summaryrefslogtreecommitdiff
path: root/ipc/glue/Shmem.cpp
blob: 34d771ee386f92324dd9b3a6c590f595aba31c5b (plain)
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
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#include "Shmem.h"

#include "ProtocolUtils.h"
#include "SharedMemoryBasic.h"

#include "mozilla/Unused.h"


namespace mozilla {
namespace ipc {

class ShmemCreated : public IPC::Message
{
private:
  typedef Shmem::id_t id_t;

public:
  ShmemCreated(int32_t routingId,
               id_t aIPDLId,
               size_t aSize,
               SharedMemory::SharedMemoryType aType) :
    IPC::Message(routingId, SHMEM_CREATED_MESSAGE_TYPE, NESTED_INSIDE_CPOW)
  {
    IPC::WriteParam(this, aIPDLId);
    IPC::WriteParam(this, aSize);
    IPC::WriteParam(this, int32_t(aType));
  }

  static bool
  ReadInfo(const Message* msg, PickleIterator* iter,
           id_t* aIPDLId,
           size_t* aSize,
           SharedMemory::SharedMemoryType* aType)
  {
    if (!IPC::ReadParam(msg, iter, aIPDLId) ||
        !IPC::ReadParam(msg, iter, aSize) ||
        !IPC::ReadParam(msg, iter, reinterpret_cast<int32_t*>(aType)))
      return false;
    return true;
  }

  void Log(const std::string& aPrefix,
           FILE* aOutf) const
  {
    fputs("(special ShmemCreated msg)", aOutf);
  }
};

class ShmemDestroyed : public IPC::Message
{
private:
  typedef Shmem::id_t id_t;

public:
  ShmemDestroyed(int32_t routingId,
                 id_t aIPDLId) :
    IPC::Message(routingId, SHMEM_DESTROYED_MESSAGE_TYPE)
  {
    IPC::WriteParam(this, aIPDLId);
  }
};

static SharedMemory*
NewSegment(SharedMemory::SharedMemoryType aType)
{
  if (SharedMemory::TYPE_BASIC == aType) {
    return new SharedMemoryBasic;
  } else {
    NS_ERROR("unknown Shmem type");
    return nullptr;
  }
}

static already_AddRefed<SharedMemory>
CreateSegment(SharedMemory::SharedMemoryType aType, size_t aNBytes, size_t aExtraSize)
{
  RefPtr<SharedMemory> segment = NewSegment(aType);
  if (!segment) {
    return nullptr;
  }
  size_t size = SharedMemory::PageAlignedSize(aNBytes + aExtraSize);
  if (!segment->Create(size) || !segment->Map(size)) {
    return nullptr;
  }
  return segment.forget();
}

static already_AddRefed<SharedMemory>
ReadSegment(const IPC::Message& aDescriptor, Shmem::id_t* aId, size_t* aNBytes, size_t aExtraSize)
{
  if (SHMEM_CREATED_MESSAGE_TYPE != aDescriptor.type()) {
    NS_ERROR("expected 'shmem created' message");
    return nullptr;
  }
  SharedMemory::SharedMemoryType type;
  PickleIterator iter(aDescriptor);
  if (!ShmemCreated::ReadInfo(&aDescriptor, &iter, aId, aNBytes, &type)) {
    return nullptr;
  }
  RefPtr<SharedMemory> segment = NewSegment(type);
  if (!segment) {
    return nullptr;
  }
  if (!segment->ReadHandle(&aDescriptor, &iter)) {
    NS_ERROR("trying to open invalid handle");
    return nullptr;
  }
  aDescriptor.EndRead(iter);
  size_t size = SharedMemory::PageAlignedSize(*aNBytes + aExtraSize);
  if (!segment->Map(size)) {
    return nullptr;
  }
  // close the handle to the segment after it is mapped
  segment->CloseHandle();
  return segment.forget();
}

static void
DestroySegment(SharedMemory* aSegment)
{
  // the SharedMemory dtor closes and unmaps the actual OS shmem segment
  if (aSegment) {
    aSegment->Release();
  }
}


