san/kasan-fakestack.c

   1 /*
   2  * Copyright (c) 2016 Apple Inc. All rights reserved.
   3  *
   4  * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
   5  *
   6  * This file contains Original Code and/or Modifications of Original Code
   7  * as defined in and that are subject to the Apple Public Source License
   8  * Version 2.0 (the 'License'). You may not use this file except in
   9  * compliance with the License. The rights granted to you under the License
  10  * may not be used to create, or enable the creation or redistribution of,
  11  * unlawful or unlicensed copies of an Apple operating system, or to
  12  * circumvent, violate, or enable the circumvention or violation of, any
  13  * terms of an Apple operating system software license agreement.
  14  *
  15  * Please obtain a copy of the License at
  16  * http://www.opensource.apple.com/apsl/ and read it before using this file.
  17  *
  18  * The Original Code and all software distributed under the License are
  19  * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
  20  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
  21  * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
  22  * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
  23  * Please see the License for the specific language governing rights and
  24  * limitations under the License.
  25  *
  26  * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
  27  */
  28
  29 #include <stdint.h>
  30 #include <stdbool.h>
  31 #include <kern/assert.h>
  32 #include <kern/zalloc.h>
  33 #include <mach/mach_vm.h>
  34 #include <mach/vm_param.h>
  35 #include <libkern/libkern.h>
  36 #include <libkern/OSAtomic.h>
  37 #include <sys/queue.h>
  38 #include <kern/thread.h>
  39 #include <kern/debug.h>
  40
  41 #include <kasan.h>
  42 #include <kasan_internal.h>
  43
  44 int __asan_option_detect_stack_use_after_return = 0;
  45 int fakestack_enabled = 0;
  46
  47 #define FAKESTACK_HEADER_SZ 64
  48 #define FAKESTACK_NUM_SZCLASS 7
  49
  50 #define FAKESTACK_FREED     0 /* forced by clang */
  51 #define FAKESTACK_ALLOCATED 1
  52
  53 #if FAKESTACK
  54
  55 struct fakestack_header {
  56         LIST_ENTRY(fakestack_header) list;
  57         void *site; /* allocation site */
  58         struct {
  59                 uint8_t flag;
  60                 vm_size_t realsz : 52;
  61                 vm_size_t sz_class : 4;
  62         };
  63         uint64_t __pad0;
  64 };
  65 _Static_assert(sizeof(struct fakestack_header) <= FAKESTACK_HEADER_SZ, "fakestack_header size mismatch");
  66
  67 static zone_t fakestack_zones[FAKESTACK_NUM_SZCLASS];
  68 static char fakestack_names[FAKESTACK_NUM_SZCLASS][16];
  69 static const unsigned long fakestack_min = 1 << 6;
  70 static const unsigned long __unused fakestack_max = 1 << 16;
  71
  72 /*
  73  * Enter a fakestack critical section in a reentrant-safe fashion. Returns true on
  74  * success with the kasan lock held.
  75  */
  76 static bool
  77 thread_enter_fakestack(boolean_t *flags)
  78 {
  79         thread_t cur = current_thread();
  80         if (cur && kasan_lock_held(cur)) {
  81                 /* current thread is already in kasan - fail */
  82                 return false;
  83         }
  84         kasan_lock(flags);
  85         return true;
  86 }
  87
  88 static volatile long suspend_count;
  89 static const long suspend_threshold = 20;
  90
  91 void
  92 kasan_fakestack_suspend(void)
  93 {
  94         if (OSIncrementAtomicLong(&suspend_count) == suspend_threshold) {
  95                 __asan_option_detect_stack_use_after_return = 0;
  96         }
  97 }
  98
  99 void
 100 kasan_fakestack_resume(void)
 101 {
 102         long orig = OSDecrementAtomicLong(&suspend_count);
 103         assert(orig >= 0);
 104
 105         if (fakestack_enabled && orig == suspend_threshold) {
 106                 __asan_option_detect_stack_use_after_return = 1;
 107         }
 108 }
 109
 110 static bool
 111 ptr_is_on_stack(uptr ptr)
 112 {
