1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * Tests Memory Protection Keys (see Documentation/core-api/protection-keys.rst)
4 *
5 * The testcases in this file exercise various flows related to signal handling,
6 * using an alternate signal stack, with the default pkey (pkey 0) disabled.
7 *
8 * Compile with:
9 * gcc -mxsave -o pkey_sighandler_tests -O2 -g -std=gnu99 -pthread -Wall pkey_sighandler_tests.c -I../../../../tools/include -lrt -ldl -lm
10 * gcc -mxsave -m32 -o pkey_sighandler_tests -O2 -g -std=gnu99 -pthread -Wall pkey_sighandler_tests.c -I../../../../tools/include -lrt -ldl -lm
11 */
12 #define _GNU_SOURCE
13 #define __SANE_USERSPACE_TYPES__
14 #include <errno.h>
15 #include <sys/syscall.h>
16 #include <string.h>
17 #include <stdio.h>
18 #include <stdint.h>
19 #include <stdbool.h>
20 #include <signal.h>
21 #include <assert.h>
22 #include <stdlib.h>
23 #include <sys/mman.h>
24 #include <sys/types.h>
25 #include <sys/stat.h>
26 #include <unistd.h>
27 #include <pthread.h>
28 #include <limits.h>
29
30 #include "pkey-helpers.h"
31
32 #define STACK_SIZE PTHREAD_STACK_MIN
33
34 void expected_pkey_fault(int pkey) {}
35
36 pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
37 pthread_cond_t cond = PTHREAD_COND_INITIALIZER;
38 siginfo_t siginfo = {0};
39
40 /*
41 * We need to use inline assembly instead of glibc's syscall because glibc's
42 * syscall will attempt to access the PLT in order to call a library function
43 * which is protected by MPK 0 which we don't have access to.
44 */
45 static inline __always_inline
46 long syscall_raw(long n, long a1, long a2, long a3, long a4, long a5, long a6)
47 {
48 unsigned long ret;
49 #ifdef __x86_64__
50 register long r10 asm("r10") = a4;
51 register long r8 asm("r8") = a5;
52 register long r9 asm("r9") = a6;
53 asm volatile ("syscall"
54 : "=a"(ret)
55 : "a"(n), "D"(a1), "S"(a2), "d"(a3), "r"(r10), "r"(r8), "r"(r9)
56 : "rcx", "r11", "memory");
57 #elif defined __i386__
58 asm volatile ("int $0x80"
59 : "=a"(ret)
60 : "a"(n), "b"(a1), "c"(a2), "d"(a3), "S"(a4), "D"(a5)
61 : "memory");
62 #else
63 # error syscall_raw() not implemented
64 #endif
65 return ret;
66 }
67
68 static void sigsegv_handler(int signo, siginfo_t *info, void *ucontext)
69 {
70 pthread_mutex_lock(&mutex);
71
72 memcpy(&siginfo, info, sizeof(siginfo_t));
73
74 pthread_cond_signal(&cond);
75 pthread_mutex_unlock(&mutex);
76
77 syscall_raw(SYS_exit, 0, 0, 0, 0, 0, 0);
78 }
79
80 static void sigusr1_handler(int signo, siginfo_t *info, void *ucontext)
81 {
82 pthread_mutex_lock(&mutex);
83
84 memcpy(&siginfo, info, sizeof(siginfo_t));
85
86 pthread_cond_signal(&cond);
87 pthread_mutex_unlock(&mutex);
88 }
89
90 static void sigusr2_handler(int signo, siginfo_t *info, void *ucontext)
91 {
92 /*
93 * pkru should be the init_pkru value which enabled MPK 0 so
94 * we can use library functions.
95 */
96 printf("%s invoked.\n", __func__);
97 }
98
99 static void raise_sigusr2(void)
100 {
101 pid_t tid = 0;
102
103 tid = syscall_raw(SYS_gettid, 0, 0, 0, 0, 0, 0);
104
105 syscall_raw(SYS_tkill, tid, SIGUSR2, 0, 0, 0, 0);
106
107 /*
108 * We should return from the signal handler here and be able to
109 * return to the interrupted thread.
