1 /* 2 * Copyright © 2007,2008,2009,2010 Red Hat, Inc. 3 * Copyright © 2012,2018 Google, Inc. 4 * 5 * This is part of HarfBuzz, a text shaping library. 6 * 7 * Permission is hereby granted, without written agreement and without 8 * license or royalty fees, to use, copy, modify, and distribute this 9 * software and its documentation for any purpose, provided that the 10 * above copyright notice and the following two paragraphs appear in 11 * all copies of this software. 12 * 13 * IN NO EVENT SHALL THE COPYRIGHT HOLDER BE LIABLE TO ANY PARTY FOR 14 * DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES 15 * ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION, EVEN 16 * IF THE COPYRIGHT HOLDER HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH 17 * DAMAGE. 18 * 19 * THE COPYRIGHT HOLDER SPECIFICALLY DISCLAIMS ANY WARRANTIES, INCLUDING, 20 * BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND 21 * FITNESS FOR A PARTICULAR PURPOSE. THE SOFTWARE PROVIDED HEREUNDER IS 22 * ON AN "AS IS" BASIS, AND THE COPYRIGHT HOLDER HAS NO OBLIGATION TO 23 * PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS. 24 * 25 * Red Hat Author(s): Behdad Esfahbod 26 * Google Author(s): Behdad Esfahbod 27 */ 28 29 #ifndef HB_SANITIZE_HH 30 #define HB_SANITIZE_HH 31 32 #include "hb.hh" 33 #include "hb-blob.hh" 34 #include "hb-dispatch.hh" 35 36 37 /* 38 * Sanitize 39 * 40 * 41 * === Introduction === 42 * 43 * The sanitize machinery is at the core of our zero-cost font loading. We 44 * mmap() font file into memory and create a blob out of it. Font subtables 45 * are returned as a readonly sub-blob of the main font blob. These table 46 * blobs are then sanitized before use, to ensure invalid memory access does 47 * not happen. The toplevel sanitize API use is like, eg. to load the 'head' 48 * table: 49 * 50 * hb_blob_t *head_blob = hb_sanitize_context_t ().reference_table<OT::head> (face); 51 * 52 * The blob then can be converted to a head table struct with: 53 * 54 * const head *head_table = head_blob->as<head> (); 55 * 56 * What the reference_table does is, to call hb_face_reference_table() to load 57 * the table blob, sanitize it and return either the sanitized blob, or empty 58 * blob if sanitization failed. The blob->as() function returns the null 59 * object of its template type argument if the blob is empty. Otherwise, it 60 * just casts the blob contents to the desired type. 61 * 62 * Sanitizing a blob of data with a type T works as follows (with minor 63 * simplification): 64 * 65 * - Cast blob content to T*, call sanitize() method of it, 66 * - If sanitize succeeded, return blob. 67 * - Otherwise, if blob is not writable, try making it writable, 68 * or copy if cannot be made writable in-place, 69 * - Call sanitize() again. Return blob if sanitize succeeded. 70 * - Return empty blob otherwise. 71 * 72 * 73 * === The sanitize() contract === 74 * 75 * The sanitize() method of each object type shall return true if it's safe to 76 * call other methods of the object, and %false otherwise. 