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
9static 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 */
27void 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. */
43void 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. */
61void 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. */
73void 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
84static 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 */
106void 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
119static 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. */
145void 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 */
159void 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 */
174void 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
185/*
186 * A refcount_sub_and_test() by zero when the counter is at zero should act like
187 * refcount_sub_and_test() above when going negative.
188 */
189static void lkdtm_REFCOUNT_SUB_AND_TEST_ZERO(void)
190{
191	refcount_t neg = REFCOUNT_INIT(0);
192
193	pr_info("attempting bad refcount_sub_and_test() at zero\n");
194	if (refcount_sub_and_test(0, &neg))
195		pr_warn("Weird: refcount_sub_and_test() reported zero\n");
196
197	check_negative(&neg, 0);
198}
199
200static void check_from_zero(refcount_t *ref)
201{
202	switch (refcount_read(ref)) {
203	case 0:
204		pr_info("Zero detected: stayed at zero\n");
205		break;
206	case REFCOUNT_SATURATED:
207		pr_info("Zero detected: saturated\n");
208		break;
209	case REFCOUNT_MAX:
210		pr_warn("Zero detected: unsafely reset to max\n");
211		break;
212	default:
213		pr_info("Fail: zero not detected, incremented to %d\n",
214			refcount_read(ref));
215	}
216}
217
218/*
219 * A refcount_inc() from zero should pin to zero or saturate and may WARN.
220 */
221void lkdtm_REFCOUNT_INC_ZERO(void)
222{
223	refcount_t zero = REFCOUNT_INIT(0);
224
225	pr_info("attempting safe refcount_inc_not_zero() from zero\n");
226	if (!refcount_inc_not_zero(&zero)) {
227		pr_info("Good: zero detected\n");
228		if (refcount_read(&zero) == 0)
229			pr_info("Correctly stayed at zero\n");
230		else
231			pr_err("Fail: refcount went past zero!\n");
232	} else {
233		pr_err("Fail: Zero not detected!?\n");
234	}
235
236	pr_info("attempting bad refcount_inc() from zero\n");
237	refcount_inc(&zero);
238
239	check_from_zero(&zero);
240}
241
242/*
243 * A refcount_add() should act like refcount_inc() above when starting
244 * at zero.
245 */
246void lkdtm_REFCOUNT_ADD_ZERO(void)
247{
248	refcount_t zero = REFCOUNT_INIT(0);
249
250	pr_info("attempting safe refcount_add_not_zero() from zero\n");
251	if (!refcount_add_not_zero(3, &zero)) {
252		pr_info("Good: zero detected\n");
253		if (refcount_read(&zero) == 0)
254			pr_info("Correctly stayed at zero\n");
255		else
256			pr_err("Fail: refcount went past zero\n");
257	} else {
258		pr_err("Fail: Zero not detected!?\n");
259	}
260
261	pr_info("attempting bad refcount_add() from zero\n");
262	refcount_add(3, &zero);
263
264	check_from_zero(&zero);
265}
266
267static void check_saturated(refcount_t *ref)
268{
269	switch (refcount_read(ref)) {
270	case REFCOUNT_SATURATED:
271		pr_info("Saturation detected: still saturated\n");
272		break;
273	case REFCOUNT_MAX:
274		pr_warn("Saturation detected: unsafely reset to max\n");
275		break;
276	default:
277		pr_err("Fail: refcount went crazy: %d\n", refcount_read(ref));
278	}
279}
280
281/*
282 * A refcount_inc() from a saturated value should at most warn about
283 * being saturated already.