#if defined(DEBUG)

static const char sMagic[] =
    "This little piggy went to market.\n"
    "This little piggy stayed at home.\n"
    "This little piggy has roast beef,\n"
    "This little piggy had none.\n"
    "And this little piggy cried \"Wee! Wee! Wee!\" all the way home";


struct Header {
  // Don't use size_t or bool here because their size depends on the
  // architecture.
  uint32_t mSize;
  uint32_t mUnsafe;
  char mMagic[sizeof(sMagic)];
};

static void
GetSections(Shmem::SharedMemory* aSegment,
            Header** aHeader,
            char** aFrontSentinel,
            char** aData,
            char** aBackSentinel)
{
  MOZ_ASSERT(aSegment && aFrontSentinel && aData && aBackSentinel,
             "null param(s)");

  *aFrontSentinel = reinterpret_cast<char*>(aSegment->memory());
  MOZ_ASSERT(*aFrontSentinel, "null memory()");

  *aHeader = reinterpret_cast<Header*>(*aFrontSentinel);

  size_t pageSize = Shmem::SharedMemory::SystemPageSize();
  *aData = *aFrontSentinel + pageSize;

  *aBackSentinel = *aFrontSentinel + aSegment->Size() - pageSize;
}

static Header*
GetHeader(Shmem::SharedMemory* aSegment)
{
  Header* header;
  char* dontcare;
  GetSections(aSegment, &header, &dontcare, &dontcare, &dontcare);
  return header;
}

static void
Protect(SharedMemory* aSegment)
{
  MOZ_ASSERT(aSegment, "null segment");
  aSegment->Protect(reinterpret_cast<char*>(aSegment->memory()),
                    aSegment->Size(),
                    RightsNone);
}

static void
Unprotect(SharedMemory* aSegment)
{
  MOZ_ASSERT(aSegment, "null segment");
  aSegment->Protect(reinterpret_cast<char*>(aSegment->memory()),
                    aSegment->Size(),
                    RightsRead | RightsWrite);
}

//
// In debug builds, we specially allocate shmem segments.  The layout
// is as follows
//
//   Page 0: "front sentinel"
//     size of mapping
//     magic bytes
//   Page 1 through n-1:
//     user data
//   Page n: "back sentinel"
//     [nothing]
//
// The mapping can be in one of the following states, wrt to the
// current process.
//
//   State "unmapped": all pages are mapped with no access rights.
//
//   State "mapping": all pages are mapped with read/write access.
//
//   State "mapped": the front and back sentinels are mapped with no
//     access rights, and all the other pages are mapped with
//     read/write access.
//
// When a SharedMemory segment is first allocated, it starts out in
// the "mapping" state for the process that allocates the segment, and
// in the "unmapped" state for the other process.  The allocating
// process will then create a Shmem, which takes the segment into the
// "mapped" state, where it can be accessed by clients.
//
// When a Shmem is sent to another process in an IPDL message, the
// segment transitions into the "unmapped" state for the sending
// process, and into the "mapping" state for the receiving process.
// The receiving process will then create a Shmem from the underlying
// segment, and take the segment into the "mapped" state.
//
// In the "mapping" state, we use the front sentinel to verify the
// integrity of the shmem segment.  If valid, it has a size_t
// containing the number of bytes the user allocated followed by the
// magic bytes above.
//
// In the "mapped" state, the front and back sentinels have no access
// rights.  They act as guards against buffer overflows and underflows
// in client code; if clients touch a sentinel, they die with SIGSEGV.
//
// The "unmapped" state is used to enforce single-owner semantics of
// the shmem segment.  If a process other than the current owner tries
// to touch the segment, it dies with SIGSEGV.
//

Shmem::Shmem(IHadBetterBeIPDLCodeCallingThis_OtherwiseIAmADoodyhead,
             SharedMemory* aSegment, id_t aId) :
    mSegment(aSegment),
    mData(nullptr),
    mSize(0)
{
  MOZ_ASSERT(mSegment, "null segment");
  MOZ_ASSERT(aId != 0, "invalid ID");

