1 /*
2 * Copyright (c) 2021 Dell Inc. or its subsidiaries. All Rights Reserved.
3 * Copyright (c) 2022 The FreeBSD Foundation
4 *
5 * Portions of this software were developed by Mark Johnston under sponsorship
6 * from the FreeBSD Foundation.
7 *
8 * Redistribution and use in source and binary forms, with or without
9 * modification, are permitted provided that the following conditions
10 * are met:
11 * 1. Redistributions of source code must retain the above copyright
12 * notice, this list of conditions and the following disclaimer.
13 * 2. Redistributions in binary form must reproduce the above copyright
14 * notice, this list of conditions and the following disclaimer in the
15 * documentation and/or other materials provided with the distribution.
16 *
17 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
18 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
19 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
20 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
21 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
22 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
23 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
24 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
25 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
26 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
27 * SUCH DAMAGE.
28 */
29
30 /*
31 * Test behavior when a mapping of a shared shadow vm object is
32 * invalidated by COW from another mapping. In particular, when
33 * minherit(INHERT_SHARE) is applied to a COW mapping, a subsequently
34 * forked child process will share the parent's shadow object. Thus,
35 * pages already mapped into one sharing process may be written from
36 * another, triggering a copy into the shadow object. The VM system
37 * expects that a fully shadowed page is unmapped, but at one point the
38 * use of a shared shadow object could break this invariant.
39 *
40 * This is a regression test for an issue isolated by rlibby@FreeBSD.org
41 * from an issue detected by stress2's collapse.sh by jeff@FreeBSD.org.
42 * The issue became CVE-2021-29626.
43 *
44 * This file is written as an ATF test suite but may be compiled as a
45 * standalone program with -DSTANDALONE (and optionally -DDEBUG).
46 */
47
48 #include <sys/param.h>
49 #include <sys/mman.h>
50 #include <sys/procctl.h>
51 #include <sys/resource.h>
52 #include <sys/sysctl.h>
53 #include <sys/wait.h>
54
55 #include <machine/atomic.h>
56
57 #include <err.h>
58 #include <errno.h>
59 #include <stdbool.h>
60 #include <stddef.h>
61 #include <stdio.h>
62 #include <stdlib.h>
63 #include <unistd.h>
64
65 #ifdef STANDALONE
66 #define ATF_REQUIRE(x) do { \
67 if (!(x)) \
68 errx(1, "%s", #x); \
69 } while (0)
70 #else
71 #include <atf-c.h>
72 #endif
73
74 #ifdef DEBUG
75 #define dprintf(...) printf(__VA_ARGS__)
76 #else
77 #define dprintf(...)
78 #endif
79
80 #define DEPTH 5
81
82 #define FLAG_COLLAPSE 0x1
83 #define FLAG_BLOCK_XFER 0x2
84 #define FLAG_FULLMOD 0x4
85 #define FLAG_MASK (FLAG_COLLAPSE | FLAG_BLOCK_XFER | FLAG_FULLMOD)
86
87 struct shared_state {
88 void *p;
89 size_t len;
90 size_t modlen;
91 size_t pagesize;
92 bool collapse;
93 bool block_xfer;
94 bool lazy_cow;
95 bool okay;
96 volatile bool exiting[DEPTH];
97 volatile bool exit;
98 volatile bool p3_did_write;
99 };
100
101 /*
102 * Program flow. There are three or four processes that are descendants
103 * of the process running the test (P0), where arrows go from parents to
104 * children, and thicker arrows indicate sharing a certain memory region
105 * without COW semantics:
106 * P0 -> P1 -> P2 => P3
107 * \=> P4
108 * The main idea is that P1 maps a memory region, and that region is
109 * shared with P2/P3, but with COW semantics. When P3 modifies the
110 * memory, P2 ought to see that modification. P4 optionally exists to
111 * defeat a COW optimization.
