1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
|
/*
* Copyright © 2007,2008,2009,2010 Red Hat, Inc.
* Copyright © 2012,2018 Google, Inc.
*
* This is part of HarfBuzz, a text shaping library.
*
* Permission is hereby granted, without written agreement and without
* license or royalty fees, to use, copy, modify, and distribute this
* software and its documentation for any purpose, provided that the
* above copyright notice and the following two paragraphs appear in
* all copies of this software.
*
* IN NO EVENT SHALL THE COPYRIGHT HOLDER BE LIABLE TO ANY PARTY FOR
* DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES
* ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION, EVEN
* IF THE COPYRIGHT HOLDER HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH
* DAMAGE.
*
* THE COPYRIGHT HOLDER SPECIFICALLY DISCLAIMS ANY WARRANTIES, INCLUDING,
* BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
* FITNESS FOR A PARTICULAR PURPOSE. THE SOFTWARE PROVIDED HEREUNDER IS
* ON AN "AS IS" BASIS, AND THE COPYRIGHT HOLDER HAS NO OBLIGATION TO
* PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
*
* Red Hat Author(s): Behdad Esfahbod
* Google Author(s): Behdad Esfahbod
*/
#ifndef HB_SANITIZE_HH
#define HB_SANITIZE_HH
#include "hb.hh"
#include "hb-blob.hh"
#include "hb-dispatch.hh"
/*
* Sanitize
*
*
* === Introduction ===
*
* The sanitize machinery is at the core of our zero-cost font loading. We
* mmap() font file into memory and create a blob out of it. Font subtables
* are returned as a readonly sub-blob of the main font blob. These table
* blobs are then sanitized before use, to ensure invalid memory access does
* not happen. The toplevel sanitize API use is like, eg. to load the 'head'
* table:
*
* hb_blob_t *head_blob = hb_sanitize_context_t ().reference_table<OT::head> (face);
*
* The blob then can be converted to a head table struct with:
*
* const head *head_table = head_blob->as<head> ();
*
* What the reference_table does is, to call hb_face_reference_table() to load
* the table blob, sanitize it and return either the sanitized blob, or empty
* blob if sanitization failed. The blob->as() function returns the null
* object of its template type argument if the blob is empty. Otherwise, it
* just casts the blob contents to the desired type.
*
* Sanitizing a blob of data with a type T works as follows (with minor
* simplification):
*
* - Cast blob content to T*, call sanitize() method of it,
* - If sanitize succeeded, return blob.
* - Otherwise, if blob is not writable, try making it writable,
* or copy if cannot be made writable in-place,
* - Call sanitize() again. Return blob if sanitize succeeded.
* - Return empty blob otherwise.
*
*
* === The sanitize() contract ===
*
* The sanitize() method of each object type shall return true if it's safe to
* call other methods of the object, and %false otherwise.
*
* Note that what sanitize() checks for might align with what the specification
* describes as valid table data, but does not have to be. In particular, we
* do NOT want to be pedantic and concern ourselves with validity checks that
* are irrelevant to our use of the table. On the contrary, we want to be
* lenient with error handling and accept invalid data to the extent that it
* does not impose extra burden on us.
*
* Based on the sanitize contract, one can see that what we check for depends
* on how we use the data in other table methods. Ie. if other table methods
* assume that offsets do NOT point out of the table data block, then that's
* something sanitize() must check for (GSUB/GPOS/GDEF/etc work this way). On
* the other hand, if other methods do such checks themselves, then sanitize()
* does not have to bother with them (glyf/local work this way). The choice
* depends on the table structure and sanitize() performance. For example, to
* check glyf/loca offsets in sanitize() would cost O(num-glyphs). We try hard
* to avoid such costs during font loading. By postponing such checks to the
* actual glyph loading, we reduce the sanitize cost to O(1) and total runtime
* cost to O(used-glyphs). As such, this is preferred.
*
* The same argument can be made re GSUB/GPOS/GDEF, but there, the table
* structure is so complicated that by checking all offsets at sanitize() time,
* we make the code much simpler in other methods, as offsets and referenced
* objects do not need to be validated at each use site.
