drivers/misc/lkdtm/refcount.c

   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
   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  */
  27 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. */
  43 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. */
  61 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. */
  73 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
  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  */
 106 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
 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. */
 145 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  */
 159 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  */
 174 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
 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  */
 206 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  */
 231 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
 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  */
 270 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. */
 281 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. */
 292 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. */
 303 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. */
 315 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. */
 327 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. */
 339 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 */
 351 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  */
 376 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 }