lib/test_stackinit.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Test cases for compiler-based stack variable zeroing via future
   4  * compiler flags or CONFIG_GCC_PLUGIN_STRUCTLEAK*.
   5  */
   6 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
   7
   8 #include <linux/init.h>
   9 #include <linux/kernel.h>
  10 #include <linux/module.h>
  11 #include <linux/string.h>
  12
  13 /* Exfiltration buffer. */
  14 #define MAX_VAR_SIZE    128
  15 static u8 check_buf[MAX_VAR_SIZE];
  16
  17 /* Character array to trigger stack protector in all functions. */
  18 #define VAR_BUFFER       32
  19
  20 /* Volatile mask to convince compiler to copy memory with 0xff. */
  21 static volatile u8 forced_mask = 0xff;
  22
  23 /* Location and size tracking to validate fill and test are colocated. */
  24 static void *fill_start, *target_start;
  25 static size_t fill_size, target_size;
  26
  27 static bool range_contains(char *haystack_start, size_t haystack_size,
  28                            char *needle_start, size_t needle_size)
  29 {
  30         if (needle_start >= haystack_start &&
  31             needle_start + needle_size <= haystack_start + haystack_size)
  32                 return true;
  33         return false;
  34 }
  35
  36 #define DO_NOTHING_TYPE_SCALAR(var_type)        var_type
  37 #define DO_NOTHING_TYPE_STRING(var_type)        void
  38 #define DO_NOTHING_TYPE_STRUCT(var_type)        void
  39
  40 #define DO_NOTHING_RETURN_SCALAR(ptr)           *(ptr)
  41 #define DO_NOTHING_RETURN_STRING(ptr)           /**/
  42 #define DO_NOTHING_RETURN_STRUCT(ptr)           /**/
  43
  44 #define DO_NOTHING_CALL_SCALAR(var, name)                       \
  45                 (var) = do_nothing_ ## name(&(var))
  46 #define DO_NOTHING_CALL_STRING(var, name)                       \
  47                 do_nothing_ ## name(var)
  48 #define DO_NOTHING_CALL_STRUCT(var, name)                       \
  49                 do_nothing_ ## name(&(var))
  50
  51 #define FETCH_ARG_SCALAR(var)           &var
  52 #define FETCH_ARG_STRING(var)           var
  53 #define FETCH_ARG_STRUCT(var)           &var
  54
  55 #define FILL_SIZE_STRING                16
  56
  57 #define INIT_CLONE_SCALAR               /**/
  58 #define INIT_CLONE_STRING               [FILL_SIZE_STRING]
  59 #define INIT_CLONE_STRUCT               /**/
  60
  61 #define INIT_SCALAR_none                /**/
  62 #define INIT_SCALAR_zero                = 0
  63
  64 #define INIT_STRING_none                [FILL_SIZE_STRING] /**/
  65 #define INIT_STRING_zero                [FILL_SIZE_STRING] = { }
  66
  67 #define INIT_STRUCT_none                /**/
  68 #define INIT_STRUCT_zero                = { }
  69 #define INIT_STRUCT_static_partial      = { .two = 0, }
  70 #define INIT_STRUCT_static_all          = { .one = 0,                   \
  71                                             .two = 0,                   \
  72                                             .three = 0,                 \
  73                                             .four = 0,                  \
  74                                         }
  75 #define INIT_STRUCT_dynamic_partial     = { .two = arg->two, }
  76 #define INIT_STRUCT_dynamic_all         = { .one = arg->one,            \
  77                                             .two = arg->two,            \
  78                                             .three = arg->three,        \
  79                                             .four = arg->four,          \
  80                                         }
  81 #define INIT_STRUCT_runtime_partial     ;                               \
  82                                         var.two = 0
  83 #define INIT_STRUCT_runtime_all         ;                               \
  84                                         var.one = 0;                    \
  85                                         var.two = 0;                    \
  86                                         var.three = 0;                  \
  87                                         var.four = 0
  88
  89 /*
  90  * @name: unique string name for the test
  91  * @var_type: type to be tested for zeroing initialization
  92  * @which: is this a SCALAR, STRING, or STRUCT type?
  93  * @init_level: what kind of initialization is performed
  94  * @xfail: is this test expected to fail?
