1 // SPDX-License-Identifier: GPL-2.0
2
3 /*
4 * Tests for mremap w/ MREMAP_DONTUNMAP.
5 *
6 * Copyright 2020, Brian Geffon <bgeffon@google.com>
7 */
8 #define _GNU_SOURCE
9 #include <sys/mman.h>
10 #include <linux/mman.h>
11 #include <errno.h>
12 #include <stdio.h>
13 #include <stdlib.h>
14 #include <string.h>
15 #include <unistd.h>
16
17 #include "../kselftest.h"
18
19 unsigned long page_size;
20 char *page_buffer;
21
dump_maps(void)22 static void dump_maps(void)
23 {
24 char cmd[32];
25
26 snprintf(cmd, sizeof(cmd), "cat /proc/%d/maps", getpid());
27 system(cmd);
28 }
29
30 #define BUG_ON(condition, description) \
31 do { \
32 if (condition) { \
33 fprintf(stderr, "[FAIL]\t%s():%d\t%s:%s\n", __func__, \
34 __LINE__, (description), strerror(errno)); \
35 dump_maps(); \
36 exit(1); \
37 } \
38 } while (0)
39
40 // Try a simple operation for to "test" for kernel support this prevents
41 // reporting tests as failed when it's run on an older kernel.
kernel_support_for_mremap_dontunmap()42 static int kernel_support_for_mremap_dontunmap()
43 {
44 int ret = 0;
45 unsigned long num_pages = 1;
46 void *source_mapping = mmap(NULL, num_pages * page_size, PROT_NONE,
47 MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
48 BUG_ON(source_mapping == MAP_FAILED, "mmap");
49
50 // This simple remap should only fail if MREMAP_DONTUNMAP isn't
51 // supported.
52 void *dest_mapping =
53 mremap(source_mapping, num_pages * page_size, num_pages * page_size,
54 MREMAP_DONTUNMAP | MREMAP_MAYMOVE, 0);
55 if (dest_mapping == MAP_FAILED) {
56 ret = errno;
57 } else {
58 BUG_ON(munmap(dest_mapping, num_pages * page_size) == -1,
59 "unable to unmap destination mapping");
60 }
61
62 BUG_ON(munmap(source_mapping, num_pages * page_size) == -1,
63 "unable to unmap source mapping");
64 return ret;
65 }
66
67 // This helper will just validate that an entire mapping contains the expected
68 // byte.
check_region_contains_byte(void * addr,unsigned long size,char byte)69 static int check_region_contains_byte(void *addr, unsigned long size, char byte)
70 {
71 BUG_ON(size & (page_size - 1),
72 "check_region_contains_byte expects page multiples");
73 BUG_ON((unsigned long)addr & (page_size - 1),
74 "check_region_contains_byte expects page alignment");
75
76 memset(page_buffer, byte, page_size);
77
78 unsigned long num_pages = size / page_size;
79 unsigned long i;
80
81 // Compare each page checking that it contains our expected byte.
82 for (i = 0; i < num_pages; ++i) {
83 int ret =
84 memcmp(addr + (i * page_size), page_buffer, page_size);
85 if (ret) {
86 return ret;
87 }
88 }
89
90 return 0;
91 }
92
93 // this test validates that MREMAP_DONTUNMAP moves the pagetables while leaving
94 // the source mapping mapped.
mremap_dontunmap_simple()95 static void mremap_dontunmap_simple()
96 {
97 unsigned long num_pages = 5;
98
99 void *source_mapping =
100 mmap(NULL, num_pages * page_size, PROT_READ | PROT_WRITE,
101 MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
102 BUG_ON(source_mapping == MAP_FAILED, "mmap");
103
104 memset(source_mapping, 'a', num_pages * page_size);
105
106 // Try to just move the whole mapping anywhere (not fixed).
107 void *dest_mapping =
108 mremap(source_mapping, num_pages * page_size, num_pages * page_size,
109 MREMAP_DONTUNMAP | MREMAP_MAYMOVE, NULL);
110 BUG_ON(dest_mapping == MAP_FAILED, "mremap");
111
112 // Validate that the pages have been moved, we know they were moved if
113 // the dest_mapping contains a's.
114 BUG_ON(check_region_contains_byte
115 (dest_mapping, num_pages * page_size, 'a') != 0,
116 "pages did not migrate");
117 BUG_ON(check_region_contains_byte
118 (source_mapping, num_pages * page_size, 0) != 0,
119 "source should have no ptes");
120
121 BUG_ON(munmap(dest_mapping, num_pages * page_size) == -1,
122 "unable to unmap destination mapping");
123 BUG_ON(munmap(source_mapping, num_pages * page_size) == -1,
124 "unable to unmap source mapping");
125 }
126
127 // This test validates that MREMAP_DONTUNMAP on a shared mapping works as expected.
mremap_dontunmap_simple_shmem()128 static void mremap_dontunmap_simple_shmem()
129 {
130 unsigned long num_pages = 5;
131
132 int mem_fd = memfd_create("memfd", MFD_CLOEXEC);
133 BUG_ON(mem_fd < 0, "memfd_create");
134
135 BUG_ON(ftruncate(mem_fd, num_pages * page_size) < 0,
136 "ftruncate");
137
138 void *source_mapping =
139 mmap(NULL, num_pages * page_size, PROT_READ | PROT_WRITE,
140 MAP_FILE | MAP_SHARED, mem_fd, 0);
141 BUG_ON(source_mapping == MAP_FAILED, "mmap");
142
143 BUG_ON(close(mem_fd) < 0, "close");
144
145 memset(source_mapping, 'a', num_pages * page_size);
146
147 // Try to just move the whole mapping anywhere (not fixed).