110 */
111 }
112
113 static void *thread_segv_with_pkey0_disabled(void *ptr)
114 {
115 /* Disable MPK 0 (and all others too) */
116 __write_pkey_reg(0x55555555);
117
118 /* Segfault (with SEGV_MAPERR) */
119 *(int *) (0x1) = 1;
120 return NULL;
121 }
122
123 static void *thread_segv_pkuerr_stack(void *ptr)
124 {
125 /* Disable MPK 0 (and all others too) */
126 __write_pkey_reg(0x55555555);
127
128 /* After we disable MPK 0, we can't access the stack to return */
129 return NULL;
130 }
131
132 static void *thread_segv_maperr_ptr(void *ptr)
133 {
134 stack_t *stack = ptr;
135 int *bad = (int *)1;
136
137 /*
138 * Setup alternate signal stack, which should be pkey_mprotect()ed by
139 * MPK 0. The thread's stack cannot be used for signals because it is
140 * not accessible by the default init_pkru value of 0x55555554.
141 */
142 syscall_raw(SYS_sigaltstack, (long)stack, 0, 0, 0, 0, 0);
143
144 /* Disable MPK 0. Only MPK 1 is enabled. */
145 __write_pkey_reg(0x55555551);
146
147 /* Segfault */
148 *bad = 1;
149 syscall_raw(SYS_exit, 0, 0, 0, 0, 0, 0);
150 return NULL;
151 }
152
153 /*
154 * Verify that the sigsegv handler is invoked when pkey 0 is disabled.
155 * Note that the new thread stack and the alternate signal stack is
156 * protected by MPK 0.
157 */
158 static void test_sigsegv_handler_with_pkey0_disabled(void)
159 {
160 struct sigaction sa;
161 pthread_attr_t attr;
162 pthread_t thr;
163
164 sa.sa_flags = SA_SIGINFO;
165
166 sa.sa_sigaction = sigsegv_handler;
167 sigemptyset(&sa.sa_mask);
168 if (sigaction(SIGSEGV, &sa, NULL) == -1) {
169 perror("sigaction");
170 exit(EXIT_FAILURE);
171 }
172
173 memset(&siginfo, 0, sizeof(siginfo));
174
175 pthread_attr_init(&attr);
176 pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
177
178 pthread_create(&thr, &attr, thread_segv_with_pkey0_disabled, NULL);
179
180 pthread_mutex_lock(&mutex);
181 while (siginfo.si_signo == 0)
182 pthread_cond_wait(&cond, &mutex);
183 pthread_mutex_unlock(&mutex);
184
185 ksft_test_result(siginfo.si_signo == SIGSEGV &&
186 siginfo.si_code == SEGV_MAPERR &&
187 siginfo.si_addr == (void *)1,
188 "%s\n", __func__);
189 }
190
191 /*
192 * Verify that the sigsegv handler is invoked when pkey 0 is disabled.
193 * Note that the new thread stack and the alternate signal stack is
194 * protected by MPK 0, which renders them inaccessible when MPK 0
195 * is disabled. So just the return from the thread should cause a
196 * segfault with SEGV_PKUERR.
197 */
198 static void test_sigsegv_handler_cannot_access_stack(void)
199 {
200 struct sigaction sa;
201 pthread_attr_t attr;
202 pthread_t thr;
203
204 sa.sa_flags = SA_SIGINFO;
205
206 sa.sa_sigaction = sigsegv_handler;
207 sigemptyset(&sa.sa_mask);
208 if (sigaction(SIGSEGV, &sa, NULL) == -1) {
209 perror("sigaction");
210 exit(EXIT_FAILURE);
211 }
212
213 memset(&siginfo, 0, sizeof(siginfo));
214
215 pthread_attr_init(&attr);
216 pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
217
218 pthread_create(&thr, &attr, thread_segv_pkuerr_stack, NULL);
219
220 pthread_mutex_lock(&mutex);
221 while (siginfo.si_signo == 0)
222 pthread_cond_wait(&cond, &mutex);
223 pthread_mutex_unlock(&mutex);
224
225 ksft_test_result(siginfo.si_signo == SIGSEGV &&
226 siginfo.si_code == SEGV_PKUERR,
227 "%s\n", __func__);
228 }
229
230 /*
231 * Verify that the sigsegv handler that uses an alternate signal stack
232 * is correctly invoked for a thread which uses a non-zero MPK to protect
233 * its own stack, and disables all other MPKs (including 0).