112 */
113
114 #define child_err(...) do { \
115 ss->exit = true; \
116 err(1, __VA_ARGS__); \
117 } while (0)
118
119 #define child_errx(...) do { \
120 ss->exit = true; \
121 errx(1, __VA_ARGS__); \
122 } while (0)
123
124 #define SLEEP_TIME_US 1000
125
126 static void child(struct shared_state *ss, int depth);
127
128 static pid_t
child_fork(struct shared_state * ss,int depth)129 child_fork(struct shared_state *ss, int depth)
130 {
131 pid_t pid = fork();
132 if (pid == -1)
133 child_err("fork");
134 else if (pid == 0)
135 child(ss, depth);
136 return pid;
137 }
138
139 static void
child_fault(struct shared_state * ss)140 child_fault(struct shared_state *ss)
141 {
142 size_t i;
143
144 for (i = 0; i < ss->len; i += ss->pagesize)
145 (void)((volatile char *)ss->p)[i];
146 }
147
148 static void
child_write(struct shared_state * ss,int val,size_t len)149 child_write(struct shared_state *ss, int val, size_t len)
150 {
151 size_t i;
152
153 for (i = 0; i < len; i += ss->pagesize)
154 ((int *)ss->p)[i / sizeof(int)] = val;
155 atomic_thread_fence_rel();
156 }
157
158 static void
child_wait_p3_write(struct shared_state * ss)159 child_wait_p3_write(struct shared_state *ss)
160 {
161 while (!ss->p3_did_write) {
162 if (ss->exit)
163 exit(1);
164 usleep(SLEEP_TIME_US);
165 }
166 atomic_thread_fence_acq();
167 }
168
169 static void
child_verify(struct shared_state * ss,int depth,int newval,int oldval)170 child_verify(struct shared_state *ss, int depth, int newval, int oldval)
171 {
172 size_t i;
173 int expectval, foundval;
174
175 for (i = 0; i < ss->len; i += ss->pagesize) {
176 expectval = i < ss->modlen ? newval : oldval;
177 foundval = ((int *)ss->p)[i / sizeof(int)];
178 if (foundval == expectval)
179 continue;
180 child_errx("P%d saw %d but expected %d, %d was the old value",
181 depth, foundval, expectval, oldval);
182 }
183 }
184
185 static void
child(struct shared_state * ss,int depth)186 child(struct shared_state *ss, int depth)
187 {
188 pid_t mypid, oldval, pid;
189
190 if (depth < 1 || depth >= DEPTH)
191 child_errx("Bad depth %d", depth);
192 mypid = getpid();
193 dprintf("P%d (pid %d) started\n", depth, mypid);
194 switch (depth) {
195 case 1:
196 /* Shared memory undergoing test. */
197 ss->p = mmap(NULL, ss->len, PROT_READ | PROT_WRITE,
198 MAP_SHARED | MAP_ANON, -1, 0);
199 if (ss->p == MAP_FAILED)
200 child_err("mmap");
201
202 /* P1 stamps the shared memory. */
203 child_write(ss, mypid, ss->len);
204 if (!ss->lazy_cow) {
205 if (mlock(ss->p, ss->len) == -1)
206 child_err("mlock");
207 if (mprotect(ss->p, ss->len, PROT_READ) == -1)
208 child_err("mprotect");
209 }
210 if (ss->block_xfer) {
211 /*
212 * P4 is forked so that its existence blocks a page COW
213 * path where the page is simply transferred between
214 * objects, rather than being copied.
215 */
216 child_fork(ss, 4);
217 }
218 /*
219 * P1 specifies that modifications from its child processes not
220 * be shared with P1. Child process reads can be serviced from
221 * pages in P1's object, but writes must be COW'd.
222 */
223 if (minherit(ss->p, ss->len, INHERIT_COPY) != 0)
224 child_err("minherit");
225 /* Fork P2. */
226 child_fork(ss, depth + 1);
227 /* P1 and P4 wait for P3's writes before exiting. */
228 child_wait_p3_write(ss);
229 child_verify(ss, depth, mypid, mypid);
230 if (!ss->collapse) {
231 /* Hang around to prevent collapse. */
232 while (!ss->exit)
233 usleep(SLEEP_TIME_US);
234 }
235 /* Exit so the P2 -> P1/P4 shadow chain can collapse. */
236 break;
237 case 2:
238 /*
239 * P2 now specifies that modifications from its child processes
240 * be shared. P2 and P3 will share a shadow object.
