1 files changed, 458 insertions, 0 deletions
diff --git a/ipc/glue/Shmem.cpp b/ipc/glue/Shmem.cpp
new file mode 100644
index 0000000000..775d852faa
--- /dev/null
+++ b/ipc/glue/Shmem.cpp
@@ -0,0 +1,458 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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 "ShmemMessageUtils.h"
+#include "chrome/common/ipc_message_utils.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)
+      : IPC::Message(
+            routingId, SHMEM_CREATED_MESSAGE_TYPE, 0,
+            HeaderFlags(NESTED_INSIDE_CPOW, CONTROL_PRIORITY, COMPRESSION_NONE,
+                        LAZY_SEND, NOT_CONSTRUCTOR, ASYNC, NOT_REPLY)) {
+    MOZ_RELEASE_ASSERT(aSize < std::numeric_limits<uint32_t>::max(),
+                       "Tried to create Shmem with size larger than 4GB");
+    IPC::MessageWriter writer(*this);
+    IPC::WriteParam(&writer, aIPDLId);
+    IPC::WriteParam(&writer, uint32_t(aSize));
+  }
+
+  static bool ReadInfo(IPC::MessageReader* aReader, id_t* aIPDLId,
+                       size_t* aSize) {
+    uint32_t size = 0;
+    if (!IPC::ReadParam(aReader, aIPDLId) || !IPC::ReadParam(aReader, &size)) {
+      return false;
+    }
+    *aSize = size;
+    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, 0,
+            HeaderFlags(NOT_NESTED, NORMAL_PRIORITY, COMPRESSION_NONE,
+                        LAZY_SEND, NOT_CONSTRUCTOR, ASYNC, NOT_REPLY)) {
+    IPC::MessageWriter writer(*this);
+    IPC::WriteParam(&writer, aIPDLId);
+  }
+};
+
+static SharedMemory* NewSegment() { return new SharedMemoryBasic; }
+
+static already_AddRefed<SharedMemory> CreateSegment(size_t aNBytes,
+                                                    size_t aExtraSize) {
+  RefPtr<SharedMemory> segment = NewSegment();
+  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;
+  }
+  IPC::MessageReader reader(aDescriptor);
+  if (!ShmemCreated::ReadInfo(&reader, aId, aNBytes)) {
+    return nullptr;
+  }
+  RefPtr<SharedMemory> segment = NewSegment();
+  if (!segment) {
+    return nullptr;
+  }
+  if (!segment->ReadHandle(&reader)) {
+    NS_ERROR("trying to open invalid handle");
+    return nullptr;
+  }
+  reader.EndRead();
+  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(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();
+  MOZ_ASSERT(mSegment->Size() - (2 * pageSize) >= mSize,
+             "illegal size in shared memory segment");
+
+  // 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() {
+  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(size_t aNBytes, 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(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(
+    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(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)
+
+Shmem::Shmem(SharedMemory* aSegment, id_t aId)
+    : mSegment(aSegment), mData(aSegment->memory()), mSize(0), mId(aId) {
+  mSize = static_cast<size_t>(*PtrToSize(mSegment));
+  MOZ_RELEASE_ASSERT(mSegment->Size() - sizeof(uint32_t) >= mSize,
+                     "illegal size in shared memory segment");
+}
+
+// static
+already_AddRefed<Shmem::SharedMemory> Shmem::Alloc(size_t aNBytes,
+                                                   bool /*unused*/,
+                                                   bool /*unused*/) {
+  RefPtr<SharedMemory> segment = CreateSegment(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(
+    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(SharedMemory* aSegment) { DestroySegment(aSegment); }
+
+#endif  // if defined(DEBUG)
+
+UniquePtr<IPC::Message> Shmem::MkCreatedMessage(int32_t routingId) {
+  AssertInvariants();
+
+  auto msg = MakeUnique<ShmemCreated>(routingId, mId, mSize);
+  IPC::MessageWriter writer(*msg);
+  if (!mSegment->WriteHandle(&writer)) {
+    return nullptr;
+  }
+  // close the handle to the segment after it is shared
+  mSegment->CloseHandle();
+  return msg;
+}
+
+UniquePtr<IPC::Message> Shmem::MkDestroyedMessage(int32_t routingId) {
+  AssertInvariants();
+  return MakeUnique<ShmemDestroyed>(routingId, mId);
+}
+
+void IPDLParamTraits<Shmem>::Write(IPC::MessageWriter* aWriter,
+                                   IProtocol* aActor, Shmem&& aParam) {
+  WriteIPDLParam(aWriter, aActor, aParam.mId);
+
+  aParam.RevokeRights();
+  aParam.forget();
+}
+
+bool IPDLParamTraits<Shmem>::Read(IPC::MessageReader* aReader,
+                                  IProtocol* aActor, paramType* aResult) {
+  paramType::id_t id;
+  if (!ReadIPDLParam(aReader, aActor, &id)) {
+    return false;
+  }
+
+  Shmem::SharedMemory* rawmem = aActor->LookupSharedMemory(id);
+  if (rawmem) {
+    *aResult = Shmem(rawmem, id);
+    return true;
+  }
+  *aResult = Shmem();
+  return true;
+}
+
+}  // namespace ipc
+}  // namespace mozilla