77 * 78 * Note that what sanitize() checks for might align with what the specification 79 * describes as valid table data, but does not have to be. In particular, we 80 * do NOT want to be pedantic and concern ourselves with validity checks that 81 * are irrelevant to our use of the table. On the contrary, we want to be 82 * lenient with error handling and accept invalid data to the extent that it 83 * does not impose extra burden on us. 84 * 85 * Based on the sanitize contract, one can see that what we check for depends 86 * on how we use the data in other table methods. Ie. if other table methods 87 * assume that offsets do NOT point out of the table data block, then that's 88 * something sanitize() must check for (GSUB/GPOS/GDEF/etc work this way). On 89 * the other hand, if other methods do such checks themselves, then sanitize() 90 * does not have to bother with them (glyf/local work this way). The choice 91 * depends on the table structure and sanitize() performance. For example, to 92 * check glyf/loca offsets in sanitize() would cost O(num-glyphs). We try hard 93 * to avoid such costs during font loading. By postponing such checks to the 94 * actual glyph loading, we reduce the sanitize cost to O(1) and total runtime 95 * cost to O(used-glyphs). As such, this is preferred. 96 * 97 * The same argument can be made re GSUB/GPOS/GDEF, but there, the table 98 * structure is so complicated that by checking all offsets at sanitize() time, 99 * we make the code much simpler in other methods, as offsets and referenced 100 * objects do not need to be validated at each use site. 101 */ 102 103 /* This limits sanitizing time on really broken fonts. */ 104 #ifndef HB_SANITIZE_MAX_EDITS 105 #define HB_SANITIZE_MAX_EDITS 32 106 #endif 107 #ifndef HB_SANITIZE_MAX_OPS_FACTOR 108 #define HB_SANITIZE_MAX_OPS_FACTOR 64 109 #endif 110 #ifndef HB_SANITIZE_MAX_OPS_MIN 111 #define HB_SANITIZE_MAX_OPS_MIN 16384 112 #endif 113 #ifndef HB_SANITIZE_MAX_OPS_MAX 114 #define HB_SANITIZE_MAX_OPS_MAX 0x3FFFFFFF 115 #endif 116 #ifndef HB_SANITIZE_MAX_SUBTABLES 117 #define HB_SANITIZE_MAX_SUBTABLES 0x4000 118 #endif 119 120 struct hb_sanitize_context_t : 121 hb_dispatch_context_t<hb_sanitize_context_t, bool, HB_DEBUG_SANITIZE> 122 { hb_sanitize_context_thb_sanitize_context_t123 hb_sanitize_context_t () : 124 start (nullptr), end (nullptr), 125 length (0), 126 max_ops (0), max_subtables (0), 127 recursion_depth (0), 128 writable (false), edit_count (0), 129 blob (nullptr), 130 num_glyphs (65536), 131 num_glyphs_set (false), 132 lazy_some_gpos (false) {} 133 get_namehb_sanitize_context_t134 const char *get_name () { return "SANITIZE"; } 135 template <typename T, typename F> may_dispatchhb_sanitize_context_t136 bool may_dispatch (const T *obj HB_UNUSED, const F *format) 137 { return format->sanitize (this); } default_return_valuehb_sanitize_context_t138 static return_t default_return_value () { return true; } no_dispatch_return_valuehb_sanitize_context_t139 static return_t no_dispatch_return_value () { return false; } stop_sublookup_iterationhb_sanitize_context_t140 bool stop_sublookup_iteration (const return_t r) const { return !r; } 141 visit_subtableshb_sanitize_context_t142 bool visit_subtables (unsigned count) 143 { 144 max_subtables += count; 145 return max_subtables < HB_SANITIZE_MAX_SUBTABLES; 146 } 147 148 private: 149 template <typename T, typename ...Ts> auto 150 _dispatch (const T &obj, hb_priority<1>, Ts&&... ds) HB_AUTO_RETURN 151 ( obj.sanitize (this, std::forward<Ts> (ds)...) ) 152 template <typename T, typename ...Ts> auto 153 _dispatch (const T &obj, hb_priority<0>, Ts&&... ds) HB_AUTO_RETURN 154 ( obj.dispatch (this, std::forward<Ts> (ds)...) ) 155 