*/
/* This limits sanitizing time on really broken fonts. */
#ifndef HB_SANITIZE_MAX_EDITS
#define HB_SANITIZE_MAX_EDITS 32
#endif
#ifndef HB_SANITIZE_MAX_OPS_FACTOR
#define HB_SANITIZE_MAX_OPS_FACTOR 64
#endif
#ifndef HB_SANITIZE_MAX_OPS_MIN
#define HB_SANITIZE_MAX_OPS_MIN 16384
#endif
#ifndef HB_SANITIZE_MAX_OPS_MAX
#define HB_SANITIZE_MAX_OPS_MAX 0x3FFFFFFF
#endif
#ifndef HB_SANITIZE_MAX_SUBTABLES
#define HB_SANITIZE_MAX_SUBTABLES 0x4000
#endif
struct hb_sanitize_context_t :
hb_dispatch_context_t<hb_sanitize_context_t, bool, HB_DEBUG_SANITIZE>
{
hb_sanitize_context_t () :
start (nullptr), end (nullptr),
max_ops (0), max_subtables (0),
recursion_depth (0),
writable (false), edit_count (0),
blob (nullptr),
num_glyphs (65536),
num_glyphs_set (false) {}
const char *get_name () { return "SANITIZE"; }
template <typename T, typename F>
bool may_dispatch (const T *obj HB_UNUSED, const F *format)
{ return format->sanitize (this); }
static return_t default_return_value () { return true; }
static return_t no_dispatch_return_value () { return false; }
bool stop_sublookup_iteration (const return_t r) const { return !r; }
bool visit_subtables (unsigned count)
{
max_subtables += count;
return max_subtables < HB_SANITIZE_MAX_SUBTABLES;
}
private:
template <typename T, typename ...Ts> auto
_dispatch (const T &obj, hb_priority<1>, Ts&&... ds) HB_AUTO_RETURN
( obj.sanitize (this, std::forward<Ts> (ds)...) )
template <typename T, typename ...Ts> auto
_dispatch (const T &obj, hb_priority<0>, Ts&&... ds) HB_AUTO_RETURN
( obj.dispatch (this, std::forward<Ts> (ds)...) )
public:
template <typename T, typename ...Ts> auto
dispatch (const T &obj, Ts&&... ds) HB_AUTO_RETURN
( _dispatch (obj, hb_prioritize, std::forward<Ts> (ds)...) )
void init (hb_blob_t *b)
{
this->blob = hb_blob_reference (b);
this->writable = false;
}
void set_num_glyphs (unsigned int num_glyphs_)
{
num_glyphs = num_glyphs_;
num_glyphs_set = true;
}
unsigned int get_num_glyphs () { return num_glyphs; }
void set_max_ops (int max_ops_) { max_ops = max_ops_; }
template <typename T>
void set_object (const T *obj)
{
reset_object ();
if (!obj) return;
const char *obj_start = (const char *) obj;
if (unlikely (obj_start < this->start || this->end <= obj_start))
this->start = this->end = nullptr;
else
{
this->start = obj_start;
this->end = obj_start + hb_min (size_t (this->end - obj_start), obj->get_size ());
}
}
void reset_object ()
{
this->start = this->blob->data;
this->end = this->start + this->blob->length;
assert (this->start <= this->end); /* Must not overflow. */
}
void start_processing ()
{
reset_object ();
unsigned m;
if (unlikely (hb_unsigned_mul_overflows (this->end - this->start, HB_SANITIZE_MAX_OPS_FACTOR, &m)))
this->max_ops = HB_SANITIZE_MAX_OPS_MAX;
else
this->max_ops = hb_clamp (m,
(unsigned) HB_SANITIZE_MAX_OPS_MIN,
(unsigned) HB_SANITIZE_MAX_OPS_MAX);
this->edit_count = 0;
this->debug_depth = 0;
this->recursion_depth = 0;
DEBUG_MSG_LEVEL (SANITIZE, start, 0, +1,
"start [%p..%p] (%lu bytes)",
this->start, this->end,
(unsigned long) (this->end - this->start));
}
void end_processing ()
{
DEBUG_MSG_LEVEL (SANITIZE, this->start, 0, -1,
"end [%p..%p] %u edit requests",
this->start, this->end, this->edit_count);
hb_blob_destroy (this->blob);
this->blob = nullptr;
this->start = this->end = nullptr;
}
unsigned get_edit_count () { return edit_count; }
bool check_range (const void *base,
unsigned int len) const
{
const char *p = (const char *) base;
bool ok = !len ||
(this->start <= p &&
p <= this->end &&
(unsigned int) (this->end - p) >= len &&
(this->max_ops -= len) > 0);
DEBUG_MSG_LEVEL (SANITIZE, p, this->debug_depth+1, 0,
