1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * This is for all the tests related to refcount bugs (e.g. overflow,
4 * underflow, reaching zero untested, etc).
5 */
6 #include "lkdtm.h"
7 #include <linux/refcount.h>
8
overflow_check(refcount_t * ref)9 static void overflow_check(refcount_t *ref)
10 {
11 switch (refcount_read(ref)) {
12 case REFCOUNT_SATURATED:
13 pr_info("Overflow detected: saturated\n");
14 break;
15 case REFCOUNT_MAX:
16 pr_warn("Overflow detected: unsafely reset to max\n");
17 break;
18 default:
19 pr_err("Fail: refcount wrapped to %d\n", refcount_read(ref));
20 }
21 }
22
23 /*
24 * A refcount_inc() above the maximum value of the refcount implementation,
25 * should at least saturate, and at most also WARN.
26 */
lkdtm_REFCOUNT_INC_OVERFLOW(void)27 static void lkdtm_REFCOUNT_INC_OVERFLOW(void)
28 {
29 refcount_t over = REFCOUNT_INIT(REFCOUNT_MAX - 1);
30
31 pr_info("attempting good refcount_inc() without overflow\n");
32 refcount_dec(&over);
33 refcount_inc(&over);
34
35 pr_info("attempting bad refcount_inc() overflow\n");
36 refcount_inc(&over);
37 refcount_inc(&over);
38
39 overflow_check(&over);
40 }
41
42 /* refcount_add() should behave just like refcount_inc() above. */
lkdtm_REFCOUNT_ADD_OVERFLOW(void)43 static void lkdtm_REFCOUNT_ADD_OVERFLOW(void)
44 {
45 refcount_t over = REFCOUNT_INIT(REFCOUNT_MAX - 1);
46
47 pr_info("attempting good refcount_add() without overflow\n");
48 refcount_dec(&over);
49 refcount_dec(&over);
50 refcount_dec(&over);
51 refcount_dec(&over);
52 refcount_add(4, &over);
53
54 pr_info("attempting bad refcount_add() overflow\n");
55 refcount_add(4, &over);
56
57 overflow_check(&over);
58 }
59
60 /* refcount_inc_not_zero() should behave just like refcount_inc() above. */
lkdtm_REFCOUNT_INC_NOT_ZERO_OVERFLOW(void)61 static void lkdtm_REFCOUNT_INC_NOT_ZERO_OVERFLOW(void)
62 {
63 refcount_t over = REFCOUNT_INIT(REFCOUNT_MAX);
64
65 pr_info("attempting bad refcount_inc_not_zero() overflow\n");
66 if (!refcount_inc_not_zero(&over))
67 pr_warn("Weird: refcount_inc_not_zero() reported zero\n");
68
69 overflow_check(&over);
70 }
71
72 /* refcount_add_not_zero() should behave just like refcount_inc() above. */
lkdtm_REFCOUNT_ADD_NOT_ZERO_OVERFLOW(void)73 static void lkdtm_REFCOUNT_ADD_NOT_ZERO_OVERFLOW(void)
74 {
75 refcount_t over = REFCOUNT_INIT(REFCOUNT_MAX);
76
77 pr_info("attempting bad refcount_add_not_zero() overflow\n");
78 if (!refcount_add_not_zero(6, &over))
79 pr_warn("Weird: refcount_add_not_zero() reported zero\n");
80
81 overflow_check(&over);
82 }
83
check_zero(refcount_t * ref)84 static void check_zero(refcount_t *ref)
85 {
86 switch (refcount_read(ref)) {
87 case REFCOUNT_SATURATED:
88 pr_info("Zero detected: saturated\n");
89 break;
90 case REFCOUNT_MAX:
91 pr_warn("Zero detected: unsafely reset to max\n");
92 break;
93 case 0:
94 pr_warn("Still at zero: refcount_inc/add() must not inc-from-0\n");
95 break;
96 default:
97 pr_err("Fail: refcount went crazy: %d\n", refcount_read(ref));
98 }
99 }
100
101 /*
102 * A refcount_dec(), as opposed to a refcount_dec_and_test(), when it hits
103 * zero it should either saturate (when inc-from-zero isn't protected)
104 * or stay at zero (when inc-from-zero is protected) and should WARN for both.