 113         vm_offset_t base = dtrace_get_kernel_stack(current_thread());
 114
 115         if (ptr >= base && ptr < (base + kernel_stack_size)) {
 116                 return true;
 117         } else {
 118                 return false;
 119         }
 120 }
 121
 122 /* free all unused fakestack entries */
 123 static void NOINLINE
 124 kasan_fakestack_gc(thread_t thread)
 125 {
 126         struct fakestack_header *cur, *tmp;
 127         LIST_HEAD(, fakestack_header) tofree = LIST_HEAD_INITIALIZER(tofree);
 128
 129         /* move all the freed elements off the main list */
 130         struct fakestack_header_list *head = &kasan_get_thread_data(thread)->fakestack_head;
 131         LIST_FOREACH_SAFE(cur, head, list, tmp) {
 132                 if (cur->flag == FAKESTACK_FREED) {
 133                         LIST_REMOVE(cur, list);
 134                         LIST_INSERT_HEAD(&tofree, cur, list);
 135                 }
 136         }
 137
 138         /* ... then actually free them */
 139         LIST_FOREACH_SAFE(cur, &tofree, list, tmp) {
 140                 zone_t zone = fakestack_zones[cur->sz_class];
 141                 size_t sz = (fakestack_min << cur->sz_class) + FAKESTACK_HEADER_SZ;
 142                 LIST_REMOVE(cur, list);
 143
 144                 void *ptr = (void *)cur;
 145                 kasan_free_internal(&ptr, &sz, KASAN_HEAP_FAKESTACK, &zone, cur->realsz, 1, FAKESTACK_QUARANTINE);
 146                 if (ptr) {
 147                         zfree(zone, ptr);
 148                 }
 149         }
 150 }
 151
 152 static uint8_t **
 153 fakestack_flag_ptr(vm_offset_t ptr, vm_size_t sz)
 154 {
 155         uint8_t **x = (uint8_t **)ptr;
 156         size_t idx = sz / 8;
 157         return &x[idx - 1];
 158 }
 159
 160 static uptr ALWAYS_INLINE
 161 kasan_fakestack_alloc(int sz_class, size_t realsz)
 162 {
 163         if (!__asan_option_detect_stack_use_after_return) {
 164                 return 0;
 165         }
 166
 167         if (sz_class >= FAKESTACK_NUM_SZCLASS) {
 168                 return 0;
 169         }
 170
 171         uptr ret = 0;
 172         size_t sz = fakestack_min << sz_class;
 173         assert(realsz <= sz);
 174         assert(sz <= fakestack_max);
 175         zone_t zone = fakestack_zones[sz_class];
 176
 177         boolean_t flags;
 178         if (!thread_enter_fakestack(&flags)) {
 179                 return 0;
 180         }
 181
 182         kasan_fakestack_gc(current_thread()); /* XXX: optimal? */
 183
 184         ret = (uptr)zget(zone);
 185
 186         if (ret) {
 187                 size_t leftrz = 32 + FAKESTACK_HEADER_SZ;
 188                 size_t validsz = realsz - 32 - 16; /* remove redzones */
 189                 size_t rightrz = sz - validsz - 32; /* 16 bytes, plus whatever is left over */
 190                 struct fakestack_header *hdr = (struct fakestack_header *)ret;
 191
 192                 kasan_poison(ret, validsz, leftrz, rightrz, ASAN_STACK_RZ);
 193
 194                 hdr->site = __builtin_return_address(0);
 195                 hdr->realsz = realsz;
 196                 hdr->sz_class = sz_class;
 197                 hdr->flag = FAKESTACK_ALLOCATED;
 198                 ret += FAKESTACK_HEADER_SZ;
 199
 200                 *fakestack_flag_ptr(ret, sz) = &hdr->flag; /* back ptr to the slot */
 201                 struct fakestack_header_list *head = &kasan_get_thread_data(current_thread())->fakestack_head;
 202                 LIST_INSERT_HEAD(head, hdr, list);
 203         }
 204
 205         kasan_unlock(flags);
 206         return ret;
 207 }
 208
 209 static void NOINLINE
 210 kasan_fakestack_free(int sz_class, uptr dst, size_t realsz)
 211 {
 212         if (ptr_is_on_stack(dst)) {
 213                 return;
 214         }
 215
 216         assert(realsz <= (fakestack_min << sz_class));
 217
 218         vm_size_t sz = fakestack_min << sz_class;
 219         zone_t zone = fakestack_zones[sz_class];
 220         assert(zone);
 221
 222         /* TODO: check the magic? */