241 */
242 if (minherit(ss->p, ss->len, INHERIT_SHARE) != 0)
243 child_err("minherit");
244
245 /*
246 * P2 faults a page in P1's object before P1 exits and the
247 * shadow chain is collapsed. This may be redundant if the
248 * (read-only) mappings were copied by fork(), but it doesn't
249 * hurt.
250 */
251 child_fault(ss);
252 oldval = atomic_load_acq_int(ss->p);
253
254 /* Fork P3. */
255 pid = child_fork(ss, depth + 1);
256 if (ss->collapse) {
257 /* Wait for P1 and P4 to exit, triggering collapse. */
258 while (!ss->exiting[1] ||
259 (ss->block_xfer && !ss->exiting[4]))
260 usleep(SLEEP_TIME_US);
261 /*
262 * This is racy, just guess at how long it may take
263 * them to finish exiting.
264 */
265 usleep(100 * 1000);
266 }
267 /* P2 waits for P3's modification. */
268 child_wait_p3_write(ss);
269 child_verify(ss, depth, pid, oldval);
270 ss->okay = true;
271 ss->exit = true;
272 break;
273 case 3:
274 /*
275 * Use mlock()+mprotect() to trigger the COW. This
276 * exercises a different COW handler than the one used
277 * for lazy faults.
278 */
279 if (!ss->lazy_cow) {
280 if (mlock(ss->p, ss->len) == -1)
281 child_err("mlock");
282 if (mprotect(ss->p, ss->len, PROT_READ | PROT_WRITE) ==
283 -1)
284 child_err("mprotect");
285 }
286
287 /*
288 * P3 writes the memory. A page is faulted into the shared
289 * P2/P3 shadow object. P2's mapping of the page in P1's
290 * object must now be shot down, or else P2 will wrongly
291 * continue to have that page mapped.
292 */
293 child_write(ss, mypid, ss->modlen);
294 ss->p3_did_write = true;
295 dprintf("P3 (pid %d) wrote its pid\n", mypid);
296 break;
297 case 4:
298 /* Just hang around until P3 is done writing. */
299 oldval = atomic_load_acq_int(ss->p);
300 child_wait_p3_write(ss);
301 child_verify(ss, depth, oldval, oldval);
302 break;
303 default:
304 child_errx("Bad depth %d", depth);
305 }
306
307 dprintf("P%d (pid %d) exiting\n", depth, mypid);
308 ss->exiting[depth] = true;
309 exit(0);
310 }
311
312 static void
do_one_shared_shadow_inval(bool lazy_cow,size_t pagesize,size_t len,unsigned int flags)313 do_one_shared_shadow_inval(bool lazy_cow, size_t pagesize, size_t len,
314 unsigned int flags)
315 {
316 struct shared_state *ss;
317 pid_t pid;
318 int status;
319
320 pid = getpid();
321
322 dprintf("P0 (pid %d) %s(collapse=%d, block_xfer=%d, full_mod=%d)\n",
323 pid, __func__, (int)collapse, (int)block_xfer, (int)full_mod);
324
325 ATF_REQUIRE(procctl(P_PID, pid, PROC_REAP_ACQUIRE, NULL) == 0);
326
327 /* Shared memory for coordination. */
328 ss = mmap(NULL, sizeof(*ss), PROT_READ | PROT_WRITE,
329 MAP_SHARED | MAP_ANON, -1, 0);
330 ATF_REQUIRE(ss != MAP_FAILED);
331
332 ss->len = len;
333 ss->modlen = (flags & FLAG_FULLMOD) ? ss->len : ss->len / 2;
334 ss->pagesize = pagesize;
335 ss->collapse = (flags & FLAG_COLLAPSE) != 0;
336 ss->block_xfer = (flags & FLAG_BLOCK_XFER) != 0;