105 */
lkdtm_REFCOUNT_DEC_ZERO(void)106 static void lkdtm_REFCOUNT_DEC_ZERO(void)
107 {
108 refcount_t zero = REFCOUNT_INIT(2);
109
110 pr_info("attempting good refcount_dec()\n");
111 refcount_dec(&zero);
112
113 pr_info("attempting bad refcount_dec() to zero\n");
114 refcount_dec(&zero);
115
116 check_zero(&zero);
117 }
118
check_negative(refcount_t * ref,int start)119 static void check_negative(refcount_t *ref, int start)
120 {
121 /*
122 * refcount_t refuses to move a refcount at all on an
123 * over-sub, so we have to track our starting position instead of
124 * looking only at zero-pinning.
125 */
126 if (refcount_read(ref) == start) {
127 pr_warn("Still at %d: refcount_inc/add() must not inc-from-0\n",
128 start);
129 return;
130 }
131
132 switch (refcount_read(ref)) {
133 case REFCOUNT_SATURATED:
134 pr_info("Negative detected: saturated\n");
135 break;
136 case REFCOUNT_MAX:
137 pr_warn("Negative detected: unsafely reset to max\n");
138 break;
139 default:
140 pr_err("Fail: refcount went crazy: %d\n", refcount_read(ref));
141 }
142 }
143
144 /* A refcount_dec() going negative should saturate and may WARN. */
lkdtm_REFCOUNT_DEC_NEGATIVE(void)145 static void lkdtm_REFCOUNT_DEC_NEGATIVE(void)
146 {
147 refcount_t neg = REFCOUNT_INIT(0);
148
149 pr_info("attempting bad refcount_dec() below zero\n");
150 refcount_dec(&neg);
151
152 check_negative(&neg, 0);
153 }
154
155 /*
156 * A refcount_dec_and_test() should act like refcount_dec() above when
157 * going negative.
158 */
lkdtm_REFCOUNT_DEC_AND_TEST_NEGATIVE(void)159 static void lkdtm_REFCOUNT_DEC_AND_TEST_NEGATIVE(void)
160 {
161 refcount_t neg = REFCOUNT_INIT(0);
162
163 pr_info("attempting bad refcount_dec_and_test() below zero\n");
164 if (refcount_dec_and_test(&neg))
165 pr_warn("Weird: refcount_dec_and_test() reported zero\n");
166
167 check_negative(&neg, 0);
168 }
169
170 /*
171 * A refcount_sub_and_test() should act like refcount_dec_and_test()
172 * above when going negative.
173 */
lkdtm_REFCOUNT_SUB_AND_TEST_NEGATIVE(void)174 static void lkdtm_REFCOUNT_SUB_AND_TEST_NEGATIVE(void)
175 {
176 refcount_t neg = REFCOUNT_INIT(3);
177
178 pr_info("attempting bad refcount_sub_and_test() below zero\n");
179 if (refcount_sub_and_test(5, &neg))
180 pr_warn("Weird: refcount_sub_and_test() reported zero\n");
181
182 check_negative(&neg, 3);
183 }
184
check_from_zero(refcount_t * ref)185 static void check_from_zero(refcount_t *ref)
186 {
187 switch (refcount_read(ref)) {
188 case 0:
189 pr_info("Zero detected: stayed at zero\n");
190 break;
191 case REFCOUNT_SATURATED:
192 pr_info("Zero detected: saturated\n");
193 break;
194 case REFCOUNT_MAX:
195 pr_warn("Zero detected: unsafely reset to max\n");
196 break;
197 default:
198 pr_info("Fail: zero not detected, incremented to %d\n",
199 refcount_read(ref));
200 }
201 }
202
203 /*
204 * A refcount_inc() from zero should pin to zero or saturate and may WARN.
205 */
lkdtm_REFCOUNT_INC_ZERO(void)206 static void lkdtm_REFCOUNT_INC_ZERO(void)
207 {
208 refcount_t zero = REFCOUNT_INIT(0);
209
210 pr_info("attempting safe refcount_inc_not_zero() from zero\n");
211 if (!refcount_inc_not_zero(&zero)) {
212 pr_info("Good: zero detected\n");
213 if (refcount_read(&zero) == 0)
214 pr_info("Correctly stayed at zero\n");
215 else
216 pr_err("Fail: refcount went past zero!\n");
217 } else {
218 pr_err("Fail: Zero not detected!?\n");
219 }
220
221 pr_info("attempting bad refcount_inc() from zero\n");
222 refcount_inc(&zero);
223
224 check_from_zero(&zero);
225 }
226
227 /*
228 * A refcount_add() should act like refcount_inc() above when starting
229 * at zero.
