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 = arg->one,            \
  71                                             .two = arg->two,            \
  72                                             .three = arg->three,        \
  73                                             .four = arg->four,          \
  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                                         memset(&var.four, 0,            \
  88                                                sizeof(var.four))
  89
  90 /*
  91  * @name: unique string name for the test
  92  * @var_type: type to be tested for zeroing initialization
  93  * @which: is this a SCALAR, STRING, or STRUCT type?
  94  * @init_level: what kind of initialization is performed
  95  * @xfail: is this test expected to fail?
  96  */
  97 #define DEFINE_TEST_DRIVER(name, var_type, which, xfail)        \
  98 /* Returns 0 on success, 1 on failure. */                       \
  99 static noinline __init int test_ ## name (void)                 \
 100 {                                                               \
 101         var_type zero INIT_CLONE_ ## which;                     \
 102         int ignored;                                            \
 103         u8 sum = 0, i;                                          \
 104                                                                 \
 105         /* Notice when a new test is larger than expected. */   \
 106         BUILD_BUG_ON(sizeof(zero) > MAX_VAR_SIZE);              \
 107                                                                 \
 108         /* Fill clone type with zero for per-field init. */     \
 109         memset(&zero, 0x00, sizeof(zero));                      \
 110         /* Clear entire check buffer for 0xFF overlap test. */  \
 111         memset(check_buf, 0x00, sizeof(check_buf));             \
 112         /* Fill stack with 0xFF. */                             \
 113         ignored = leaf_ ##name((unsigned long)&ignored, 1,      \
 114                                 FETCH_ARG_ ## which(zero));     \
 115         /* Verify all bytes overwritten with 0xFF. */           \
 116         for (sum = 0, i = 0; i < target_size; i++)              \
 117                 sum += (check_buf[i] != 0xFF);                  \
 118         if (sum) {                                              \
 119                 pr_err(#name ": leaf fill was not 0xFF!?\n");   \
 120                 return 1;                                       \
 121         }                                                       \
 122         /* Clear entire check buffer for later bit tests. */    \
 123         memset(check_buf, 0x00, sizeof(check_buf));             \
 124         /* Extract stack-defined variable contents. */          \
 125         ignored = leaf_ ##name((unsigned long)&ignored, 0,      \
 126                                 FETCH_ARG_ ## which(zero));     \
 127                                                                 \
 128         /* Validate that compiler lined up fill and target. */  \
 129         if (!range_contains(fill_start, fill_size,              \
 130                             target_start, target_size)) {       \
 131                 pr_err(#name ": stack fill missed target!?\n"); \
 132                 pr_err(#name ": fill %zu wide\n", fill_size);   \
 133                 pr_err(#name ": target offset by %d\n", \
 134                         (int)((ssize_t)(uintptr_t)fill_start -  \
 135                         (ssize_t)(uintptr_t)target_start));     \
 136                 return 1;                                       \
 137         }                                                       \
 138                                                                 \
 139         /* Look for any bytes still 0xFF in check region. */    \
 140         for (sum = 0, i = 0; i < target_size; i++)              \
 141                 sum += (check_buf[i] == 0xFF);                  \
 142                                                                 \
 143         if (sum == 0) {                                         \
 144                 pr_info(#name " ok\n");                         \
 145                 return 0;                                       \
 146         } else {                                                \
 147                 pr_warn(#name " %sFAIL (uninit bytes: %d)\n",   \
 148                         (xfail) ? "X" : "", sum);               \
 149                 return (xfail) ? 0 : 1;                         \
 150         }                                                       \
 151 }
 152 #define DEFINE_TEST(name, var_type, which, init_level)          \
 153 /* no-op to force compiler into ignoring "uninitialized" vars */\
 154 static noinline __init DO_NOTHING_TYPE_ ## which(var_type)      \
 155 do_nothing_ ## name(var_type *ptr)                              \
 156 {                                                               \
 157         /* Will always be true, but compiler doesn't know. */   \
 158         if ((unsigned long)ptr > 0x2)                           \
 159                 return DO_NOTHING_RETURN_ ## which(ptr);        \
 160         else                                                    \
 161                 return DO_NOTHING_RETURN_ ## which(ptr + 1);    \
 162 }                                                               \
 163 static noinline __init int leaf_ ## name(unsigned long sp,      \
