_sigsys(int sig, siginfo_t *info, void *ucontext)
152 {
153 si_code = info->si_code;
154 si_errno = info->si_errno;
155
156 if (info->si_syscall == MAGIC_SYSCALL_1)
157 nr_syscalls_emulated++;
158
159 /* In preparation for sigreturn. */
160 SYSCALL_DISPATCH_OFF(glob_sel);
161
162 /*
163 * The tests for argument handling assume that `syscall(x) == x`. This
164 * is a NOP on x86 because the syscall number is passed in %rax, which
165 * happens to also be the function ABI return register. Other
166 * architectures may need to swizzle the arguments around.
167 */
168 #if defined(__riscv)
169 /* REG_A7 is not defined in libc headers */
170 # define REG_A7 (REG_A0 + 7)
171
172 ((ucontext_t *)ucontext)->uc_mcontext.__gregs[REG_A0] =
173 ((ucontext_t *)ucontext)->uc_mcontext.__gregs[REG_A7];
174 #endif
175 }
176
TEST(dispatch_and_return)177 TEST(dispatch_and_return)
178 {
179 long ret;
180 struct sigaction act;
181 sigset_t mask;
182
183 glob_sel = 0;
184 nr_syscalls_emulated = 0;
185 si_code = 0;
186 si_errno = 0;
187
188 memset(&act, 0, sizeof(act));
189 sigemptyset(&mask);
190
191 act.sa_sigaction = handle_sigsys;
192 act.sa_flags = SA_SIGINFO;
193 act.sa_mask = mask;
194
195 ret = sigaction(SIGSYS, &act, NULL);
196 ASSERT_EQ(0, ret);
197
198 /* Make sure selector is good prior to prctl. */
199 SYSCALL_DISPATCH_OFF(glob_sel);
200
201 ret = prctl(PR_SET_SYSCALL_USER_DISPATCH, PR_SYS_DISPATCH_ON, 0, 0, &glob_sel);
202 ASSERT_EQ(0, ret) {
203 TH_LOG("Kernel does not support CONFIG_SYSCALL_USER_DISPATCH");
204 }
205
206 /* MAGIC_SYSCALL_1 doesn't exist. */
207 SYSCALL_DISPATCH_OFF(glob_sel);
208 ret = syscall(MAGIC_SYSCALL_1);
209 EXPECT_EQ(-1, ret) {
210 TH_LOG("Dispatch triggered unexpectedly");
211 }
212
213 /* MAGIC_SYSCALL_1 should be emulated. */
214 nr_syscalls_emulated = 0;
215 SYSCALL_DISPATCH_ON(glob_sel);
216
217 ret = syscall(MAGIC_SYSCALL_1);
218 EXPECT_EQ(MAGIC_SYSCALL_1, ret) {
219 TH_LOG("Failed to intercept syscall");
220 }
221 EXPECT_EQ(1, nr_syscalls_emulated) {
222 TH_LOG("Failed to emulate syscall");
223 }
224 ASSERT_EQ(SYS_USER_DISPATCH, si_code) {
225 TH_LOG("Bad si_code in SIGSYS");
226 }
227 ASSERT_EQ(0, si_errno) {
228 TH_LOG("Bad si_errno in SIGSYS");
229 }
230 }
231
TEST_SIGNAL(bad_selector,SIGSYS)232 TEST_SIGNAL(bad_selector, SIGSYS)
233 {
234 long ret;
235 struct sigaction act;
236 sigset_t mask;
237 struct sysinfo info;
238
239 glob_sel = SYSCALL_DISPATCH_FILTER_ALLOW;
240 nr_syscalls_emulated = 0;
241 si_code = 0;
242 si_errno = 0;
243
244 memset(&act, 0, sizeof(act));
245 sigemptyset(&mask);
246
247 act.sa_sigaction = handle_sigsys;
248 act.sa_flags = SA_SIGINFO;
249 act.sa_mask = mask;
250
251 ret = sigaction(SIGSYS, &act, NULL);
252 ASSERT_EQ(0, ret);
253
254 /* Make sure selector is good prior to prctl. */
255 SYSCALL_DISPATCH_OFF(glob_sel);
256
257 ret = prctl(PR_SET_SYSCALL_USER_DISPATCH, PR_SYS_DISPATCH_ON, 0, 0, &glob_sel);
258 ASSERT_EQ(0, ret) {
259 TH_LOG("Kernel does not support CONFIG_SYSCALL_USER_DISPATCH");
260 }
261
262 glob_sel = -1;
263
264 sysinfo(&info);
265
266 /* Even though it is ready to catch SIGSYS, the signal is
267 * supposed to be uncatchable.
268 */
269
270 EXPECT_FALSE(true) {
271 TH_LOG("Unreachable!");
272 }
273 }
274
TEST(disable_dispatch)275 TEST(disable_dispatch)
276 {
277 int ret;
278 struct sysinfo info;
279 char sel = 0;
280
281 ret = prctl(PR_SET_SYSCALL_USER_DISPATCH, PR_SYS_DISPATCH_ON, 0, 0, &sel);
282 ASSERT_EQ(0, ret) {
283 TH_LOG("Kernel does not support CONFIG_SYSCALL_USER_DISPATCH");
284 }
285
286 /* MAGIC_SYSCALL_1 doesn't exist. */
287 SYSCALL_DISPATCH_OFF(glob_sel);
288
289 ret = prctl(PR_SET_SYSCALL_USER_DISPATCH, PR_SYS_DISPATCH_OFF, 0, 0, 0);
290 EXPECT_EQ(0, ret) {
291 TH_LOG("Failed to unset syscall user dispatch");
292 }
293
294 /* Shouldn't have any effect... */
295 SYSCALL_DISPATCH_ON(glob_sel);
296
297 ret = syscall(__NR_sysinfo, &info);
298 EXPECT_EQ(0, ret) {
299 TH_LOG("Dispatch triggered unexpectedly");
300 }
301 }
302
TEST(direct_dispatch_range)303 TEST(direct_dispatch_range)
304 {
305 int ret = 0;
306 struct sysinfo info;
307 char sel = SYSCALL_DISPATCH_FILTER_ALLOW;
308
309 /*
310 * Instead of calculating libc addresses; allow the entire
311 * memory map and lock the selector.
312 */
313 ret = prctl(PR_SET_SYSCALL_USER_DISPATCH, PR_SYS_DISPATCH_ON, 0, -1L, &sel);
314 ASSERT_EQ(0, ret) {
315 TH_LOG("Kernel does not support CONFIG_SYSCALL_USER_DISPATCH");
316 }
317
318 SYSCALL_DISPATCH_ON(sel);
319
320 ret = sysinfo(&info);
321 ASSERT_EQ(0, ret) {
322 TH_LOG("Dispatch triggered unexpectedly");
323 }
324 }
325
326 TEST_HARNESS_MAIN
327