  95  */
  96 #define DEFINE_TEST_DRIVER(name, var_type, which, xfail)        \
  97 /* Returns 0 on success, 1 on failure. */                       \
  98 static noinline __init int test_ ## name (void)                 \
  99 {                                                               \
 100         var_type zero INIT_CLONE_ ## which;                     \
 101         int ignored;                                            \
 102         u8 sum = 0, i;                                          \
 103                                                                 \
 104         /* Notice when a new test is larger than expected. */   \
 105         BUILD_BUG_ON(sizeof(zero) > MAX_VAR_SIZE);              \
 106                                                                 \
 107         /* Fill clone type with zero for per-field init. */     \
 108         memset(&zero, 0x00, sizeof(zero));                      \
 109         /* Clear entire check buffer for 0xFF overlap test. */  \
 110         memset(check_buf, 0x00, sizeof(check_buf));             \
 111         /* Fill stack with 0xFF. */                             \
 112         ignored = leaf_ ##name((unsigned long)&ignored, 1,      \
 113                                 FETCH_ARG_ ## which(zero));     \
 114         /* Verify all bytes overwritten with 0xFF. */           \
 115         for (sum = 0, i = 0; i < target_size; i++)              \
 116                 sum += (check_buf[i] != 0xFF);                  \
 117         if (sum) {                                              \
 118                 pr_err(#name ": leaf fill was not 0xFF!?\n");   \
 119                 return 1;                                       \
 120         }                                                       \
 121         /* Clear entire check buffer for later bit tests. */    \
 122         memset(check_buf, 0x00, sizeof(check_buf));             \
 123         /* Extract stack-defined variable contents. */          \
 124         ignored = leaf_ ##name((unsigned long)&ignored, 0,      \
 125                                 FETCH_ARG_ ## which(zero));     \
 126                                                                 \
 127         /* Validate that compiler lined up fill and target. */  \
 128         if (!range_contains(fill_start, fill_size,              \
 129                             target_start, target_size)) {       \
 130                 pr_err(#name ": stack fill missed target!?\n"); \
 131                 pr_err(#name ": fill %zu wide\n", fill_size);   \
 132                 pr_err(#name ": target offset by %d\n", \
 133                         (int)((ssize_t)(uintptr_t)fill_start -  \
 134                         (ssize_t)(uintptr_t)target_start));     \
 135                 return 1;                                       \
 136         }                                                       \
 137                                                                 \
 138         /* Look for any bytes still 0xFF in check region. */    \
 139         for (sum = 0, i = 0; i < target_size; i++)              \
 140                 sum += (check_buf[i] == 0xFF);                  \
 141                                                                 \
 142         if (sum == 0) {                                         \
 143                 pr_info(#name " ok\n");                         \
 144                 return 0;                                       \
 145         } else {                                                \
 146                 pr_warn(#name " %sFAIL (uninit bytes: %d)\n",   \
 147                         (xfail) ? "X" : "", sum);               \
 148                 return (xfail) ? 0 : 1;                         \
 149         }                                                       \
 150 }
 151 #define DEFINE_TEST(name, var_type, which, init_level)          \
 152 /* no-op to force compiler into ignoring "uninitialized" vars */\
 153 static noinline __init DO_NOTHING_TYPE_ ## which(var_type)      \
 154 do_nothing_ ## name(var_type *ptr)                              \
 155 {                                                               \
 156         /* Will always be true, but compiler doesn't know. */   \
 157         if ((unsigned long)ptr > 0x2)                           \
 158                 return DO_NOTHING_RETURN_ ## which(ptr);        \
 159         else                                                    \
 160                 return DO_NOTHING_RETURN_ ## which(ptr + 1);    \
 161 }                                                               \
 162 static noinline __init int leaf_ ## name(unsigned long sp,      \
 163                                          bool fill,             \
 164                                          var_type *arg)         \
 165 {                                                               \
 166         char buf[VAR_BUFFER];                                   \
 167         var_type var INIT_ ## which ## _ ## init_level;         \
