The Tor Browser: security/sandbox/win/src/policy_engine

security/sandbox/win/src/policy_engine_opcodes.h@b8a032363ba2 (annotated)

security/sandbox/win/src/policy_engine_opcodes.h

Thu, 22 Jan 2015 13:21:57 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Thu, 22 Jan 2015 13:21:57 +0100
branch: TOR_BUG_9701
changeset 15: b8a032363ba2
permissions: -rw-r--r--

Incorporate requested changes from Mozilla in review:
https://bugzilla.mozilla.org/show_bug.cgi?id=1123480#c6

 // Copyright (c) 2010 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 #ifndef SANDBOX_WIN_SRC_POLICY_ENGINE_OPCODES_H_
 #define SANDBOX_WIN_SRC_POLICY_ENGINE_OPCODES_H_
 #include "sandbox/win/src/policy_engine_params.h"
 #include "base/basictypes.h"
 // The low-level policy is implemented using the concept of policy 'opcodes'.
 // An opcode is a structure that contains enough information to perform one
 // comparison against one single input parameter. For example, an opcode can
 // encode just one of the following comparison:
 //
 // - Is input parameter 3 not equal to NULL?
 // - Does input parameter 2 start with L"c:\\"?
 // - Is input parameter 5, bit 3 is equal 1?
 //
 // Each opcode is in fact equivalent to a function invocation where all
 // the parameters are known by the opcode except one. So say you have a
 // function of this form:
 //      bool fn(a, b, c, d)  with 4 arguments
 //
 // Then an opcode is:
 //      op(fn, b, c, d)
 // Which stores the function to call and its 3 last arguments
 //
 // Then and opcode evaluation is:
 //      op.eval(a)  ------------------------> fn(a,b,c,d)
 //                        internally calls
 //
 // The idea is that complex policy rules can be split into streams of
 // opcodes which are evaluated in sequence. The evaluation is done in
 // groups of opcodes that have N comparison opcodes plus 1 action opcode:
 //
 // [comparison 1][comparison 2]...[comparison N][action][comparison 1]...
 //    ----- evaluation order----------->
 //
 // Each opcode group encodes one high-level policy rule. The rule applies
 // only if all the conditions on the group evaluate to true. The action
 // opcode contains the policy outcome for that particular rule.
 //
 // Note that this header contains the main building blocks of low-level policy
 // but not the low level policy class.
 namespace sandbox {
 // These are the possible policy outcomes. Note that some of them might
 // not apply and can be removed. Also note that The following values only
 // specify what to do, not how to do it and it is acceptable given specific
 // cases to ignore the policy outcome.
 enum EvalResult {
   // Comparison opcode values:
   EVAL_TRUE,   // Opcode condition evaluated true.
   EVAL_FALSE,  // Opcode condition evaluated false.
   EVAL_ERROR,  // Opcode condition generated an error while evaluating.
   // Action opcode values:
   ASK_BROKER,  // The target must generate an IPC to the broker. On the broker
                // side, this means grant access to the resource.
   DENY_ACCESS,   // No access granted to the resource.
   GIVE_READONLY,  // Give readonly access to the resource.
   GIVE_ALLACCESS,  // Give full access to the resource.
   GIVE_CACHED,  // IPC is not required. Target can return a cached handle.
   GIVE_FIRST,  // TODO(cpu)
   SIGNAL_ALARM,  // Unusual activity. Generate an alarm.
   FAKE_SUCCESS,  // Do not call original function. Just return 'success'.
   FAKE_ACCESS_DENIED,  // Do not call original function. Just return 'denied'
                        // and do not do IPC.
   TERMINATE_PROCESS,  // Destroy target process. Do IPC as well.
 };
 // The following are the implemented opcodes.
 enum OpcodeID {
   OP_ALWAYS_FALSE,  // Evaluates to false (EVAL_FALSE).
   OP_ALWAYS_TRUE,  // Evaluates to true (EVAL_TRUE).
   OP_NUMBER_MATCH,  // Match a 32-bit integer as n == a.
   OP_ULONG_MATCH_RANGE,  // Match an ulong integer as a <= n <= b.
   OP_ULONG_AND_MATCH,  // Match using bitwise AND; as in: n & a != 0.
   OP_WSTRING_MATCH,  // Match a string for equality.
   OP_ACTION  // Evaluates to an action opcode.
 };
 // Options that apply to every opcode. They are specified when creating
 // each opcode using OpcodeFactory::MakeOpXXXXX() family of functions
 // Do nothing special.
 const uint32 kPolNone = 0;
 // Convert EVAL_TRUE into EVAL_FALSE and vice-versa. This allows to express
 // negated conditions such as if ( a && !b).
 const uint32 kPolNegateEval = 1;
 // Zero the MatchContext context structure. This happens after the opcode
 // is evaluated.