230 */
lkdtm_REFCOUNT_ADD_ZERO(void)231 static void lkdtm_REFCOUNT_ADD_ZERO(void)
232 {
233 refcount_t zero = REFCOUNT_INIT(0);
234
235 pr_info("attempting safe refcount_add_not_zero() from zero\n");
236 if (!refcount_add_not_zero(3, &zero)) {
237 pr_info("Good: zero detected\n");
238 if (refcount_read(&zero) == 0)
239 pr_info("Correctly stayed at zero\n");
240 else
241 pr_err("Fail: refcount went past zero\n");
242 } else {
243 pr_err("Fail: Zero not detected!?\n");
244 }
245
246 pr_info("attempting bad refcount_add() from zero\n");
247 refcount_add(3, &zero);
248
249 check_from_zero(&zero);
250 }
251
check_saturated(refcount_t * ref)252 static void check_saturated(refcount_t *ref)
253 {
254 switch (refcount_read(ref)) {
255 case REFCOUNT_SATURATED:
256 pr_info("Saturation detected: still saturated\n");
257 break;
258 case REFCOUNT_MAX:
259 pr_warn("Saturation detected: unsafely reset to max\n");
260 break;
261 default:
262 pr_err("Fail: refcount went crazy: %d\n", refcount_read(ref));
263 }
264 }
265
266 /*
267 * A refcount_inc() from a saturated value should at most warn about
268 * being saturated already.
269 */
lkdtm_REFCOUNT_INC_SATURATED(void)270 static void lkdtm_REFCOUNT_INC_SATURATED(void)
271 {
272 refcount_t sat = REFCOUNT_INIT(REFCOUNT_SATURATED);
273
274 pr_info("attempting bad refcount_inc() from saturated\n");
275 refcount_inc(&sat);
276
277 check_saturated(&sat);
278 }
279
280 /* Should act like refcount_inc() above from saturated. */
lkdtm_REFCOUNT_DEC_SATURATED(void)281 static void lkdtm_REFCOUNT_DEC_SATURATED(void)
282 {
283 refcount_t sat = REFCOUNT_INIT(REFCOUNT_SATURATED);
284
285 pr_info("attempting bad refcount_dec() from saturated\n");
286 refcount_dec(&sat);
287
288 check_saturated(&sat);
289 }
290
291 /* Should act like refcount_inc() above from saturated. */
lkdtm_REFCOUNT_ADD_SATURATED(void)292 static void lkdtm_REFCOUNT_ADD_SATURATED(void)
293 {
294 refcount_t sat = REFCOUNT_INIT(REFCOUNT_SATURATED);
295
296 pr_info("attempting bad refcount_dec() from saturated\n");
297 refcount_add(8, &sat);
298
299 check_saturated(&sat);
300 }
301
302 /* Should act like refcount_inc() above from saturated. */
lkdtm_REFCOUNT_INC_NOT_ZERO_SATURATED(void)303 static void lkdtm_REFCOUNT_INC_NOT_ZERO_SATURATED(void)
304 {
305 refcount_t sat = REFCOUNT_INIT(REFCOUNT_SATURATED);
306
307 pr_info("attempting bad refcount_inc_not_zero() from saturated\n");
308 if (!refcount_inc_not_zero(&sat))
309 pr_warn("Weird: refcount_inc_not_zero() reported zero\n");
310
311 check_saturated(&sat);
312 }
313
314 /* Should act like refcount_inc() above from saturated. */
lkdtm_REFCOUNT_ADD_NOT_ZERO_SATURATED(void)315 static void lkdtm_REFCOUNT_ADD_NOT_ZERO_SATURATED(void)
316 {
317 refcount_t sat = REFCOUNT_INIT(REFCOUNT_SATURATED);
318
319 pr_info("attempting bad refcount_add_not_zero() from saturated\n");
320 if (!refcount_add_not_zero(7, &sat))
321 pr_warn("Weird: refcount_add_not_zero() reported zero\n");
322
323 check_saturated(&sat);
324 }
325
326 /* Should act like refcount_inc() above from saturated. */