 168                                                                 \
 169         target_start = &var;                                    \
 170         target_size = sizeof(var);                              \
 171         /*                                                      \
 172          * Keep this buffer around to make sure we've got a     \
 173          * stack frame of SOME kind...                          \
 174          */                                                     \
 175         memset(buf, (char)(sp & 0xff), sizeof(buf));            \
 176         /* Fill variable with 0xFF. */                          \
 177         if (fill) {                                             \
 178                 fill_start = &var;                              \
 179                 fill_size = sizeof(var);                        \
 180                 memset(fill_start,                              \
 181                        (char)((sp & 0xff) | forced_mask),       \
 182                        fill_size);                              \
 183         }                                                       \
 184                                                                 \
 185         /* Silence "never initialized" warnings. */             \
 186         DO_NOTHING_CALL_ ## which(var, name);                   \
 187                                                                 \
 188         /* Exfiltrate "var". */                                 \
 189         memcpy(check_buf, target_start, target_size);           \
 190                                                                 \
 191         return (int)buf[0] | (int)buf[sizeof(buf) - 1];         \
 192 }                                                               \
 193 DEFINE_TEST_DRIVER(name, var_type, which, 0)
 194
 195 /* Structure with no padding. */
 196 struct test_packed {
 197         unsigned long one;
 198         unsigned long two;
 199         unsigned long three;
 200         unsigned long four;
 201 };
 202
 203 /* Simple structure with padding likely to be covered by compiler. */
 204 struct test_small_hole {
 205         size_t one;
 206         char two;
 207         /* 3 byte padding hole here. */
 208         int three;
 209         unsigned long four;
 210 };
 211
 212 /* Trigger unhandled padding in a structure. */
 213 struct test_big_hole {
 214         u8 one;
 215         u8 two;
 216         u8 three;
 217         /* 61 byte padding hole here. */
 218         u8 four __aligned(64);
 219 } __aligned(64);
 220
 221 struct test_trailing_hole {
 222         char *one;
 223         char *two;
 224         char *three;
 225         char four;
 226         /* "sizeof(unsigned long) - 1" byte padding hole here. */
 227 };
 228
 229 /* Test if STRUCTLEAK is clearing structs with __user fields. */
 230 struct test_user {
 231         u8 one;
 232         unsigned long two;
 233         char __user *three;
 234         unsigned long four;
 235 };
 236
 237 #define DEFINE_SCALAR_TEST(name, init)                          \
 238                 DEFINE_TEST(name ## _ ## init, name, SCALAR, init)
 239
 240 #define DEFINE_SCALAR_TESTS(init)                               \
 241                 DEFINE_SCALAR_TEST(u8, init);                   \
 242                 DEFINE_SCALAR_TEST(u16, init);                  \
 243                 DEFINE_SCALAR_TEST(u32, init);                  \
 244                 DEFINE_SCALAR_TEST(u64, init);                  \
 245                 DEFINE_TEST(char_array_ ## init, unsigned char, STRING, init)
 246
 247 #define DEFINE_STRUCT_TEST(name, init)                          \
 248                 DEFINE_TEST(name ## _ ## init,                  \
 249                             struct test_ ## name, STRUCT, init)
 250
 251 #define DEFINE_STRUCT_TESTS(init)                               \
 252                 DEFINE_STRUCT_TEST(small_hole, init);           \
 253                 DEFINE_STRUCT_TEST(big_hole, init);             \
 254                 DEFINE_STRUCT_TEST(trailing_hole, init);        \
 255                 DEFINE_STRUCT_TEST(packed, init)
 256
 257 /* These should be fully initialized all the time! */
 258 DEFINE_SCALAR_TESTS(zero);
 259 DEFINE_STRUCT_TESTS(zero);
 260 /* Static initialization: padding may be left uninitialized. */
 261 DEFINE_STRUCT_TESTS(static_partial);
 262 DEFINE_STRUCT_TESTS(static_all);
 263 /* Dynamic initialization: padding may be left uninitialized. */
 264 DEFINE_STRUCT_TESTS(dynamic_partial);
 265 DEFINE_STRUCT_TESTS(dynamic_all);
 266 /* Runtime initialization: padding may be left uninitialized. */
 267 DEFINE_STRUCT_TESTS(runtime_partial);
 268 DEFINE_STRUCT_TESTS(runtime_all);
 269 /* No initialization without compiler instrumentation. */
 270 DEFINE_SCALAR_TESTS(none);
 271 DEFINE_STRUCT_TESTS(none);
 272 DEFINE_TEST(user, struct test_user, STRUCT, none);
 273
 274 /*
 275  * Check two uses through a variable declaration outside either path,
 276  * which was noticed as a special case in porting earlier stack init
 277  * compiler logic.