  Unprotect(mSegment);

  Header* header;
  char* frontSentinel;
  char* data;
  char* backSentinel;
  GetSections(aSegment, &header, &frontSentinel, &data, &backSentinel);

  // do a quick validity check to avoid weird-looking crashes in libc
  char check = *frontSentinel;
  (void)check;

  MOZ_ASSERT(!strncmp(header->mMagic, sMagic, sizeof(sMagic)),
             "invalid segment");
  mSize = static_cast<size_t>(header->mSize);

  size_t pageSize = SharedMemory::SystemPageSize();
  // transition into the "mapped" state by protecting the front and
  // back sentinels (which guard against buffer under/overflows)
  mSegment->Protect(frontSentinel, pageSize, RightsNone);
  mSegment->Protect(backSentinel, pageSize, RightsNone);

  // don't set these until we know they're valid
  mData = data;
  mId = aId;
}

void
Shmem::AssertInvariants() const
{
  MOZ_ASSERT(mSegment, "null segment");
  MOZ_ASSERT(mData, "null data pointer");
  MOZ_ASSERT(mSize > 0, "invalid size");
  // if the segment isn't owned by the current process, these will
  // trigger SIGSEGV
  char checkMappingFront = *reinterpret_cast<char*>(mData);
  char checkMappingBack = *(reinterpret_cast<char*>(mData) + mSize - 1);

  // avoid "unused" warnings for these variables:
  Unused << checkMappingFront;
  Unused << checkMappingBack;
}

void
Shmem::RevokeRights(IHadBetterBeIPDLCodeCallingThis_OtherwiseIAmADoodyhead)
{
  AssertInvariants();

  size_t pageSize = SharedMemory::SystemPageSize();
  Header* header = GetHeader(mSegment);

  // Open this up for reading temporarily
  mSegment->Protect(reinterpret_cast<char*>(header), pageSize, RightsRead);

  if (!header->mUnsafe) {
    Protect(mSegment);
  } else {
    mSegment->Protect(reinterpret_cast<char*>(header), pageSize, RightsNone);
  }
}

// static
already_AddRefed<Shmem::SharedMemory>
Shmem::Alloc(IHadBetterBeIPDLCodeCallingThis_OtherwiseIAmADoodyhead,
             size_t aNBytes,
             SharedMemoryType aType,
             bool aUnsafe,
             bool aProtect)
{
  NS_ASSERTION(aNBytes <= UINT32_MAX, "Will truncate shmem segment size!");
  MOZ_ASSERT(!aProtect || !aUnsafe, "protect => !unsafe");

  size_t pageSize = SharedMemory::SystemPageSize();
  // |2*pageSize| is for the front and back sentinel
  RefPtr<SharedMemory> segment = CreateSegment(aType, aNBytes, 2*pageSize);
  if (!segment) {
    return nullptr;
  }

  Header* header;
  char *frontSentinel;
  char *data;
  char *backSentinel;
  GetSections(segment, &header, &frontSentinel, &data, &backSentinel);

  // initialize the segment with Shmem-internal information

  // NB: this can't be a static assert because technically pageSize
  // isn't known at compile time, event though in practice it's always
  // going to be 4KiB
  MOZ_ASSERT(sizeof(Header) <= pageSize,
             "Shmem::Header has gotten too big");
  memcpy(header->mMagic, sMagic, sizeof(sMagic));
  header->mSize = static_cast<uint32_t>(aNBytes);
  header->mUnsafe = aUnsafe;

  if (aProtect)
    Protect(segment);

  return segment.forget();
}

// static
already_AddRefed<Shmem::SharedMemory>
Shmem::OpenExisting(IHadBetterBeIPDLCodeCallingThis_OtherwiseIAmADoodyhead,
                    const IPC::Message& aDescriptor,
                    id_t* aId,
                    bool aProtect)
{
  size_t size;
  size_t pageSize = SharedMemory::SystemPageSize();
  // |2*pageSize| is for the front and back sentinels
  RefPtr<SharedMemory> segment = ReadSegment(aDescriptor, aId, &size, 2*pageSize);
  if (!segment) {
    return nullptr;
  }

