1 // SPDX-License-Identifier: GPL-2.0
2
3 /*
4 * Copyright 2020, Sandipan Das, IBM Corp.
5 *
6 * Test if the signal information reports the correct memory protection
7 * key upon getting a key access violation fault for a page that was
8 * attempted to be protected by two different keys from two competing
9 * threads at the same time.
10 */
11
12 #define _GNU_SOURCE
13 #include <stdio.h>
14 #include <stdlib.h>
15 #include <string.h>
16 #include <signal.h>
17
18 #include <unistd.h>
19 #include <pthread.h>
20 #include <sys/mman.h>
21
22 #include "pkeys.h"
23
24 #define PPC_INST_NOP 0x60000000
25 #define PPC_INST_BLR 0x4e800020
26 #define PROT_RWX (PROT_READ | PROT_WRITE | PROT_EXEC)
27
28 #define NUM_ITERATIONS 1000000
29
30 static volatile sig_atomic_t perm_pkey, rest_pkey;
31 static volatile sig_atomic_t rights, fault_count;
32 static volatile unsigned int *volatile fault_addr;
33 static pthread_barrier_t iteration_barrier;
34
35 static void segv_handler(int signum, siginfo_t *sinfo, void *ctx)
36 {
37 void *pgstart;
38 size_t pgsize;
39 int pkey;
40
41 pkey = siginfo_pkey(sinfo);
42
43 /* Check if this fault originated from a pkey access violation */
44 if (sinfo->si_code != SEGV_PKUERR) {
45 sigsafe_err("got a fault for an unexpected reason\n");
46 _exit(1);
47 }
48
49 /* Check if this fault originated from the expected address */
50 if (sinfo->si_addr != (void *) fault_addr) {
51 sigsafe_err("got a fault for an unexpected address\n");
52 _exit(1);
53 }
54
55 /* Check if this fault originated from the restrictive pkey */
56 if (pkey != rest_pkey) {
57 sigsafe_err("got a fault for an unexpected pkey\n");
58 _exit(1);
59 }
60
61 /* Check if too many faults have occurred for the same iteration */
62 if (fault_count > 0) {
63 sigsafe_err("got too many faults for the same address\n");
64 _exit(1);
65 }
66
67 pgsize = getpagesize();
68 pgstart = (void *) ((unsigned long) fault_addr & ~(pgsize - 1));
69
70 /*
71 * If the current fault occurred due to lack of execute rights,
72 * reassociate the page with the exec-only pkey since execute
73 * rights cannot be changed directly for the faulting pkey as
74 * IAMR is inaccessible from userspace.
75 *
76 * Otherwise, if the current fault occurred due to lack of
77 * read-write rights, change the AMR permission bits for the
78 * pkey.
79 *
80 * This will let the test continue.
81 */
82 if (rights == PKEY_DISABLE_EXECUTE &&
83 mprotect(pgstart, pgsize, PROT_EXEC))
84 _exit(1);
85 else
86 pkey_set_rights(pkey, 0);
87
88 fault_count++;
89 }
90
91 struct region {
92 unsigned long rights;
93 unsigned int *base;
94 size_t size;
95 };
96
97 static void *protect(void *p)
98 {
99 unsigned long rights;
100 unsigned int *base;
101 size_t size;
102 int tid, i;
103
104 tid = gettid();
105 base = ((struct region *) p)->base;
106 size = ((struct region *) p)->size;
107 FAIL_IF_EXIT(!base);
108
109 /* No read, write and execute restrictions */
110 rights = 0;
111
112 printf("tid %d, pkey permissions are %s\n", tid, pkey_rights(rights));
113
114 /* Allocate the permissive pkey */
115 perm_pkey = sys_pkey_alloc(0, rights);
116 FAIL_IF_EXIT(perm_pkey < 0);
117
118 /*
119 * Repeatedly try to protect the common region with a permissive
120 * pkey
121 */
122 for (i = 0; i < NUM_ITERATIONS; i++) {
123 /*
124 * Wait until the other thread has finished allocating the