public: 156 template <typename T, typename ...Ts> auto dispatchhb_sanitize_context_t157 dispatch (const T &obj, Ts&&... ds) HB_AUTO_RETURN 158 ( _dispatch (obj, hb_prioritize, std::forward<Ts> (ds)...) ) 159 160 hb_sanitize_context_t (hb_blob_t *b) : hb_sanitize_context_t () 161 { 162 init (b); 163 164 if (blob) 165 start_processing (); 166 } 167 ~hb_sanitize_context_thb_sanitize_context_t168 ~hb_sanitize_context_t () 169 { 170 if (blob) 171 end_processing (); 172 } 173 inithb_sanitize_context_t174 void init (hb_blob_t *b) 175 { 176 this->blob = hb_blob_reference (b); 177 this->writable = false; 178 } 179 set_num_glyphshb_sanitize_context_t180 void set_num_glyphs (unsigned int num_glyphs_) 181 { 182 num_glyphs = num_glyphs_; 183 num_glyphs_set = true; 184 } get_num_glyphshb_sanitize_context_t185 unsigned int get_num_glyphs () { return num_glyphs; } 186 set_max_opshb_sanitize_context_t187 void set_max_ops (int max_ops_) { max_ops = max_ops_; } 188 189 template <typename T> set_objecthb_sanitize_context_t190 void set_object (const T *obj) 191 { 192 reset_object (); 193 194 if (!obj) return; 195 196 const char *obj_start = (const char *) obj; 197 if (unlikely (obj_start < this->start || this->end <= obj_start)) 198 { 199 this->start = this->end = nullptr; 200 this->length = 0; 201 } 202 else 203 { 204 this->start = obj_start; 205 this->end = obj_start + hb_min (size_t (this->end - obj_start), obj->get_size ()); 206 this->length = this->end - this->start; 207 } 208 } 209 reset_objecthb_sanitize_context_t210 void reset_object () 211 { 212 this->start = this->blob->data; 213 this->end = this->start + this->blob->length; 214 this->length = this->end - this->start; 215 assert (this->start <= this->end); /* Must not overflow. */ 216 } 217 start_processinghb_sanitize_context_t218 void start_processing () 219 { 220 reset_object (); 221 unsigned m; 222 if (unlikely (hb_unsigned_mul_overflows (this->end - this->start, HB_SANITIZE_MAX_OPS_FACTOR, &m))) 223 this->max_ops = HB_SANITIZE_MAX_OPS_MAX; 224 else 225 this->max_ops = hb_clamp (m, 226 (unsigned) HB_SANITIZE_MAX_OPS_MIN, 227 (unsigned) HB_SANITIZE_MAX_OPS_MAX); 228 this->edit_count = 0; 229 this->debug_depth = 0; 230 this->recursion_depth = 0; 231 232 DEBUG_MSG_LEVEL (SANITIZE, start, 0, +1, 233 "start [%p..%p] (%lu bytes)", 234 this->start, this->end, 235 (unsigned long) (this->end - this->start)); 236 } 237 end_processinghb_sanitize_context_t238 void end_processing () 239 { 240 DEBUG_MSG_LEVEL (SANITIZE, this->start, 0, -1, 241 "end [%p..%p] %u edit requests", 242 this->start, this->end, this->edit_count); 243 244 hb_blob_destroy (this->blob); 245 this->blob = nullptr; 246 this->start = this->end = nullptr; 247 this->length = 0; 248 } 249 get_edit_counthb_sanitize_context_t250 unsigned get_edit_count () { return edit_count; } 251 252 check_opshb_sanitize_context_t253 bool check_ops(unsigned count) 254 { 255 /* Avoid underflow */ 256 if (unlikely (this->max_ops < 0 || count >= (unsigned) this->max_ops)) 257 { 258 this->max_ops = -1; 259 return false; 260 } 261 this->max_ops -= (int) count; 262 return true; 263 } 264 265 #ifndef HB_OPTIMIZE_SIZE 266 HB_ALWAYS_INLINE 267 #endif check_rangehb_sanitize_context_t268 bool check_range (const void *base, 269 unsigned int len) const 270 { 271 const char *p = (const char *) base; 272 bool ok = (uintptr_t) (p - this->start) <= this->length && 273 (unsigned int) (this->end - p) >= len && 274 ((this->max_ops -= len) > 0); 275 276 DEBUG_MSG_LEVEL (SANITIZE, p, this->debug_depth+1, 0, 277 "check_range [%p..