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 max_ops (0), max_subtables (0), 126 recursion_depth (0), 127 writable (false), edit_count (0), 128 blob (nullptr), 129 num_glyphs (65536), 130 num_glyphs_set (false) {} 131 get_namehb_sanitize_context_t132 const char *get_name () { return "SANITIZE"; } 133 template <typename T, typename F> may_dispatchhb_sanitize_context_t134 bool may_dispatch (const T *obj HB_UNUSED, const F *format) 135 { return format->sanitize (this); } default_return_valuehb_sanitize_context_t136 static return_t default_return_value () { return true; } no_dispatch_return_valuehb_sanitize_context_t137 static return_t no_dispatch_return_value () { return false; } stop_sublookup_iterationhb_sanitize_context_t138 bool stop_sublookup_iteration (const return_t r) const { return !r; } 139 visit_subtableshb_sanitize_context_t140 bool visit_subtables (unsigned count) 141 { 142 max_subtables += count; 143 return max_subtables < HB_SANITIZE_MAX_SUBTABLES; 144 } 145 146 private: 147 template <typename T, typename ...Ts> auto 148 _dispatch (const T &obj, hb_priority<1>, Ts&&... ds) HB_AUTO_RETURN 149 ( obj.sanitize (this, std::forward<Ts> (ds)...) ) 150 template <typename T, typename ...Ts> auto 151 _dispatch (const T &obj, hb_priority<0>, Ts&&... ds) HB_AUTO_RETURN 152 ( obj.dispatch (this, std::forward<Ts> (ds)...) ) 153 public: 154 template <typename T, typename ...Ts> auto dispatchhb_sanitize_context_t155 dispatch (const T &obj, Ts&&... ds) HB_AUTO_RETURN 156 ( _dispatch (obj, hb_prioritize, std::forward<Ts> (ds)...) ) 157 158 159 void init (hb_blob_t *b) 160 { 161 this->blob = hb_blob_reference (b); 162 this->writable = false; 163 } 164 set_num_glyphshb_sanitize_context_t165 void set_num_glyphs (unsigned int num_glyphs_) 166 { 167 num_glyphs = num_glyphs_; 168 num_glyphs_set = true; 169 } get_num_glyphshb_sanitize_context_t170 unsigned int get_num_glyphs () { return num_glyphs; } 171 set_max_opshb_sanitize_context_t172 void set_max_ops (int max_ops_) { max_ops = max_ops_; } 173 174 template <typename T> set_objecthb_sanitize_context_t175 void set_object (const T *obj) 176 { 177 reset_object (); 178 179 if (!obj) return; 180 181 const char *obj_start = (const char *) obj; 182 if (unlikely (obj_start < this->start || this->end <= obj_start)) 183 this->start = this->end = nullptr; 184 else 185 { 186 this->start = obj_start; 187 this->end = obj_start + hb_min (size_t (this->end - obj_start), obj->get_size ()); 188 } 189 } 190 reset_objecthb_sanitize_context_t191 void reset_object () 192 { 193 this->start = this->blob->data; 194 this->end = this->start + this->blob->length; 195 assert (this->start <= this->end); /* Must not overflow. */ 196 } 197 start_processinghb_sanitize_context_t198 void start_processing () 199 { 200 reset_object (); 201 if (unlikely (hb_unsigned_mul_overflows (this->end - this->start, HB_SANITIZE_MAX_OPS_FACTOR))) 202 this->max_ops = HB_SANITIZE_MAX_OPS_MAX; 203 else 204 this->max_ops = hb_clamp ((unsigned) (this->end - this->start) * HB_SANITIZE_MAX_OPS_FACTOR, 205 (unsigned) HB_SANITIZE_MAX_OPS_MIN, 206 (unsigned) HB_SANITIZE_MAX_OPS_MAX); 207 this->edit_count = 0; 208 this->debug_depth = 0; 209 this->recursion_depth = 0; 210 211 DEBUG_MSG_LEVEL (SANITIZE, start, 0, +1, 212 "start [%p..%p] (%lu bytes)", 213 this->start, this->end, 214 (unsigned long) (this->end - this->start)); 215 } 216 end_processinghb_sanitize_context_t217 void end_processing () 218 { 219 DEBUG_MSG_LEVEL (SANITIZE, this->start, 0, -1, 220 "end [%p..%p] %u edit requests", 221 this->start, this->end, this->edit_count); 222 223 hb_blob_destroy (this->blob); 224 this->blob = nullptr; 225 this->start = this->end = nullptr; 226 } 227 get_edit_counthb_sanitize_context_t228 unsigned get_edit_count () { return edit_count; } 229 check_rangehb_sanitize_context_t230 bool check_range (const void *base, 231 unsigned int len) const 232 { 233 const char *p = (const char *) base; 234 bool ok = !len || 235 (this->start <= p && 236 p <= this->end && 237 (unsigned int) (this->end - p) >= len && 238 (this->max_ops -= len) > 0); 239 240 DEBUG_MSG_LEVEL (SANITIZE, p, this->debug_depth+1, 0, 241 "check_range [%p..%p]" 242 " (%d bytes) in [%p..