 164                                          bool fill,             \
 165                                          var_type *arg)         \
 166 {                                                               \
 167         char buf[VAR_BUFFER];                                   \
 168         var_type var INIT_ ## which ## _ ## init_level;         \
 169                                                                 \
 170         target_start = &var;                                    \
 171         target_size = sizeof(var);                              \
 172         /*                                                      \
 173          * Keep this buffer around to make sure we've got a     \
 174          * stack frame of SOME kind...                          \
 175          */                                                     \
 176         memset(buf, (char)(sp & 0xff), sizeof(buf));            \
 177         /* Fill variable with 0xFF. */                          \
 178         if (fill) {                                             \
 179                 fill_start = &var;                              \
 180                 fill_size = sizeof(var);                        \
 181                 memset(fill_start,                              \
 182                        (char)((sp & 0xff) | forced_mask),       \
 183                        fill_size);                              \
 184         }                                                       \
 185                                                                 \
 186         /* Silence "never initialized" warnings. */             \
 187         DO_NOTHING_CALL_ ## which(var, name);                   \
 188                                                                 \
 189         /* Exfiltrate "var". */                                 \
 190         memcpy(check_buf, target_start, target_size);           \
 191                                                                 \
 192         return (int)buf[0] | (int)buf[sizeof(buf) - 1];         \
 193 }                                                               \
 194 DEFINE_TEST_DRIVER(name, var_type, which, 0)
 195
 196 /* Structure with no padding. */
 197 struct test_packed {
 198         unsigned long one;
 199         unsigned long two;
 200         unsigned long three;
 201         unsigned long four;
 202 };
 203
 204 /* Simple structure with padding likely to be covered by compiler. */
 205 struct test_small_hole {
 206         size_t one;
 207         char two;
 208         /* 3 byte padding hole here. */
 209         int three;
 210         unsigned long four;
 211 };
 212
 213 /* Try to trigger unhandled padding in a structure. */
 214 struct test_aligned {
 215         u32 internal1;
 216         u64 internal2;
 217 } __aligned(64);
 218
 219 struct test_big_hole {
 220         u8 one;
 221         u8 two;
 222         u8 three;
 223         /* 61 byte padding hole here. */
 224         struct test_aligned four;
 225 } __aligned(64);
 226
 227 struct test_trailing_hole {
 228         char *one;
 229         char *two;
 230         char *three;
 231         char four;
 232         /* "sizeof(unsigned long) - 1" byte padding hole here. */
 233 };
 234
 235 /* Test if STRUCTLEAK is clearing structs with __user fields. */
 236 struct test_user {
 237         u8 one;
 238         unsigned long two;
 239         char __user *three;
 240         unsigned long four;
 241 };
 242
 243 #define DEFINE_SCALAR_TEST(name, init)                          \
 244                 DEFINE_TEST(name ## _ ## init, name, SCALAR, init)
 245
 246 #define DEFINE_SCALAR_TESTS(init)                               \
 247                 DEFINE_SCALAR_TEST(u8, init);                   \
 248                 DEFINE_SCALAR_TEST(u16, init);                  \
 249                 DEFINE_SCALAR_TEST(u32, init);                  \
 250                 DEFINE_SCALAR_TEST(u64, init);                  \
 251                 DEFINE_TEST(char_array_ ## init, unsigned char, STRING, init)
 252
 253 #define DEFINE_STRUCT_TEST(name, init)                          \
 254                 DEFINE_TEST(name ## _ ## init,                  \
 255                             struct test_ ## name, STRUCT, init)
 256
 257 #define DEFINE_STRUCT_TESTS(init)                               \
 258                 DEFINE_STRUCT_TEST(small_hole, init);           \
 259                 DEFINE_STRUCT_TEST(big_hole, init);             \
 260                 DEFINE_STRUCT_TEST(trailing_hole, init);        \
 261                 DEFINE_STRUCT_TEST(packed, init)
 262
 263 /* These should be fully initialized all the time! */
 264 DEFINE_SCALAR_TESTS(zero);
 265 DEFINE_STRUCT_TESTS(zero);
 266 /* Static initialization: padding may be left uninitialized. */
 267 DEFINE_STRUCT_TESTS(static_partial);
 268 DEFINE_STRUCT_TESTS(static_all);
 269 /* Dynamic initialization: padding may be left uninitialized. */
 270 DEFINE_STRUCT_TESTS(dynamic_partial);
 271 DEFINE_STRUCT_TESTS(dynamic_all);
 272 /* Runtime initialization: padding may be left uninitialized. */
 273 DEFINE_STRUCT_TESTS(runtime_partial);
 274 DEFINE_STRUCT_TESTS(runtime_all);
 275 /* No initialization without compiler instrumentation. */
 276 DEFINE_SCALAR_TESTS(none);
 277 DEFINE_STRUCT_TESTS(none);
 278 DEFINE_TEST(user, struct test_user, STRUCT, none);
 279
 280 /*
 281  * Check two uses through a variable declaration outside either path,
 282  * which was noticed as a special case in porting earlier stack init
 283  * compiler logic.