125 * restrictive pkey or until the next iteration has begun
126 */
127 pthread_barrier_wait(&iteration_barrier);
128
129 /* Try to associate the permissive pkey with the region */
130 FAIL_IF_EXIT(sys_pkey_mprotect(base, size, PROT_RWX,
131 perm_pkey));
132 }
133
134 /* Free the permissive pkey */
135 sys_pkey_free(perm_pkey);
136
137 return NULL;
138 }
139
140 static void *protect_access(void *p)
141 {
142 size_t size, numinsns;
143 unsigned int *base;
144 int tid, i;
145
146 tid = gettid();
147 base = ((struct region *) p)->base;
148 size = ((struct region *) p)->size;
149 rights = ((struct region *) p)->rights;
150 numinsns = size / sizeof(base[0]);
151 FAIL_IF_EXIT(!base);
152
153 /* Allocate the restrictive pkey */
154 rest_pkey = sys_pkey_alloc(0, rights);
155 FAIL_IF_EXIT(rest_pkey < 0);
156
157 printf("tid %d, pkey permissions are %s\n", tid, pkey_rights(rights));
158 printf("tid %d, %s randomly in range [%p, %p]\n", tid,
159 (rights == PKEY_DISABLE_EXECUTE) ? "execute" :
160 (rights == PKEY_DISABLE_WRITE) ? "write" : "read",
161 base, base + numinsns);
162
163 /*
164 * Repeatedly try to protect the common region with a restrictive
165 * pkey and read, write or execute from it
166 */
167 for (i = 0; i < NUM_ITERATIONS; i++) {
168 /*
169 * Wait until the other thread has finished allocating the
170 * permissive pkey or until the next iteration has begun
171 */
172 pthread_barrier_wait(&iteration_barrier);
173
174 /* Try to associate the restrictive pkey with the region */
175 FAIL_IF_EXIT(sys_pkey_mprotect(base, size, PROT_RWX,
176 rest_pkey));
177
178 /* Choose a random instruction word address from the region */
179 fault_addr = base + (rand() % numinsns);
180 fault_count = 0;
181
182 switch (rights) {
183 /* Read protection test */
184 case PKEY_DISABLE_ACCESS:
185 /*
186 * Read an instruction word from the region and
187 * verify if it has not been overwritten to
188 * something unexpected
189 */
190 FAIL_IF_EXIT(*fault_addr != PPC_INST_NOP &&
191 *fault_addr != PPC_INST_BLR);
192 break;
193
194 /* Write protection test */
195 case PKEY_DISABLE_WRITE:
196 /*
197 * Write an instruction word to the region and
198 * verify if the overwrite has succeeded
199 */
200 *fault_addr = PPC_INST_BLR;
201 FAIL_IF_EXIT(*fault_addr != PPC_INST_BLR);
202 break;
203
204 /* Execute protection test */
205 case PKEY_DISABLE_EXECUTE:
206 /* Jump to the region and execute instructions */
207 asm volatile(
208 "mtctr %0; bctrl"
209 : : "r"(fault_addr) : "ctr", "lr");
210 break;
211 }
212
213 /*
214 * Restore the restrictions originally imposed by the
215 * restrictive pkey as the signal handler would have
216 * cleared out the corresponding AMR bits
217 */
218 pkey_set_rights(rest_pkey, rights);
219 }
220
221 /* Free restrictive pkey */
222 sys_pkey_free(rest_pkey);
223
224 return NULL;
225 }
226
227 static void reset_pkeys(unsigned long rights)
228 {
229 int pkeys[NR_PKEYS], i;
230
231 /* Exhaustively allocate all available pkeys */
232 for (i = 0; i < NR_PKEYS; i++)
233 pkeys[i] = sys_pkey_alloc(0, rights);
234
235 /* Free all allocated pkeys */
236 for (i = 0; i < NR_PKEYS; i++)
237 sys_pkey_free(pkeys[i]);
238 }
239
240 static int test(void)
241 {
242 pthread_t prot_thread, pacc_thread;
243 struct sigaction act;
244 pthread_attr_t attr;
245 size_t numinsns;
246 struct region r;