 223
 224         dst -= FAKESTACK_HEADER_SZ;
 225         sz += FAKESTACK_HEADER_SZ;
 226
 227         struct fakestack_header *hdr = (struct fakestack_header *)dst;
 228         assert(hdr->sz_class == sz_class);
 229
 230         boolean_t flags;
 231         kasan_lock(&flags);
 232
 233         LIST_REMOVE(hdr, list);
 234
 235         kasan_free_internal((void **)&dst, &sz, KASAN_HEAP_FAKESTACK, &zone, realsz, 1, FAKESTACK_QUARANTINE);
 236         if (dst) {
 237                 zfree(zone, (void *)dst);
 238         }
 239
 240         kasan_unlock(flags);
 241 }
 242
 243 void NOINLINE
 244 kasan_unpoison_fakestack(thread_t thread)
 245 {
 246         boolean_t flags;
 247         if (!thread_enter_fakestack(&flags)) {
 248                 panic("expected success entering fakestack\n");
 249         }
 250
 251         struct fakestack_header_list *head = &kasan_get_thread_data(thread)->fakestack_head;
 252         struct fakestack_header *cur;
 253         LIST_FOREACH(cur, head, list) {
 254                 if (cur->flag == FAKESTACK_ALLOCATED) {
 255                         cur->flag = FAKESTACK_FREED;
 256                 }
 257         }
 258
 259         kasan_fakestack_gc(thread);
 260         kasan_unlock(flags);
 261 }
 262
 263 void NOINLINE
 264 kasan_init_fakestack(void)
 265 {
 266         /* allocate the fakestack zones */
 267         for (int i = 0; i < FAKESTACK_NUM_SZCLASS; i++) {
 268                 zone_t z;
 269                 unsigned long sz = (fakestack_min << i) + FAKESTACK_HEADER_SZ;
 270                 size_t maxsz = 256UL * 1024;
 271
 272                 if (i <= 3) {
 273                         /* size classes 0..3 are much more common */
 274                         maxsz *= 4;
 275                 }
 276
 277                 snprintf(fakestack_names[i], 16, "fakestack.%d", i);
 278                 z = zinit(sz, maxsz, sz, fakestack_names[i]);
 279                 assert(z);
 280                 zone_change(z, Z_NOCALLOUT, TRUE);
 281                 zone_change(z, Z_EXHAUST, TRUE);
 282                 zone_change(z, Z_EXPAND,  FALSE);
 283                 zone_change(z, Z_COLLECT, FALSE);
 284                 zone_change(z, Z_KASAN_QUARANTINE, FALSE);
 285                 zfill(z, maxsz / sz);
 286                 fakestack_zones[i] = z;
 287         }
 288
 289         /* globally enable */
 290         if (fakestack_enabled) {
 291                 __asan_option_detect_stack_use_after_return = 1;
 292         }
 293 }
 294
 295 #else /* FAKESTACK */
 296
 297 void
 298 kasan_init_fakestack(void)
 299 {
 300         assert(__asan_option_detect_stack_use_after_return == 0);
 301 }
 302
 303 void
 304 kasan_unpoison_fakestack(thread_t __unused thread)
 305 {
 306         assert(__asan_option_detect_stack_use_after_return == 0);
 307 }
 308
 309 static uptr
 310 kasan_fakestack_alloc(int __unused sz_class, size_t __unused realsz)
 311 {
 312         assert(__asan_option_detect_stack_use_after_return == 0);
 313         return 0;
 314 }
 315
 316 static void
 317 kasan_fakestack_free(int __unused sz_class, uptr __unused dst, size_t __unused realsz)
 318 {
 319         assert(__asan_option_detect_stack_use_after_return == 0);
 320         panic("fakestack_free called on non-FAKESTACK config\n");
 321 }
 322
 323 #endif
 324
 325 void kasan_init_thread(struct kasan_thread_data *td)
 326 {
 327         LIST_INIT(&td->fakestack_head);
 328 }
 329
 330 #define FAKESTACK_DECLARE(szclass) \
 331         uptr __asan_stack_malloc_##szclass(size_t sz)  { return kasan_fakestack_alloc(szclass, sz); } \
 332         void __asan_stack_free_##szclass(uptr dst, size_t sz)  { kasan_fakestack_free(szclass, dst, sz); }
 333
 334 FAKESTACK_DECLARE(0)
 335 FAKESTACK_DECLARE(1)
 336 FAKESTACK_DECLARE(2)
 337 FAKESTACK_DECLARE(3)
 338 FAKESTACK_DECLARE(4)
 339 FAKESTACK_DECLARE(5)
 340 FAKESTACK_DECLARE(6)
 341 FAKESTACK_DECLARE(7)
 342 FAKESTACK_DECLARE(8)
 343 FAKESTACK_DECLARE(9)
 344 FAKESTACK_DECLARE(10)