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+// Copyright 2008, Google Inc.
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//    * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//    * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//    * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#ifndef SANDBOX_SRC_POLICY_ENGINE_PARAMS_H__
+#define SANDBOX_SRC_POLICY_ENGINE_PARAMS_H__
+
+#include "base/basictypes.h"
+#include "sandbox/src/internal_types.h"
+#include "sandbox/src/nt_internals.h"
+#include "sandbox/src/sandbox_nt_util.h"
+
+// This header defines the classes that allow the low level policy to select
+// the input parameters. In order to better make sense of this header is
+// recommended that you check policy_engine_opcodes.h first.
+
+namespace sandbox {
+
+// Models the set of interesting parameters of an intercepted system call
+// normally you don't create objects of this class directly, instead you
+// use the POLPARAMS_XXX macros.
+// For example, if an intercepted function has the following signature:
+//
+// NTSTATUS NtOpenFileFunction (PHANDLE FileHandle,
+//                              ACCESS_MASK DesiredAccess,
+//                              POBJECT_ATTRIBUTES ObjectAttributes,
+//                              PIO_STATUS_BLOCK IoStatusBlock,
+//                              ULONG ShareAccess,
+//                              ULONG OpenOptions);
+//
+// You could say that the following parameters are of interest to policy:
+//
+//   POLPARAMS_BEGIN(open_params)
+//      POLPARAM(DESIRED_ACCESS)
+//      POLPARAM(OBJECT_NAME)
+//      POLPARAM(SECURITY_DESCRIPTOR)
+//      POLPARAM(IO_STATUS)
+//      POLPARAM(OPEN_OPTIONS)
+//   POLPARAMS_END;
+//
+// and the actual code will use this for defining the parameters:
+//
+//   CountedParameterSet<open_params> p;
+//   p[open_params::DESIRED_ACCESS] = ParamPickerMake(DesiredAccess);
+//   p[open_params::OBJECT_NAME] =
+//       ParamPickerMake(ObjectAttributes->ObjectName);
+//   p[open_params::SECURITY_DESCRIPTOR] =
+//       ParamPickerMake(ObjectAttributes->SecurityDescriptor);
+//   p[open_params::IO_STATUS] = ParamPickerMake(IoStatusBlock);
+//   p[open_params::OPEN_OPTIONS] = ParamPickerMake(OpenOptions);
+//
+//  These will create an stack-allocated array of ParameterSet objects which
+//  have each 1) the address of the parameter 2) a numeric id that encodes the
+//  original C++ type. This allows the policy to treat any set of supported
+//  argument types uniformily and with some type safety.
+//
+//  TODO(cpu): support not fully implemented yet for unicode string and will
+//  probably add other types as well.
+class ParameterSet {
+ public:
+  ParameterSet() : real_type_(INVALID_TYPE), address_(NULL) {}
+
+  // Retrieve the stored parameter. If the type does not match ulong fail.
+  bool Get(unsigned long* destination) const {
+    if (ULONG_TYPE != real_type_) {
+      return false;
+    }
+    *destination = Void2TypePointerCopy<unsigned long>();
+    return true;
+  }
+
+  // Retrieve the stored parameter. If the type does not match void* fail.
+  bool Get(const void** destination) const {
+    if (VOIDPTR_TYPE != real_type_) {
+      return false;
+    }
+    *destination = Void2TypePointerCopy<void*>();
+    return true;
+  }
+
+  // Retrieve the stored parameter. If the type does not match wchar_t* fail.
+  bool Get(const wchar_t** destination) const {
+    if (WCHAR_TYPE != real_type_) {
+      return false;
+    }
+    *destination = Void2TypePointerCopy<const wchar_t*>();
+    return true;
+  }
+
+  // False if the parameter is not properly initialized.
+  bool IsValid() const {
+    return INVALID_TYPE != real_type_;
+  }
+
+ protected:
+  // The constructor can only be called by derived types, which should
+  // safely provide the real_type and the address of the argument.
+  ParameterSet(ArgType real_type, const void* address)
+      : real_type_(real_type), address_(address) {
+  }
+
+ private:
+  // This template provides the same functionality as bits_cast but
+  // it works with pointer while the former works only with references.
+  template <typename T>
+  T Void2TypePointerCopy() const {
+    return *(reinterpret_cast<const T*>(address_));
+  }
+
+  ArgType real_type_;
+  const void* address_;
+};
+
+// To safely infer the type, we use a set of template specializations
+// in ParameterSetEx with a template function ParamPickerMake to do the
+// parameter type deduction.
+
+// Base template class. Not implemented so using unsupported types should
+// fail to compile.
+template <typename T>
+class ParameterSetEx : public ParameterSet {
+ public:
+  ParameterSetEx(const void* address);
+};
+
+template<>
+class ParameterSetEx<void const*> : public ParameterSet {
+ public:
+  ParameterSetEx(const void* address)
+      : ParameterSet(VOIDPTR_TYPE, address) {}
+};
+
+template<>
+class ParameterSetEx<void*> : public ParameterSet {
+ public:
+  ParameterSetEx(const void* address)
+      : ParameterSet(VOIDPTR_TYPE, address) {}
+};
+
+
+template<>
+class ParameterSetEx<wchar_t*> : public ParameterSet {
+ public:
+  ParameterSetEx(const void* address)
+      : ParameterSet(WCHAR_TYPE, address) {}
+};
+
+template<>
+class ParameterSetEx<wchar_t const*> : public ParameterSet {
+ public:
+  ParameterSetEx(const void* address)
+      : ParameterSet(WCHAR_TYPE, address) {}
+};
+
+
+template<>
+class ParameterSetEx<unsigned long> : public ParameterSet {
+ public:
+  ParameterSetEx(const void* address)
+      : ParameterSet(ULONG_TYPE, address) {}
+};
+
+template<>
+class ParameterSetEx<UNICODE_STRING> : public ParameterSet {
+ public:
+  ParameterSetEx(const void* address)
+      : ParameterSet(UNISTR_TYPE, address) {}
+};
+
+template <typename T>
+ParameterSet ParamPickerMake(T& parameter) {
+  return ParameterSetEx<T>(&parameter);
+};
+
+struct CountedParameterSetBase {
+  int count;
+  ParameterSet parameters[1];
+};
+
+// This template defines the actual list of policy parameters for a given
+// interception.
+// Warning: This template stores the address to the actual variables, in
+// other words, the values are not copied.
+template <typename T>
+struct CountedParameterSet {
+  CountedParameterSet() : count(T::PolParamLast) {}
+
+  ParameterSet& operator[](typename T::Args n) {
+    return parameters[n];
+  }
+
+  CountedParameterSetBase* GetBase() {
+    return reinterpret_cast<CountedParameterSetBase*>(this);
+  }
+
+  int count;
+  ParameterSet parameters[T::PolParamLast];
+};
+
+}  // namespace sandbox
+
+#endif  // SANDBOX_SRC_POLICY_ENGINE_PARAMS_H__