148 void *dest_mapping =
149 mremap(source_mapping, num_pages * page_size, num_pages * page_size,
150 MREMAP_DONTUNMAP | MREMAP_MAYMOVE, NULL);
151 if (dest_mapping == MAP_FAILED && errno == EINVAL) {
152 // Old kernel which doesn't support MREMAP_DONTUNMAP on shmem.
153 BUG_ON(munmap(source_mapping, num_pages * page_size) == -1,
154 "unable to unmap source mapping");
155 return;
156 }
157
158 BUG_ON(dest_mapping == MAP_FAILED, "mremap");
159
160 // Validate that the pages have been moved, we know they were moved if
161 // the dest_mapping contains a's.
162 BUG_ON(check_region_contains_byte
163 (dest_mapping, num_pages * page_size, 'a') != 0,
164 "pages did not migrate");
165
166 // Because the region is backed by shmem, we will actually see the same
167 // memory at the source location still.
168 BUG_ON(check_region_contains_byte
169 (source_mapping, num_pages * page_size, 'a') != 0,
170 "source should have no ptes");
171
172 BUG_ON(munmap(dest_mapping, num_pages * page_size) == -1,
173 "unable to unmap destination mapping");
174 BUG_ON(munmap(source_mapping, num_pages * page_size) == -1,
175 "unable to unmap source mapping");
176 }
177
178 // This test validates MREMAP_DONTUNMAP will move page tables to a specific
179 // destination using MREMAP_FIXED, also while validating that the source
180 // remains intact.
mremap_dontunmap_simple_fixed()181 static void mremap_dontunmap_simple_fixed()
182 {
183 unsigned long num_pages = 5;
184
185 // Since we want to guarantee that we can remap to a point, we will
186 // create a mapping up front.
187 void *dest_mapping =
188 mmap(NULL, num_pages * page_size, PROT_READ | PROT_WRITE,
189 MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
190 BUG_ON(dest_mapping == MAP_FAILED, "mmap");
191 memset(dest_mapping, 'X', num_pages * page_size);
192
193 void *source_mapping =
194 mmap(NULL, num_pages * page_size, PROT_READ | PROT_WRITE,
195 MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
196 BUG_ON(source_mapping == MAP_FAILED, "mmap");
197 memset(source_mapping, 'a', num_pages * page_size);
198
199 void *remapped_mapping =
200 mremap(source_mapping, num_pages * page_size, num_pages * page_size,
201 MREMAP_FIXED | MREMAP_DONTUNMAP | MREMAP_MAYMOVE,
202 dest_mapping);
203 BUG_ON(remapped_mapping == MAP_FAILED, "mremap");
204 BUG_ON(remapped_mapping != dest_mapping,
205 "mremap should have placed the remapped mapping at dest_mapping");
206
207 // The dest mapping will have been unmap by mremap so we expect the Xs
208 // to be gone and replaced with a's.
209 BUG_ON(check_region_contains_byte
210 (dest_mapping, num_pages * page_size, 'a') != 0,
211 "pages did not migrate");
212
213 // And the source mapping will have had its ptes dropped.
214 BUG_ON(check_region_contains_byte
215 (source_mapping, num_pages * page_size, 0) != 0,
216 "source should have no ptes");
217
218 BUG_ON(munmap(dest_mapping, num_pages * page_size) == -1,
219 "unable to unmap destination mapping");
220 BUG_ON(munmap(source_mapping, num_pages * page_size) == -1,
221 "unable to unmap source mapping");
222 }
223
224 // This test validates that we can MREMAP_DONTUNMAP for a portion of an
225 // existing mapping.
mremap_dontunmap_partial_mapping()226 static void mremap_dontunmap_partial_mapping()
227 {
228 /*
229 * source mapping:
230 * --------------
231 * | aaaaaaaaaa |
232 * --------------
233 * to become:
234 * --------------
235 * | aaaaa00000 |
236 * --------------
237 * With the destination mapping containing 5 pages of As.
238 * ---------
239 * | aaaaa |
240 * ---------
241 */
242 unsigned long num_pages = 10;
243 void *source_mapping =
244 mmap(NULL, num_pages * page_size, PROT_READ | PROT_WRITE,
245 MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
246 BUG_ON(source_mapping == MAP_FAILED, "mmap");
247 memset(source_mapping, 'a', num_pages * page_size);
248
249 // We will grab the last 5 pages of the source and move them.