"check_range [%p..%p]"
" (%d bytes) in [%p..%p] -> %s",
p, p + len, len,
this->start, this->end,
ok ? "OK" : "OUT-OF-RANGE");
return likely (ok);
}
template <typename T>
bool check_range (const T *base,
unsigned int a,
unsigned int b) const
{
unsigned m;
return !hb_unsigned_mul_overflows (a, b, &m) &&
this->check_range (base, m);
}
template <typename T>
bool check_range (const T *base,
unsigned int a,
unsigned int b,
unsigned int c) const
{
unsigned m;
return !hb_unsigned_mul_overflows (a, b, &m) &&
this->check_range (base, m, c);
}
template <typename T>
bool check_array (const T *base, unsigned int len) const
{
return this->check_range (base, len, hb_static_size (T));
}
template <typename T>
bool check_array (const T *base,
unsigned int a,
unsigned int b) const
{
return this->check_range (base, a, b, hb_static_size (T));
}
bool check_start_recursion (int max_depth)
{
if (unlikely (recursion_depth >= max_depth)) return false;
return ++recursion_depth;
}
bool end_recursion (bool result)
{
recursion_depth--;
return result;
}
template <typename Type>
bool check_struct (const Type *obj) const
{ return likely (this->check_range (obj, obj->min_size)); }
bool may_edit (const void *base, unsigned int len)
{
if (this->edit_count >= HB_SANITIZE_MAX_EDITS)
return false;
const char *p = (const char *) base;
this->edit_count++;
DEBUG_MSG_LEVEL (SANITIZE, p, this->debug_depth+1, 0,
"may_edit(%u) [%p..%p] (%d bytes) in [%p..%p] -> %s",
this->edit_count,
p, p + len, len,
this->start, this->end,
this->writable ? "GRANTED" : "DENIED");
return this->writable;
}
template <typename Type, typename ValueType>
bool try_set (const Type *obj, const ValueType &v)
{
if (this->may_edit (obj, hb_static_size (Type)))
{
* const_cast<Type *> (obj) = v;
return true;
}
return false;
}
template <typename Type>
hb_blob_t *sanitize_blob (hb_blob_t *blob)
{
bool sane;
init (blob);
retry:
DEBUG_MSG_FUNC (SANITIZE, start, "start");
start_processing ();
if (unlikely (!start))
{
end_processing ();
return blob;
}
Type *t = reinterpret_cast<Type *> (const_cast<char *> (start));
sane = t->sanitize (this);
if (sane)
{
if (edit_count)
{
DEBUG_MSG_FUNC (SANITIZE, start, "passed first round with %d edits; going for second round", edit_count);
/* sanitize again to ensure no toe-stepping */
edit_count = 0;
sane = t->sanitize (this);
if (edit_count) {
DEBUG_MSG_FUNC (SANITIZE, start, "requested %d edits in second round; FAILLING", edit_count);
sane = false;
}
}
}
else
{
if (edit_count && !writable) {
start = hb_blob_get_data_writable (blob, nullptr);
end = start + blob->length;
if (start)
{
writable = true;
/* ok, we made it writable by relocating. try again */
DEBUG_MSG_FUNC (SANITIZE, start, "retry");
goto retry;
}
}
}
end_processing ();
DEBUG_MSG_FUNC (SANITIZE, start, sane ? "PASSED" : "FAILED");
if (sane)
{
hb_blob_make_immutable (blob);
return blob;
}
else
{
hb_blob_destroy (blob);
return hb_blob_get_empty ();
}
}
template <typename Type>
hb_blob_t *reference_table (const hb_face_t *face, hb_tag_t tableTag = Type::tableTag)
{
if (!num_glyphs_set)
set_num_glyphs (hb_face_get_glyph_count (face));
return sanitize_blob<Type> (hb_face_reference_table (face, tableTag));
}
const char *start, *end;
mutable int max_ops, max_subtables;
private:
int recursion_depth;
bool writable;
unsigned int edit_count;
hb_blob_t *blob;
unsigned int num_glyphs;
bool num_glyphs_set;
};
struct hb_sanitize_with_object_t
{
template <typename T>
hb_sanitize_with_object_t (hb_sanitize_context_t *c, const T& obj) : c (c)
{ c->set_object (obj); }
~hb_sanitize_with_object_t ()
{ c->reset_object (); }
private:
hb_sanitize_context_t *c;
};
#endif /* HB_SANITIZE_HH */
|