234 */
235 static void test_sigsegv_handler_with_different_pkey_for_stack(void)
236 {
237 struct sigaction sa;
238 static stack_t sigstack;
239 void *stack;
240 int pkey;
241 int parent_pid = 0;
242 int child_pid = 0;
243
244 sa.sa_flags = SA_SIGINFO | SA_ONSTACK;
245
246 sa.sa_sigaction = sigsegv_handler;
247
248 sigemptyset(&sa.sa_mask);
249 if (sigaction(SIGSEGV, &sa, NULL) == -1) {
250 perror("sigaction");
251 exit(EXIT_FAILURE);
252 }
253
254 stack = mmap(0, STACK_SIZE, PROT_READ | PROT_WRITE,
255 MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
256
257 assert(stack != MAP_FAILED);
258
259 /* Allow access to MPK 0 and MPK 1 */
260 __write_pkey_reg(0x55555550);
261
262 /* Protect the new stack with MPK 1 */
263 pkey = pkey_alloc(0, 0);
264 pkey_mprotect(stack, STACK_SIZE, PROT_READ | PROT_WRITE, pkey);
265
266 /* Set up alternate signal stack that will use the default MPK */
267 sigstack.ss_sp = mmap(0, STACK_SIZE, PROT_READ | PROT_WRITE | PROT_EXEC,
268 MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
269 sigstack.ss_flags = 0;
270 sigstack.ss_size = STACK_SIZE;
271
272 memset(&siginfo, 0, sizeof(siginfo));
273
274 /* Use clone to avoid newer glibcs using rseq on new threads */
275 long ret = syscall_raw(SYS_clone,
276 CLONE_VM | CLONE_FS | CLONE_FILES |
277 CLONE_SIGHAND | CLONE_THREAD | CLONE_SYSVSEM |
278 CLONE_PARENT_SETTID | CLONE_CHILD_CLEARTID |
279 CLONE_DETACHED,
280 (long) ((char *)(stack) + STACK_SIZE),
281 (long) &parent_pid,
282 (long) &child_pid, 0, 0);
283
284 if (ret < 0) {
285 errno = -ret;
286 perror("clone");
287 } else if (ret == 0) {
288 thread_segv_maperr_ptr(&sigstack);
289 syscall_raw(SYS_exit, 0, 0, 0, 0, 0, 0);
290 }
291
292 pthread_mutex_lock(&mutex);
293 while (siginfo.si_signo == 0)
294 pthread_cond_wait(&cond, &mutex);
295 pthread_mutex_unlock(&mutex);
296
297 ksft_test_result(siginfo.si_signo == SIGSEGV &&
298 siginfo.si_code == SEGV_MAPERR &&
299 siginfo.si_addr == (void *)1,
300 "%s\n", __func__);
301 }
302
303 /*
304 * Verify that the PKRU value set by the application is correctly
305 * restored upon return from signal handling.
306 */
307 static void test_pkru_preserved_after_sigusr1(void)
308 {
309 struct sigaction sa;
310 unsigned long pkru = 0x45454544;
311
312 sa.sa_flags = SA_SIGINFO;
313
314 sa.sa_sigaction = sigusr1_handler;
315 sigemptyset(&sa.sa_mask);
316 if (sigaction(SIGUSR1, &sa, NULL) == -1) {
317 perror("sigaction");
318 exit(EXIT_FAILURE);
319 }
320
321 memset(&siginfo, 0, sizeof(siginfo));
322
323 __write_pkey_reg(pkru);
324
325 raise(SIGUSR1);
326
327 pthread_mutex_lock(&mutex);
328 while (siginfo.si_signo == 0)
329 pthread_cond_wait(&cond, &mutex);
330 pthread_mutex_unlock(&mutex);
331
332 /* Ensure the pkru value is the same after returning from signal. */
333 ksft_test_result(pkru == __read_pkey_reg() &&
334 siginfo.si_signo == SIGUSR1,
335 "%s\n", __func__);
336 }
337
338 static noinline void *thread_sigusr2_self(void *ptr)
339 {
340 /*
341 * A const char array like "Resuming after SIGUSR2" won't be stored on
342 * the stack and the code could access it via an offset from the program
343 * counter. This makes sure it's on the function's stack frame.
344 */
345 char str[] = {'R', 'e', 's', 'u', 'm', 'i', 'n', 'g', ' ',
346 'a', 'f', 't', 'e', 'r', ' ',
347 'S', 'I', 'G', 'U', 'S', 'R', '2',
348 '.', '.', '.', '\n', '\0'};
349 stack_t *stack = ptr;
350
351 /*
352 * Setup alternate signal stack, which should be pkey_mprotect()ed by
353 * MPK 0. The thread's stack cannot be used for signals because it is
354 * not accessible by the default init_pkru value of 0x55555554.