%p]" 278 " (%u bytes) in [%p..%p] -> %s", 279 p, p + len, len, 280 this->start, this->end, 281 ok ? "OK" : "OUT-OF-RANGE"); 282 283 return likely (ok); 284 } 285 #ifndef HB_OPTIMIZE_SIZE 286 HB_ALWAYS_INLINE 287 #endif check_range_fasthb_sanitize_context_t288 bool check_range_fast (const void *base, 289 unsigned int len) const 290 { 291 const char *p = (const char *) base; 292 bool ok = ((uintptr_t) (p - this->start) <= this->length && 293 (unsigned int) (this->end - p) >= len); 294 295 DEBUG_MSG_LEVEL (SANITIZE, p, this->debug_depth+1, 0, 296 "check_range_fast [%p..%p]" 297 " (%u bytes) in [%p..%p] -> %s", 298 p, p + len, len, 299 this->start, this->end, 300 ok ? "OK" : "OUT-OF-RANGE"); 301 302 return likely (ok); 303 } 304 305 #ifndef HB_OPTIMIZE_SIZE 306 HB_ALWAYS_INLINE 307 #endif check_pointhb_sanitize_context_t308 bool check_point (const void *base) const 309 { 310 const char *p = (const char *) base; 311 bool ok = (uintptr_t) (p - this->start) <= this->length; 312 313 DEBUG_MSG_LEVEL (SANITIZE, p, this->debug_depth+1, 0, 314 "check_point [%p]" 315 " in [%p..%p] -> %s", 316 p, 317 this->start, this->end, 318 ok ? "OK" : "OUT-OF-RANGE"); 319 320 return likely (ok); 321 } 322 323 template <typename T> check_rangehb_sanitize_context_t324 bool check_range (const T *base, 325 unsigned int a, 326 unsigned int b) const 327 { 328 unsigned m; 329 return !hb_unsigned_mul_overflows (a, b, &m) && 330 this->check_range (base, m); 331 } 332 333 template <typename T> check_rangehb_sanitize_context_t334 bool check_range (const T *base, 335 unsigned int a, 336 unsigned int b, 337 unsigned int c) const 338 { 339 unsigned m; 340 return !hb_unsigned_mul_overflows (a, b, &m) && 341 this->check_range (base, m, c); 342 } 343 344 template <typename T> 345 HB_ALWAYS_INLINE check_array_sizedhb_sanitize_context_t346 bool check_array_sized (const T *base, unsigned int len, unsigned len_size) const 347 { 348 if (len_size >= 4) 349 { 350 if (unlikely (hb_unsigned_mul_overflows (len, hb_static_size (T), &len))) 351 return false; 352 } 353 else 354 len = len * hb_static_size (T); 355 return this->check_range (base, len); 356 } 357 358 template <typename T> check_arrayhb_sanitize_context_t359 bool check_array (const T *base, unsigned int len) const 360 { 361 return this->check_range (base, len, hb_static_size (T)); 362 } 363 364 template <typename T> check_arrayhb_sanitize_context_t365 bool check_array (const T *base, 366 unsigned int a, 367 unsigned int b) const 368 { 369 return this->check_range (base, hb_static_size (T), a, b); 370 } 371 check_start_recursionhb_sanitize_context_t372 bool check_start_recursion (int max_depth) 373 { 374 if (unlikely (recursion_depth >= max_depth)) return false; 375 return ++recursion_depth; 376 } 377 end_recursionhb_sanitize_context_t378 bool end_recursion (bool result) 379 { 380 recursion_depth--; 381 return result; 382 } 383 384 template <typename Type> 385 #ifndef HB_OPTIMIZE_SIZE 386 HB_ALWAYS_INLINE 387 #endif check_structhb_sanitize_context_t388 bool check_struct (const Type *obj) const 389 { 390 if (sizeof (uintptr_t) == sizeof (uint32_t)) 391 return likely (this->check_range_fast (obj, obj->min_size)); 392 else 393 return likely (this->check_point ((const char *) obj + obj->min_size)); 394 } 395 may_edithb_sanitize_context_t396 bool may_edit (const void *base, unsigned int len) 397 { 398 if (this->edit_count >= HB_SANITIZE_MAX_EDITS) 399 return false; 400 401 const char *p = (const char *) base; 402 this->edit_count++; 403 404 DEBUG_MSG_LEVEL (SANITIZE, p, this->debug_depth+1, 0, 405 "may_edit(%u) [%p..