sandbox/win/src/sharedmem_ipc_client.cc

   1 // Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include <string.h>
   6 #include "sandbox/win/src/sharedmem_ipc_client.h"
   7 #include "sandbox/win/src/sandbox.h"
   8 #include "sandbox/win/src/crosscall_client.h"
   9 #include "sandbox/win/src/crosscall_params.h"
  10 #include "base/logging.h"
  11
  12 namespace sandbox {
  13
  14 // Get the base of the data buffer of the channel; this is where the input
  15 // parameters get serialized. Since they get serialized directly into the
  16 // channel we avoid one copy.
  17 void* SharedMemIPCClient::GetBuffer() {
  18   bool failure = false;
  19   size_t ix = LockFreeChannel(&failure);
  20   if (failure) {
  21     return NULL;
  22   }
  23   return reinterpret_cast<char*>(control_) +
  24          control_->channels[ix].channel_base;
  25 }
  26
  27 // If we need to cancel an IPC before issuing DoCall
  28 // our client should call FreeBuffer with the same pointer
  29 // returned by GetBuffer.
  30 void SharedMemIPCClient::FreeBuffer(void* buffer) {
  31   size_t num = ChannelIndexFromBuffer(buffer);
  32   ChannelControl* channel = control_->channels;
  33   LONG result = ::InterlockedExchange(&channel[num].state, kFreeChannel);
  34   DCHECK_NE(kFreeChannel, static_cast<ChannelState>(result));
  35   result;
  36 }
  37
  38 // The constructor simply casts the shared memory to the internal
  39 // structures. This is a cheap step that is why this IPC object can
  40 // and should be constructed per call.
  41 SharedMemIPCClient::SharedMemIPCClient(void* shared_mem)
  42     : control_(reinterpret_cast<IPCControl*>(shared_mem)) {
  43   first_base_ = reinterpret_cast<char*>(shared_mem) +
  44                control_->channels[0].channel_base;
  45   // There must be at least one channel.
  46   DCHECK(0 != control_->channels_count);
  47 }
  48
  49 // Do the IPC. At this point the channel should have already been
  50 // filled with the serialized input parameters.
  51 // We follow the pattern explained in the header file.
  52 ResultCode SharedMemIPCClient::DoCall(CrossCallParams* params,
  53                                       CrossCallReturn* answer) {
  54   if (!control_->server_alive)
  55     return SBOX_ERROR_CHANNEL_ERROR;
  56
  57   size_t num = ChannelIndexFromBuffer(params->GetBuffer());
  58   ChannelControl* channel = control_->channels;
  59   // Note that the IPC tag goes outside the buffer as well inside
  60   // the buffer. This should enable the server to prioritize based on
  61   // IPC tags without having to de-serialize the entire message.
  62   channel[num].ipc_tag = params->GetTag();
  63
  64   // Wait for the server to service this IPC call. After kIPCWaitTimeOut1
  65   // we check if the server_alive mutex was abandoned which will indicate
  66   // that the server has died.
  67
  68   // While the atomic signaling and waiting is not a requirement, it
  69   // is nice because we save a trip to kernel.
  70   DWORD wait = ::SignalObjectAndWait(channel[num].ping_event,
  71                                      channel[num].pong_event,
  72                                      kIPCWaitTimeOut1, FALSE);
  73   if (WAIT_TIMEOUT == wait) {
  74     // The server is taking too long. Enter a loop were we check if the
  75     // server_alive mutex has been abandoned which would signal a server crash
  76     // or else we keep waiting for a response.
  77     while (true) {
  78       wait = ::WaitForSingleObject(control_->server_alive, 0);
  79       if (WAIT_TIMEOUT == wait) {
  80         // Server seems still alive. We already signaled so here we just wait.
  81         wait = ::WaitForSingleObject(channel[num].pong_event, kIPCWaitTimeOut1);
  82         if (WAIT_OBJECT_0 == wait) {
  83           // The server took a long time but responded.
  84           break;
  85         } else if (WAIT_TIMEOUT == wait) {
  86           continue;
  87         } else {
  88           return SBOX_ERROR_CHANNEL_ERROR;
  89         }
  90       } else {
  91         // The server has crashed and windows has signaled the mutex as
  92         // abandoned.
  93         ::InterlockedExchange(&channel[num].state, kAbandonnedChannel);
  94         control_->server_alive = 0;
  95         return SBOX_ERROR_CHANNEL_ERROR;
  96       }
  97     }
  98   } else if (WAIT_OBJECT_0 != wait) {
  99     // Probably the server crashed before the kIPCWaitTimeOut1 occurred.
 100     return SBOX_ERROR_CHANNEL_ERROR;
 101   }
 102
 103   // The server has returned an answer, copy it and free the channel.
 104   memcpy(answer, params->GetCallReturn(), sizeof(CrossCallReturn));
 105
 106   // Return the IPC state It can indicate that while the IPC has
 107   // completed some error in the Broker has caused to not return valid
 108   // results.
 109   return answer->call_outcome;
 110 }
 111
 112 // Locking a channel is a simple as looping over all the channels
 113 // looking for one that is has state = kFreeChannel and atomically
 114 // swapping it to kBusyChannel.
 115 // If there is no free channel, then we must back off so some other
 116 // thread makes progress and frees a channel. To back off we sleep.
 117 size_t SharedMemIPCClient::LockFreeChannel(bool* severe_failure) {
 118   if (0 == control_->channels_count) {
 119     *severe_failure = true;
 120     return 0;
 121   }
 122   ChannelControl* channel = control_->channels;
 123   do {
 124     for (size_t ix = 0; ix != control_->channels_count; ++ix) {
 125       if (kFreeChannel == ::InterlockedCompareExchange(&channel[ix].state,
 126                                                        kBusyChannel,
 127                                                        kFreeChannel)) {
 128           *severe_failure = false;
 129           return ix;
 130       }
 131     }
 132     // We did not find any available channel, maybe the server is dead.
 133     DWORD wait = ::WaitForSingleObject(control_->server_alive,
 134                                        kIPCWaitTimeOut2);
 135     if (WAIT_TIMEOUT != wait) {
 136       // The server is dead and we outlive it enough to get in trouble.
 137       *severe_failure = true;
 138       return 0;
 139     }
 140   }
 141   while (true);
 142 }
 143
 144 // Find out which channel we are from the pointer returned by GetBuffer.
 145 size_t SharedMemIPCClient::ChannelIndexFromBuffer(const void* buffer) {
 146   ptrdiff_t d = reinterpret_cast<const char*>(buffer) - first_base_;
 147   size_t num = d/kIPCChannelSize;
 148   DCHECK_LT(num, control_->channels_count);
 149   return (num);
 150 }
 151
 152 }  // namespace sandbox