%p] -> %s", 243 p, p + len, len, 244 this->start, this->end, 245 ok ? "OK" : "OUT-OF-RANGE"); 246 247 return likely (ok); 248 } 249 250 template <typename T> check_rangehb_sanitize_context_t251 bool check_range (const T *base, 252 unsigned int a, 253 unsigned int b) const 254 { 255 return !hb_unsigned_mul_overflows (a, b) && 256 this->check_range (base, a * b); 257 } 258 259 template <typename T> check_rangehb_sanitize_context_t260 bool check_range (const T *base, 261 unsigned int a, 262 unsigned int b, 263 unsigned int c) const 264 { 265 return !hb_unsigned_mul_overflows (a, b) && 266 this->check_range (base, a * b, c); 267 } 268 269 template <typename T> check_arrayhb_sanitize_context_t270 bool check_array (const T *base, unsigned int len) const 271 { 272 return this->check_range (base, len, hb_static_size (T)); 273 } 274 275 template <typename T> check_arrayhb_sanitize_context_t276 bool check_array (const T *base, 277 unsigned int a, 278 unsigned int b) const 279 { 280 return this->check_range (base, a, b, hb_static_size (T)); 281 } 282 check_start_recursionhb_sanitize_context_t283 bool check_start_recursion (int max_depth) 284 { 285 if (unlikely (recursion_depth >= max_depth)) return false; 286 return ++recursion_depth; 287 } 288 end_recursionhb_sanitize_context_t289 bool end_recursion (bool result) 290 { 291 recursion_depth--; 292 return result; 293 } 294 295 template <typename Type> check_structhb_sanitize_context_t296 bool check_struct (const Type *obj) const 297 { return likely (this->check_range (obj, obj->min_size)); } 298 may_edithb_sanitize_context_t299 bool may_edit (const void *base, unsigned int len) 300 { 301 if (this->edit_count >= HB_SANITIZE_MAX_EDITS) 302 return false; 303 304 const char *p = (const char *) base; 305 this->edit_count++; 306 307 DEBUG_MSG_LEVEL (SANITIZE, p, this->debug_depth+1, 0, 308 "may_edit(%u) [%p..%p] (%d bytes) in [%p..%p] -> %s", 309 this->edit_count, 310 p, p + len, len, 311 this->start, this->end, 312 this->writable ? "GRANTED" : "DENIED"); 313 314 return this->writable; 315 } 316 317 template <typename Type, typename ValueType> try_sethb_sanitize_context_t318 bool try_set (const Type *obj, const ValueType &v) 319 { 320 if (this->may_edit (obj, hb_static_size (Type))) 321 { 322 * const_cast<Type *> (obj) = v; 323 return true; 324 } 325 return false; 326 } 327 328 template <typename Type> sanitize_blobhb_sanitize_context_t329 hb_blob_t *sanitize_blob (hb_blob_t *blob) 330 { 331 bool sane; 332 333 init (blob); 334 335 retry: 336 DEBUG_MSG_FUNC (SANITIZE, start, "start"); 337 338 start_processing (); 339 340 if (unlikely (!start)) 341 { 342 end_processing (); 343 return blob; 344 } 345 346 Type *t = reinterpret_cast<Type *> (const_cast<char *> (start)); 347 348 sane = t->sanitize (this); 349 if (sane) 350 { 351 if (edit_count) 352 { 353 DEBUG_MSG_FUNC (SANITIZE, start, "passed first round with %d edits; going for second round", edit_count); 354 355 /* sanitize again to ensure no toe-stepping */ 356 edit_count = 0; 357 sane = t->sanitize (this); 358 if (edit_count) { 359 DEBUG_MSG_FUNC (SANITIZE, start, "requested %d edits in second round; FAILLING", edit_count); 360 sane = false; 361 } 362 } 363 } 364 else 365 { 366 if (edit_count && !writable) { 367 start = hb_blob_get_data_writable (blob, nullptr); 368 end = start + blob->length; 369 370 if (start) 371 { 372 writable = true; 373 /* ok, we made it writable by relocating. try again */ 374 DEBUG_MSG_FUNC (SANITIZE, start, "retry"); 375 goto retry; 376 } 377 } 378 } 379 380 end_processing (); 381 382 DEBUG_MSG_FUNC (SANITIZE, start, sane ? "PASSED" : "FAILED"); 383 if (sane) 384 { 385 hb_blob_make_immutable (blob); 386 return blob; 387 } 388 else 389 { 390 hb_blob_destroy (blob); 391 return hb_blob_get_empty (); 392 } 393 } 394 395 template <typename Type> reference_tablehb_sanitize_context_t396 hb_blob_t *reference_table (const hb_face_t *face, hb_tag_t tableTag = Type::tableTag) 397 { 398 if (!num_glyphs_set) 399 set_num_glyphs (hb_face_get_glyph_count (face)); 400 return sanitize_blob<Type> (hb_face_reference_table (face, tableTag)); 401 } 402 403 const char *start, *end; 404 mutable int max_ops, max_subtables; 405 private: 406 int recursion_depth; 407 bool writable; 408 unsigned int edit_count; 409 hb_blob_t *blob; 410 unsigned int num_glyphs; 411 bool num_glyphs_set; 412 }; 413 414 struct hb_sanitize_with_object_t 415 { 416 template <typename T> hb_sanitize_with_object_thb_sanitize_with_object_t417 hb_sanitize_with_object_t (hb_sanitize_context_t *c, const T& obj) : c (c) 418 { c->set_object (obj); } ~hb_sanitize_with_object_thb_sanitize_with_object_t419 ~hb_sanitize_with_object_t () 420 { c->reset_object (); } 421 422 private: 423 hb_sanitize_context_t *c; 424 }; 425 426 427 #endif /* HB_SANITIZE_HH */ 428