 284  */
 285 static int noinline __leaf_switch_none(int path, bool fill)
 286 {
 287         switch (path) {
 288                 uint64_t var;
 289
 290         case 1:
 291                 target_start = &var;
 292                 target_size = sizeof(var);
 293                 if (fill) {
 294                         fill_start = &var;
 295                         fill_size = sizeof(var);
 296
 297                         memset(fill_start, forced_mask | 0x55, fill_size);
 298                 }
 299                 memcpy(check_buf, target_start, target_size);
 300                 break;
 301         case 2:
 302                 target_start = &var;
 303                 target_size = sizeof(var);
 304                 if (fill) {
 305                         fill_start = &var;
 306                         fill_size = sizeof(var);
 307
 308                         memset(fill_start, forced_mask | 0xaa, fill_size);
 309                 }
 310                 memcpy(check_buf, target_start, target_size);
 311                 break;
 312         default:
 313                 var = 5;
 314                 return var & forced_mask;
 315         }
 316         return 0;
 317 }
 318
 319 static noinline __init int leaf_switch_1_none(unsigned long sp, bool fill,
 320                                               uint64_t *arg)
 321 {
 322         return __leaf_switch_none(1, fill);
 323 }
 324
 325 static noinline __init int leaf_switch_2_none(unsigned long sp, bool fill,
 326                                               uint64_t *arg)
 327 {
 328         return __leaf_switch_none(2, fill);
 329 }
 330
 331 /*
 332  * These are expected to fail for most configurations because neither
 333  * GCC nor Clang have a way to perform initialization of variables in
 334  * non-code areas (i.e. in a switch statement before the first "case").
 335  * https://bugs.llvm.org/show_bug.cgi?id=44916
 336  */
 337 DEFINE_TEST_DRIVER(switch_1_none, uint64_t, SCALAR, 1);
 338 DEFINE_TEST_DRIVER(switch_2_none, uint64_t, SCALAR, 1);
 339
 340 static int __init test_stackinit_init(void)
 341 {
 342         unsigned int failures = 0;
 343
 344 #define test_scalars(init)      do {                            \
 345                 failures += test_u8_ ## init ();                \
 346                 failures += test_u16_ ## init ();               \
 347                 failures += test_u32_ ## init ();               \
 348                 failures += test_u64_ ## init ();               \
 349                 failures += test_char_array_ ## init ();        \
 350         } while (0)
 351
 352 #define test_structs(init)      do {                            \
 353                 failures += test_small_hole_ ## init ();        \
 354                 failures += test_big_hole_ ## init ();          \
 355                 failures += test_trailing_hole_ ## init ();     \
 356                 failures += test_packed_ ## init ();            \
 357         } while (0)
 358
 359         /* These are explicitly initialized and should always pass. */
 360         test_scalars(zero);
 361         test_structs(zero);
 362         /* Padding here appears to be accidentally always initialized? */
 363         test_structs(dynamic_partial);
 364         /* Padding initialization depends on compiler behaviors. */
 365         test_structs(static_partial);
 366         test_structs(static_all);
 367         test_structs(dynamic_all);
 368         test_structs(runtime_partial);
 369         test_structs(runtime_all);
 370
 371         /* STRUCTLEAK_BYREF_ALL should cover everything from here down. */
 372         test_scalars(none);
 373         failures += test_switch_1_none();
 374         failures += test_switch_2_none();
 375
 376         /* STRUCTLEAK_BYREF should cover from here down. */
 377         test_structs(none);
 378
 379         /* STRUCTLEAK will only cover this. */
 380         failures += test_user();
 381
 382         if (failures == 0)
 383                 pr_info("all tests passed!\n");
 384         else
 385                 pr_err("failures: %u\n", failures);
 386
 387         return failures ? -EINVAL : 0;
 388 }
 389 module_init(test_stackinit_init);
 390
 391 static void __exit test_stackinit_exit(void)
 392 { }
 393 module_exit(test_stackinit_exit);
 394
 395 MODULE_LICENSE("GPL");