 278  */
 279 static int noinline __leaf_switch_none(int path, bool fill)
 280 {
 281         switch (path) {
 282                 uint64_t var;
 283
 284         case 1:
 285                 target_start = &var;
 286                 target_size = sizeof(var);
 287                 if (fill) {
 288                         fill_start = &var;
 289                         fill_size = sizeof(var);
 290
 291                         memset(fill_start, forced_mask | 0x55, fill_size);
 292                 }
 293                 memcpy(check_buf, target_start, target_size);
 294                 break;
 295         case 2:
 296                 target_start = &var;
 297                 target_size = sizeof(var);
 298                 if (fill) {
 299                         fill_start = &var;
 300                         fill_size = sizeof(var);
 301
 302                         memset(fill_start, forced_mask | 0xaa, fill_size);
 303                 }
 304                 memcpy(check_buf, target_start, target_size);
 305                 break;
 306         default:
 307                 var = 5;
 308                 return var & forced_mask;
 309         }
 310         return 0;
 311 }
 312
 313 static noinline __init int leaf_switch_1_none(unsigned long sp, bool fill,
 314                                               uint64_t *arg)
 315 {
 316         return __leaf_switch_none(1, fill);
 317 }
 318
 319 static noinline __init int leaf_switch_2_none(unsigned long sp, bool fill,
 320                                               uint64_t *arg)
 321 {
 322         return __leaf_switch_none(2, fill);
 323 }
 324
 325 /*
 326  * These are expected to fail for most configurations because neither
 327  * GCC nor Clang have a way to perform initialization of variables in
 328  * non-code areas (i.e. in a switch statement before the first "case").
 329  * https://bugs.llvm.org/show_bug.cgi?id=44916
 330  */
 331 DEFINE_TEST_DRIVER(switch_1_none, uint64_t, SCALAR, 1);
 332 DEFINE_TEST_DRIVER(switch_2_none, uint64_t, SCALAR, 1);
 333
 334 static int __init test_stackinit_init(void)
 335 {
 336         unsigned int failures = 0;
 337
 338 #define test_scalars(init)      do {                            \
 339                 failures += test_u8_ ## init ();                \
 340                 failures += test_u16_ ## init ();               \
 341                 failures += test_u32_ ## init ();               \
 342                 failures += test_u64_ ## init ();               \
 343                 failures += test_char_array_ ## init ();        \
 344         } while (0)
 345
 346 #define test_structs(init)      do {                            \
 347                 failures += test_small_hole_ ## init ();        \
 348                 failures += test_big_hole_ ## init ();          \
 349                 failures += test_trailing_hole_ ## init ();     \
 350                 failures += test_packed_ ## init ();            \
 351         } while (0)
 352
 353         /* These are explicitly initialized and should always pass. */
 354         test_scalars(zero);
 355         test_structs(zero);
 356         /* Padding here appears to be accidentally always initialized? */
 357         test_structs(dynamic_partial);
 358         /* Padding initialization depends on compiler behaviors. */
 359         test_structs(static_partial);
 360         test_structs(static_all);
 361         test_structs(dynamic_all);
 362         test_structs(runtime_partial);
 363         test_structs(runtime_all);
 364
 365         /* STRUCTLEAK_BYREF_ALL should cover everything from here down. */
 366         test_scalars(none);
 367         failures += test_switch_1_none();
 368         failures += test_switch_2_none();
 369
 370         /* STRUCTLEAK_BYREF should cover from here down. */
 371         test_structs(none);
 372
 373         /* STRUCTLEAK will only cover this. */
 374         failures += test_user();
 375
 376         if (failures == 0)
 377                 pr_info("all tests passed!\n");
 378         else
 379                 pr_err("failures: %u\n", failures);
 380
 381         return failures ? -EINVAL : 0;
 382 }
 383 module_init(test_stackinit_init);
 384
 385 static void __exit test_stackinit_exit(void)
 386 { }
 387 module_exit(test_stackinit_exit);
 388
 389 MODULE_LICENSE("GPL");