lkdtm_REFCOUNT_DEC_AND_TEST_SATURATED(void)327 static void lkdtm_REFCOUNT_DEC_AND_TEST_SATURATED(void)
328 {
329 refcount_t sat = REFCOUNT_INIT(REFCOUNT_SATURATED);
330
331 pr_info("attempting bad refcount_dec_and_test() from saturated\n");
332 if (refcount_dec_and_test(&sat))
333 pr_warn("Weird: refcount_dec_and_test() reported zero\n");
334
335 check_saturated(&sat);
336 }
337
338 /* Should act like refcount_inc() above from saturated. */
lkdtm_REFCOUNT_SUB_AND_TEST_SATURATED(void)339 static void lkdtm_REFCOUNT_SUB_AND_TEST_SATURATED(void)
340 {
341 refcount_t sat = REFCOUNT_INIT(REFCOUNT_SATURATED);
342
343 pr_info("attempting bad refcount_sub_and_test() from saturated\n");
344 if (refcount_sub_and_test(8, &sat))
345 pr_warn("Weird: refcount_sub_and_test() reported zero\n");
346
347 check_saturated(&sat);
348 }
349
350 /* Used to time the existing atomic_t when used for reference counting */
lkdtm_ATOMIC_TIMING(void)351 static void lkdtm_ATOMIC_TIMING(void)
352 {
353 unsigned int i;
354 atomic_t count = ATOMIC_INIT(1);
355
356 for (i = 0; i < INT_MAX - 1; i++)
357 atomic_inc(&count);
358
359 for (i = INT_MAX; i > 0; i--)
360 if (atomic_dec_and_test(&count))
361 break;
362
363 if (i != 1)
364 pr_err("atomic timing: out of sync up/down cycle: %u\n", i - 1);
365 else
366 pr_info("atomic timing: done\n");
367 }
368
369 /*
370 * This can be compared to ATOMIC_TIMING when implementing fast refcount
371 * protections. Looking at the number of CPU cycles tells the real story
372 * about performance. For example:
373 * cd /sys/kernel/debug/provoke-crash
374 * perf stat -B -- cat <(echo REFCOUNT_TIMING) > DIRECT
375 */
lkdtm_REFCOUNT_TIMING(void)376 static void lkdtm_REFCOUNT_TIMING(void)
377 {
378 unsigned int i;
379 refcount_t count = REFCOUNT_INIT(1);
380
381 for (i = 0; i < INT_MAX - 1; i++)
382 refcount_inc(&count);
383
384 for (i = INT_MAX; i > 0; i--)
385 if (refcount_dec_and_test(&count))
386 break;
387
388 if (i != 1)
389 pr_err("refcount: out of sync up/down cycle: %u\n", i - 1);
390 else
391 pr_info("refcount timing: done\n");
392 }
393
394 static struct crashtype crashtypes[] = {
395 CRASHTYPE(REFCOUNT_INC_OVERFLOW),
396 CRASHTYPE(REFCOUNT_ADD_OVERFLOW),
397 CRASHTYPE(REFCOUNT_INC_NOT_ZERO_OVERFLOW),
398 CRASHTYPE(REFCOUNT_ADD_NOT_ZERO_OVERFLOW),
399 CRASHTYPE(REFCOUNT_DEC_ZERO),
400 CRASHTYPE(REFCOUNT_DEC_NEGATIVE),
401 CRASHTYPE(REFCOUNT_DEC_AND_TEST_NEGATIVE),
402 CRASHTYPE(REFCOUNT_SUB_AND_TEST_NEGATIVE),
403 CRASHTYPE(REFCOUNT_INC_ZERO),
404 CRASHTYPE(REFCOUNT_ADD_ZERO),
405 CRASHTYPE(REFCOUNT_INC_SATURATED),
406 CRASHTYPE(REFCOUNT_DEC_SATURATED),
407 CRASHTYPE(REFCOUNT_ADD_SATURATED),
408 CRASHTYPE(REFCOUNT_INC_NOT_ZERO_SATURATED),
409 CRASHTYPE(REFCOUNT_ADD_NOT_ZERO_SATURATED),
410 CRASHTYPE(REFCOUNT_DEC_AND_TEST_SATURATED),
411 CRASHTYPE(REFCOUNT_SUB_AND_TEST_SATURATED),
412 CRASHTYPE(ATOMIC_TIMING),
413 CRASHTYPE(REFCOUNT_TIMING),
414 };
415
416 struct crashtype_category refcount_crashtypes = {
417 .crashtypes = crashtypes,
418 .len = ARRAY_SIZE(crashtypes),
419 };
420