355 */
356 syscall(SYS_sigaltstack, (long)stack, 0, 0, 0, 0, 0);
357
358 /* Disable MPK 0. Only MPK 2 is enabled. */
359 __write_pkey_reg(0x55555545);
360
361 raise_sigusr2();
362
363 /* Do something, to show the thread resumed execution after the signal */
364 syscall_raw(SYS_write, 1, (long) str, sizeof(str) - 1, 0, 0, 0);
365
366 /*
367 * We can't return to test_pkru_sigreturn because it
368 * will attempt to use a %rbp value which is on the stack
369 * of the main thread.
370 */
371 syscall_raw(SYS_exit, 0, 0, 0, 0, 0, 0);
372 return NULL;
373 }
374
375 /*
376 * Verify that sigreturn is able to restore altstack even if the thread had
377 * disabled pkey 0.
378 */
379 static void test_pkru_sigreturn(void)
380 {
381 struct sigaction sa = {0};
382 static stack_t sigstack;
383 void *stack;
384 int pkey;
385 int parent_pid = 0;
386 int child_pid = 0;
387
388 sa.sa_handler = SIG_DFL;
389 sa.sa_flags = 0;
390 sigemptyset(&sa.sa_mask);
391
392 /*
393 * For this testcase, we do not want to handle SIGSEGV. Reset handler
394 * to default so that the application can crash if it receives SIGSEGV.
395 */
396 if (sigaction(SIGSEGV, &sa, NULL) == -1) {
397 perror("sigaction");
398 exit(EXIT_FAILURE);
399 }
400
401 sa.sa_flags = SA_SIGINFO | SA_ONSTACK;
402 sa.sa_sigaction = sigusr2_handler;
403 sigemptyset(&sa.sa_mask);
404
405 if (sigaction(SIGUSR2, &sa, NULL) == -1) {
406 perror("sigaction");
407 exit(EXIT_FAILURE);
408 }
409
410 stack = mmap(0, STACK_SIZE, PROT_READ | PROT_WRITE,
411 MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
412
413 assert(stack != MAP_FAILED);
414
415 /*
416 * Allow access to MPK 0 and MPK 2. The child thread (to be created
417 * later in this flow) will have its stack protected by MPK 2, whereas
418 * the current thread's stack is protected by the default MPK 0. Hence
419 * both need to be enabled.
420 */
421 __write_pkey_reg(0x55555544);
422
423 /* Protect the stack with MPK 2 */
424 pkey = pkey_alloc(0, 0);
425 pkey_mprotect(stack, STACK_SIZE, PROT_READ | PROT_WRITE, pkey);
426
427 /* Set up alternate signal stack that will use the default MPK */
428 sigstack.ss_sp = mmap(0, STACK_SIZE, PROT_READ | PROT_WRITE | PROT_EXEC,
429 MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
430 sigstack.ss_flags = 0;
431 sigstack.ss_size = STACK_SIZE;
432
433 /* Use clone to avoid newer glibcs using rseq on new threads */
434 long ret = syscall_raw(SYS_clone,
435 CLONE_VM | CLONE_FS | CLONE_FILES |
436 CLONE_SIGHAND | CLONE_THREAD | CLONE_SYSVSEM |
437 CLONE_PARENT_SETTID | CLONE_CHILD_CLEARTID |
438 CLONE_DETACHED,
439 (long) ((char *)(stack) + STACK_SIZE),
440 (long) &parent_pid,
441 (long) &child_pid, 0, 0);
442
443 if (ret < 0) {
444 errno = -ret;
445 perror("clone");
446 } else if (ret == 0) {
447 thread_sigusr2_self(&sigstack);
448 syscall_raw(SYS_exit, 0, 0, 0, 0, 0, 0);
449 }
450
451 child_pid = ret;
452 /* Check that thread exited */
453 do {
454 sched_yield();
455 ret = syscall_raw(SYS_tkill, child_pid, 0, 0, 0, 0, 0);
456 } while (ret != -ESRCH && ret != -EINVAL);
457
458 ksft_test_result_pass("%s\n", __func__);
459 }
460
461 static void (*pkey_tests[])(void) = {
462 test_sigsegv_handler_with_pkey0_disabled,
463 test_sigsegv_handler_cannot_access_stack,
464 test_sigsegv_handler_with_different_pkey_for_stack,
465 test_pkru_preserved_after_sigusr1,
466 test_pkru_sigreturn
467 };
468
469 int main(int argc, char *argv[])
470 {
471 int i;
472
473 ksft_print_header();
474 ksft_set_plan(ARRAY_SIZE(pkey_tests));
475
476 for (i = 0; i < ARRAY_SIZE(pkey_tests); i++)
477 (*pkey_tests[i])();
478
479 ksft_finished();
480 return 0;
481 }
482
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