%p] (%u bytes) in [%p..%p] -> %s", 406 this->edit_count, 407 p, p + len, len, 408 this->start, this->end, 409 this->writable ? "GRANTED" : "DENIED"); 410 411 return this->writable; 412 } 413 414 template <typename Type, typename ValueType> try_sethb_sanitize_context_t415 bool try_set (const Type *obj, const ValueType &v) 416 { 417 if (this->may_edit (obj, hb_static_size (Type))) 418 { 419 * const_cast<Type *> (obj) = v; 420 return true; 421 } 422 return false; 423 } 424 425 template <typename Type> sanitize_blobhb_sanitize_context_t426 hb_blob_t *sanitize_blob (hb_blob_t *blob) 427 { 428 bool sane; 429 430 init (blob); 431 432 retry: 433 DEBUG_MSG_FUNC (SANITIZE, start, "start"); 434 435 start_processing (); 436 437 if (unlikely (!start)) 438 { 439 end_processing (); 440 return blob; 441 } 442 443 Type *t = reinterpret_cast<Type *> (const_cast<char *> (start)); 444 445 sane = t->sanitize (this); 446 if (sane) 447 { 448 if (edit_count) 449 { 450 DEBUG_MSG_FUNC (SANITIZE, start, "passed first round with %u edits; going for second round", edit_count); 451 452 /* sanitize again to ensure no toe-stepping */ 453 edit_count = 0; 454 sane = t->sanitize (this); 455 if (edit_count) { 456 DEBUG_MSG_FUNC (SANITIZE, start, "requested %u edits in second round; FAILING", edit_count); 457 sane = false; 458 } 459 } 460 } 461 else 462 { 463 if (edit_count && !writable) { 464 start = hb_blob_get_data_writable (blob, nullptr); 465 end = start + blob->length; 466 467 if (start) 468 { 469 writable = true; 470 /* ok, we made it writable by relocating. try again */ 471 DEBUG_MSG_FUNC (SANITIZE, start, "retry"); 472 goto retry; 473 } 474 } 475 } 476 477 end_processing (); 478 479 DEBUG_MSG_FUNC (SANITIZE, start, sane ? "PASSED" : "FAILED"); 480 if (sane) 481 { 482 hb_blob_make_immutable (blob); 483 return blob; 484 } 485 else 486 { 487 hb_blob_destroy (blob); 488 return hb_blob_get_empty (); 489 } 490 } 491 492 template <typename Type> reference_tablehb_sanitize_context_t493 hb_blob_t *reference_table (const hb_face_t *face, hb_tag_t tableTag = Type::tableTag) 494 { 495 if (!num_glyphs_set) 496 set_num_glyphs (hb_face_get_glyph_count (face)); 497 return sanitize_blob<Type> (hb_face_reference_table (face, tableTag)); 498 } 499 500 const char *start, *end; 501 unsigned length; 502 mutable int max_ops, max_subtables; 503 private: 504 int recursion_depth; 505 bool writable; 506 unsigned int edit_count; 507 hb_blob_t *blob; 508 unsigned int num_glyphs; 509 bool num_glyphs_set; 510 public: 511 bool lazy_some_gpos; 512 }; 513 514 struct hb_sanitize_with_object_t 515 { 516 template <typename T> hb_sanitize_with_object_thb_sanitize_with_object_t517 hb_sanitize_with_object_t (hb_sanitize_context_t *c, const T& obj) : c (c) 518 { c->set_object (obj); } ~hb_sanitize_with_object_thb_sanitize_with_object_t519 ~hb_sanitize_with_object_t () 520 { c->reset_object (); } 521 522 private: 523 hb_sanitize_context_t *c; 524 }; 525 526 527 #endif /* HB_SANITIZE_HH */ 528