337 ss->lazy_cow = lazy_cow;
338
339 pid = fork();
340 ATF_REQUIRE(pid != -1);
341 if (pid == 0)
342 child(ss, 1);
343
344 /* Wait for all descendants to exit. */
345 do {
346 pid = wait(&status);
347 ATF_REQUIRE(WIFEXITED(status));
348 } while (pid != -1 || errno != ECHILD);
349
350 atomic_thread_fence_acq();
351 ATF_REQUIRE(ss->okay);
352
353 ATF_REQUIRE(munmap(ss, sizeof(*ss)) == 0);
354 ATF_REQUIRE(procctl(P_PID, getpid(), PROC_REAP_RELEASE, NULL) == 0);
355 }
356
357 static void
do_shared_shadow_inval(bool lazy_cow)358 do_shared_shadow_inval(bool lazy_cow)
359 {
360 size_t largepagesize, pagesize, pagesizes[MAXPAGESIZES], sysctllen;
361
362 sysctllen = sizeof(pagesizes);
363 ATF_REQUIRE(sysctlbyname("hw.pagesizes", pagesizes, &sysctllen, NULL,
364 0) == 0);
365 ATF_REQUIRE(sysctllen >= sizeof(size_t));
366
367 pagesize = pagesizes[0];
368 largepagesize = MAXPAGESIZES >= 2 &&
369 sysctllen >= 2 * sizeof(size_t) && pagesizes[1] != 0 ?
370 pagesizes[1] : 2 * 1024 * 1024;
371
372 for (unsigned int i = 0; i <= FLAG_MASK; i++) {
373 do_one_shared_shadow_inval(lazy_cow, pagesize,
374 pagesize, i);
375 do_one_shared_shadow_inval(lazy_cow, pagesize,
376 2 * pagesize, i);
377 do_one_shared_shadow_inval(lazy_cow, pagesize,
378 largepagesize - pagesize, i);
379 do_one_shared_shadow_inval(lazy_cow, pagesize,
380 largepagesize, i);
381 do_one_shared_shadow_inval(lazy_cow, pagesize,
382 largepagesize + pagesize, i);
383 }
384 }
385
386 static void
do_shared_shadow_inval_eager(void)387 do_shared_shadow_inval_eager(void)
388 {
389 struct rlimit rl;
390
391 rl.rlim_cur = rl.rlim_max = RLIM_INFINITY;
392 ATF_REQUIRE(setrlimit(RLIMIT_MEMLOCK, &rl) == 0);
393
394 do_shared_shadow_inval(false);
395 }
396
397 static void
do_shared_shadow_inval_lazy(void)398 do_shared_shadow_inval_lazy(void)
399 {
400 do_shared_shadow_inval(true);
401 }
402
403 #ifdef STANDALONE
404 int
main(void)405 main(void)
406 {
407 do_shared_shadow_inval_lazy();
408 do_shared_shadow_inval_eager();
409 printf("pass\n");
410 }
411 #else
412 ATF_TC_WITHOUT_HEAD(shared_shadow_inval__lazy_cow);
ATF_TC_BODY(shared_shadow_inval__lazy_cow,tc)413 ATF_TC_BODY(shared_shadow_inval__lazy_cow, tc)
414 {
415 do_shared_shadow_inval_lazy();
416 }
417
418 ATF_TC(shared_shadow_inval__eager_cow);
ATF_TC_HEAD(shared_shadow_inval__eager_cow,tc)419 ATF_TC_HEAD(shared_shadow_inval__eager_cow, tc)
420 {
421 /* Needed to raise the mlock() limit. */
422 atf_tc_set_md_var(tc, "require.user", "root");
423 }
ATF_TC_BODY(shared_shadow_inval__eager_cow,tc)424 ATF_TC_BODY(shared_shadow_inval__eager_cow, tc)
425 {
426 do_shared_shadow_inval_eager();
427 }
428
ATF_TP_ADD_TCS(tp)429 ATF_TP_ADD_TCS(tp)
430 {
431 ATF_TP_ADD_TC(tp, shared_shadow_inval__lazy_cow);
432 ATF_TP_ADD_TC(tp, shared_shadow_inval__eager_cow);
433 return (atf_no_error());
434 }
435 #endif /* !STANDALONE */
436