247 int ret, i;
248
249 srand(time(NULL));
250 ret = pkeys_unsupported();
251 if (ret)
252 return ret;
253
254 /* Allocate the region */
255 r.size = getpagesize();
256 r.base = mmap(NULL, r.size, PROT_RWX,
257 MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
258 FAIL_IF(r.base == MAP_FAILED);
259
260 /*
261 * Fill the region with no-ops with a branch at the end
262 * for returning to the caller
263 */
264 numinsns = r.size / sizeof(r.base[0]);
265 for (i = 0; i < numinsns - 1; i++)
266 r.base[i] = PPC_INST_NOP;
267 r.base[i] = PPC_INST_BLR;
268
269 /* Setup SIGSEGV handler */
270 act.sa_handler = 0;
271 act.sa_sigaction = segv_handler;
272 FAIL_IF(sigprocmask(SIG_SETMASK, 0, &act.sa_mask) != 0);
273 act.sa_flags = SA_SIGINFO;
274 act.sa_restorer = 0;
275 FAIL_IF(sigaction(SIGSEGV, &act, NULL) != 0);
276
277 /*
278 * For these tests, the parent process should clear all bits of
279 * AMR and IAMR, i.e. impose no restrictions, for all available
280 * pkeys. This will be the base for the initial AMR and IAMR
281 * values for all the test thread pairs.
282 *
283 * If the AMR and IAMR bits of all available pkeys are cleared
284 * before running the tests and a fault is generated when
285 * attempting to read, write or execute instructions from a
286 * pkey protected region, the pkey responsible for this must be
287 * the one from the protect-and-access thread since the other
288 * one is fully permissive. Despite that, if the pkey reported
289 * by siginfo is not the restrictive pkey, then there must be a
290 * kernel bug.
291 */
292 reset_pkeys(0);
293
294 /* Setup barrier for protect and protect-and-access threads */
295 FAIL_IF(pthread_attr_init(&attr) != 0);
296 FAIL_IF(pthread_barrier_init(&iteration_barrier, NULL, 2) != 0);
297
298 /* Setup and start protect and protect-and-read threads */
299 puts("starting thread pair (protect, protect-and-read)");
300 r.rights = PKEY_DISABLE_ACCESS;
301 FAIL_IF(pthread_create(&prot_thread, &attr, &protect, &r) != 0);
302 FAIL_IF(pthread_create(&pacc_thread, &attr, &protect_access, &r) != 0);
303 FAIL_IF(pthread_join(prot_thread, NULL) != 0);
304 FAIL_IF(pthread_join(pacc_thread, NULL) != 0);
305
306 /* Setup and start protect and protect-and-write threads */
307 puts("starting thread pair (protect, protect-and-write)");
308 r.rights = PKEY_DISABLE_WRITE;
309 FAIL_IF(pthread_create(&prot_thread, &attr, &protect, &r) != 0);
310 FAIL_IF(pthread_create(&pacc_thread, &attr, &protect_access, &r) != 0);
311 FAIL_IF(pthread_join(prot_thread, NULL) != 0);
312 FAIL_IF(pthread_join(pacc_thread, NULL) != 0);
313
314 /* Setup and start protect and protect-and-execute threads */
315 puts("starting thread pair (protect, protect-and-execute)");
316 r.rights = PKEY_DISABLE_EXECUTE;
317 FAIL_IF(pthread_create(&prot_thread, &attr, &protect, &r) != 0);
318 FAIL_IF(pthread_create(&pacc_thread, &attr, &protect_access, &r) != 0);
319 FAIL_IF(pthread_join(prot_thread, NULL) != 0);
320 FAIL_IF(pthread_join(pacc_thread, NULL) != 0);
321
322 /* Cleanup */
323 FAIL_IF(pthread_attr_destroy(&attr) != 0);
324 FAIL_IF(pthread_barrier_destroy(&iteration_barrier) != 0);
325 munmap(r.base, r.size);
326
327 return 0;
328 }
329
330 int main(void)
331 {
332 return test_harness(test, "pkey_siginfo");
333 }
334
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