284 */
285void lkdtm_REFCOUNT_INC_SATURATED(void)
286{
287	refcount_t sat = REFCOUNT_INIT(REFCOUNT_SATURATED);
288
289	pr_info("attempting bad refcount_inc() from saturated\n");
290	refcount_inc(&sat);
291
292	check_saturated(&sat);
293}
294
295/* Should act like refcount_inc() above from saturated. */
296void lkdtm_REFCOUNT_DEC_SATURATED(void)
297{
298	refcount_t sat = REFCOUNT_INIT(REFCOUNT_SATURATED);
299
300	pr_info("attempting bad refcount_dec() from saturated\n");
301	refcount_dec(&sat);
302
303	check_saturated(&sat);
304}
305
306/* Should act like refcount_inc() above from saturated. */
307void lkdtm_REFCOUNT_ADD_SATURATED(void)
308{
309	refcount_t sat = REFCOUNT_INIT(REFCOUNT_SATURATED);
310
311	pr_info("attempting bad refcount_dec() from saturated\n");
312	refcount_add(8, &sat);
313
314	check_saturated(&sat);
315}
316
317/* Should act like refcount_inc() above from saturated. */
318void lkdtm_REFCOUNT_INC_NOT_ZERO_SATURATED(void)
319{
320	refcount_t sat = REFCOUNT_INIT(REFCOUNT_SATURATED);
321
322	pr_info("attempting bad refcount_inc_not_zero() from saturated\n");
323	if (!refcount_inc_not_zero(&sat))
324		pr_warn("Weird: refcount_inc_not_zero() reported zero\n");
325
326	check_saturated(&sat);
327}
328
329/* Should act like refcount_inc() above from saturated. */
330void lkdtm_REFCOUNT_ADD_NOT_ZERO_SATURATED(void)
331{
332	refcount_t sat = REFCOUNT_INIT(REFCOUNT_SATURATED);
333
334	pr_info("attempting bad refcount_add_not_zero() from saturated\n");
335	if (!refcount_add_not_zero(7, &sat))
336		pr_warn("Weird: refcount_add_not_zero() reported zero\n");
337
338	check_saturated(&sat);
339}
340
341/* Should act like refcount_inc() above from saturated. */
342void lkdtm_REFCOUNT_DEC_AND_TEST_SATURATED(void)
343{
344	refcount_t sat = REFCOUNT_INIT(REFCOUNT_SATURATED);
345
346	pr_info("attempting bad refcount_dec_and_test() from saturated\n");
347	if (refcount_dec_and_test(&sat))
348		pr_warn("Weird: refcount_dec_and_test() reported zero\n");
349
350	check_saturated(&sat);
351}
352
353/* Should act like refcount_inc() above from saturated. */
354void lkdtm_REFCOUNT_SUB_AND_TEST_SATURATED(void)
355{
356	refcount_t sat = REFCOUNT_INIT(REFCOUNT_SATURATED);
357
358	pr_info("attempting bad refcount_sub_and_test() from saturated\n");
359	if (refcount_sub_and_test(8, &sat))
360		pr_warn("Weird: refcount_sub_and_test() reported zero\n");
361
362	check_saturated(&sat);
363}
364
365/* Used to time the existing atomic_t when used for reference counting */
366void lkdtm_ATOMIC_TIMING(void)
367{
368	unsigned int i;
369	atomic_t count = ATOMIC_INIT(1);
370
371	for (i = 0; i < INT_MAX - 1; i++)
372		atomic_inc(&count);
373
374	for (i = INT_MAX; i > 0; i--)
375		if (atomic_dec_and_test(&count))
376			break;
377
378	if (i != 1)
379		pr_err("atomic timing: out of sync up/down cycle: %u\n", i - 1);
380	else
381		pr_info("atomic timing: done\n");
382}
383
384/*
385 * This can be compared to ATOMIC_TIMING when implementing fast refcount
386 * protections. Looking at the number of CPU cycles tells the real story
387 * about performance. For example:
388 *    cd /sys/kernel/debug/provoke-crash
389 *    perf stat -B -- cat <(echo REFCOUNT_TIMING) > DIRECT
390 */
391void lkdtm_REFCOUNT_TIMING(void)
392{
393	unsigned int i;
394	refcount_t count = REFCOUNT_INIT(1);
395
396	for (i = 0; i < INT_MAX - 1; i++)
397		refcount_inc(&count);
398
399	for (i = INT_MAX; i > 0; i--)
400		if (refcount_dec_and_test(&count))
401			break;
402
403	if (i != 1)
404		pr_err("refcount: out of sync up/down cycle: %u\n", i - 1);
405	else
406		pr_info("refcount timing: done\n");
407}
408