250 void *dest_mapping =
251 mremap(source_mapping + (5 * page_size), 5 * page_size,
252 5 * page_size,
253 MREMAP_DONTUNMAP | MREMAP_MAYMOVE, NULL);
254 BUG_ON(dest_mapping == MAP_FAILED, "mremap");
255
256 // We expect the first 5 pages of the source to contain a's and the
257 // final 5 pages to contain zeros.
258 BUG_ON(check_region_contains_byte(source_mapping, 5 * page_size, 'a') !=
259 0, "first 5 pages of source should have original pages");
260 BUG_ON(check_region_contains_byte
261 (source_mapping + (5 * page_size), 5 * page_size, 0) != 0,
262 "final 5 pages of source should have no ptes");
263
264 // Finally we expect the destination to have 5 pages worth of a's.
265 BUG_ON(check_region_contains_byte(dest_mapping, 5 * page_size, 'a') !=
266 0, "dest mapping should contain ptes from the source");
267
268 BUG_ON(munmap(dest_mapping, 5 * page_size) == -1,
269 "unable to unmap destination mapping");
270 BUG_ON(munmap(source_mapping, num_pages * page_size) == -1,
271 "unable to unmap source mapping");
272 }
273
274 // This test validates that we can remap over only a portion of a mapping.
mremap_dontunmap_partial_mapping_overwrite(void)275 static void mremap_dontunmap_partial_mapping_overwrite(void)
276 {
277 /*
278 * source mapping:
279 * ---------
280 * |aaaaa|
281 * ---------
282 * dest mapping initially:
283 * -----------
284 * |XXXXXXXXXX|
285 * ------------
286 * Source to become:
287 * ---------
288 * |00000|
289 * ---------
290 * With the destination mapping containing 5 pages of As.
291 * ------------
292 * |aaaaaXXXXX|
293 * ------------
294 */
295 void *source_mapping =
296 mmap(NULL, 5 * page_size, PROT_READ | PROT_WRITE,
297 MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
298 BUG_ON(source_mapping == MAP_FAILED, "mmap");
299 memset(source_mapping, 'a', 5 * page_size);
300
301 void *dest_mapping =
302 mmap(NULL, 10 * page_size, PROT_READ | PROT_WRITE,
303 MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
304 BUG_ON(dest_mapping == MAP_FAILED, "mmap");
305 memset(dest_mapping, 'X', 10 * page_size);
306
307 // We will grab the last 5 pages of the source and move them.
308 void *remapped_mapping =
309 mremap(source_mapping, 5 * page_size,
310 5 * page_size,
311 MREMAP_DONTUNMAP | MREMAP_MAYMOVE | MREMAP_FIXED, dest_mapping);
312 BUG_ON(dest_mapping == MAP_FAILED, "mremap");
313 BUG_ON(dest_mapping != remapped_mapping, "expected to remap to dest_mapping");
314
315 BUG_ON(check_region_contains_byte(source_mapping, 5 * page_size, 0) !=
316 0, "first 5 pages of source should have no ptes");
317
318 // Finally we expect the destination to have 5 pages worth of a's.
319 BUG_ON(check_region_contains_byte(dest_mapping, 5 * page_size, 'a') != 0,
320 "dest mapping should contain ptes from the source");
321
322 // Finally the last 5 pages shouldn't have been touched.
323 BUG_ON(check_region_contains_byte(dest_mapping + (5 * page_size),
324 5 * page_size, 'X') != 0,
325 "dest mapping should have retained the last 5 pages");
326
327 BUG_ON(munmap(dest_mapping, 10 * page_size) == -1,
328 "unable to unmap destination mapping");
329 BUG_ON(munmap(source_mapping, 5 * page_size) == -1,
330 "unable to unmap source mapping");
331 }
332
main(void)333 int main(void)
334 {
335 page_size = sysconf(_SC_PAGE_SIZE);
336
337 // test for kernel support for MREMAP_DONTUNMAP skipping the test if
338 // not.
339 if (kernel_support_for_mremap_dontunmap() != 0) {
340 printf("No kernel support for MREMAP_DONTUNMAP\n");
341 return KSFT_SKIP;
342 }
343
344 // Keep a page sized buffer around for when we need it.
345 page_buffer =
346 mmap(NULL, page_size, PROT_READ | PROT_WRITE,
347 MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
348 BUG_ON(page_buffer == MAP_FAILED, "unable to mmap a page.");
349
350 mremap_dontunmap_simple();
351 mremap_dontunmap_simple_shmem();
352 mremap_dontunmap_simple_fixed();
353 mremap_dontunmap_partial_mapping();
354 mremap_dontunmap_partial_mapping_overwrite();
355
356 BUG_ON(munmap(page_buffer, page_size) == -1,
357 "unable to unmap page buffer");
358
359 printf("OK\n");
360 return 0;
361 }
362