  Header* header = GetHeader(segment);

  if (size != header->mSize) {
    // Deallocation should zero out the header, so check for that.
    if (header->mSize || header->mUnsafe || header->mMagic[0] ||
        memcmp(header->mMagic, &header->mMagic[1], sizeof(header->mMagic)-1)) {
      NS_ERROR("Wrong size for this Shmem!");
    } else {
      NS_WARNING("Shmem was deallocated");
    }
    return nullptr;
  }

  // The caller of this function may not know whether the segment is
  // unsafe or not
  if (!header->mUnsafe && aProtect)
    Protect(segment);

  return segment.forget();
}

// static
void
Shmem::Dealloc(IHadBetterBeIPDLCodeCallingThis_OtherwiseIAmADoodyhead,
               SharedMemory* aSegment)
{
  if (!aSegment)
    return;

  size_t pageSize = SharedMemory::SystemPageSize();
  Header* header;
  char *frontSentinel;
  char *data;
  char *backSentinel;
  GetSections(aSegment, &header, &frontSentinel, &data, &backSentinel);

  aSegment->Protect(frontSentinel, pageSize, RightsWrite | RightsRead);
  memset(header->mMagic, 0, sizeof(sMagic));
  header->mSize = 0;
  header->mUnsafe = false;          // make it "safe" so as to catch errors

  DestroySegment(aSegment);
}


#else  // !defined(DEBUG)

// static
already_AddRefed<Shmem::SharedMemory>
Shmem::Alloc(IHadBetterBeIPDLCodeCallingThis_OtherwiseIAmADoodyhead,
             size_t aNBytes,
             SharedMemoryType aType,
             bool /*unused*/,
             bool /*unused*/)
{
  RefPtr<SharedMemory> segment = CreateSegment(aType, aNBytes, sizeof(uint32_t));
  if (!segment) {
    return nullptr;
  }

  *PtrToSize(segment) = static_cast<uint32_t>(aNBytes);

  return segment.forget();
}

// static
already_AddRefed<Shmem::SharedMemory>
Shmem::OpenExisting(IHadBetterBeIPDLCodeCallingThis_OtherwiseIAmADoodyhead,
                    const IPC::Message& aDescriptor,
                    id_t* aId,
                    bool /*unused*/)
{
  size_t size;
  RefPtr<SharedMemory> segment = ReadSegment(aDescriptor, aId, &size, sizeof(uint32_t));
  if (!segment) {
    return nullptr;
  }

  // this is the only validity check done in non-DEBUG builds
  if (size != static_cast<size_t>(*PtrToSize(segment))) {
    return nullptr;
  }

  return segment.forget();
}

// static
void
Shmem::Dealloc(IHadBetterBeIPDLCodeCallingThis_OtherwiseIAmADoodyhead,
               SharedMemory* aSegment)
{
  DestroySegment(aSegment);
}

#endif  // if defined(DEBUG)

IPC::Message*
Shmem::ShareTo(IHadBetterBeIPDLCodeCallingThis_OtherwiseIAmADoodyhead,
               base::ProcessId aTargetPid,
               int32_t routingId)
{
  AssertInvariants();

  IPC::Message *msg = new ShmemCreated(routingId, mId, mSize, mSegment->Type());
  if (!mSegment->ShareHandle(aTargetPid, msg)) {
    return nullptr;
  }
  // close the handle to the segment after it is shared
  mSegment->CloseHandle();
  return msg;
}

IPC::Message*
Shmem::UnshareFrom(IHadBetterBeIPDLCodeCallingThis_OtherwiseIAmADoodyhead,
                   base::ProcessId aTargetPid,
                   int32_t routingId)
{
  AssertInvariants();
  return new ShmemDestroyed(routingId, mId);
}

} // namespace ipc
} // namespace mozilla