 const uint32 kPolClearContext = 2;
 // Use OR when evaluating this set of opcodes. The policy evaluator by default
 // uses AND when evaluating. Very helpful when
 // used with kPolNegateEval. For example if you have a condition best expressed
 // as if(! (a && b && c)), the use of this flags allows it to be expressed as
 // if ((!a) || (!b) || (!c)).
 const uint32 kPolUseOREval = 4;
 // Keeps the evaluation state between opcode evaluations. This is used
 // for string matching where the next opcode needs to continue matching
 // from the last character position from the current opcode. The match
 // context is preserved across opcode evaluation unless an opcode specifies
 // as an option kPolClearContext.
 struct MatchContext {
   size_t position;
   uint32 options;
   MatchContext() {
     Clear();
   }
   void Clear() {
     position = 0;
     options = 0;
   }
 };
 // Models a policy opcode; that is a condition evaluation were all the
 // arguments but one are stored in objects of this class. Use OpcodeFactory
 // to create objects of this type.
 // This class is just an implementation artifact and not exposed to the
 // API clients or visible in the intercepted service. Internally, an
 // opcode is just:
 //  - An integer that identifies the actual opcode.
 //  - An index to indicate which one is the input argument
 //  - An array of arguments.
 // While an OO hierarchy of objects would have been a natural choice, the fact
 // that 1) this code can execute before the CRT is loaded, presents serious
 // problems in terms of guarantees about the actual state of the vtables and
 // 2) because the opcode objects are generated in the broker process, we need to
 // use plain objects. To preserve some minimal type safety templates are used
 // when possible.
 class PolicyOpcode {
   friend class OpcodeFactory;
  public:
   // Evaluates the opcode. For a typical comparison opcode the return value
   // is EVAL_TRUE or EVAL_FALSE. If there was an error in the evaluation the
   // the return is EVAL_ERROR. If the opcode is an action opcode then the
   // return can take other values such as ASK_BROKER.
   // parameters: An array of all input parameters. This argument is normally
   // created by the macros POLPARAMS_BEGIN() POLPARAMS_END.
   // count: The number of parameters passed as first argument.
   // match: The match context that is persisted across the opcode evaluation
   // sequence.
   EvalResult Evaluate(const ParameterSet* parameters, size_t count,
                       MatchContext* match);
   // Retrieves a stored argument by index. Valid index values are
   // from 0 to < kArgumentCount.
   template <typename T>
   void GetArgument(size_t index, T* argument) const {
     COMPILE_ASSERT(sizeof(T) <= sizeof(arguments_[0]), invalid_size);
     *argument = *reinterpret_cast<const T*>(&arguments_[index].mem);
   }
   // Sets a stored argument by index. Valid index values are
   // from 0 to < kArgumentCount.
   template <typename T>
   void SetArgument(size_t index, const T& argument) {
     COMPILE_ASSERT(sizeof(T) <= sizeof(arguments_[0]), invalid_size);
     *reinterpret_cast<T*>(&arguments_[index].mem) = argument;
   }
   // Retrieves the actual address of an string argument. When using
   // GetArgument() to retrieve an index that contains a string, the returned
   // value is just an offset to the actual string.
   // index: the stored string index. Valid values are from 0
   // to < kArgumentCount.
   const wchar_t* GetRelativeString(size_t index) const {
     ptrdiff_t str_delta = 0;
     GetArgument(index, &str_delta);
     const char* delta = reinterpret_cast<const char*>(this) + str_delta;
     return reinterpret_cast<const wchar_t*>(delta);
   }
   // Returns true if this opcode is an action opcode without actually
   // evaluating it. Used to do a quick scan forward to the next opcode group.
   bool IsAction() const {
     return (OP_ACTION == opcode_id_);
   };
   // Returns the opcode type.
   OpcodeID GetID() const {
     return opcode_id_;
   }
   // Returns the stored options such as kPolNegateEval and others.
   uint32 GetOptions() const {
     return options_;
   }
   // Sets the stored options such as kPolNegateEval.
   void SetOptions(int16 options) {
     options_ = options;
   }
  private:
   static const size_t kArgumentCount = 4;  // The number of supported argument.
   struct OpcodeArgument {
     UINT_PTR mem;
   };
   // Better define placement new in the class instead of relying on the
   // global definition which seems to be fubared.
   void* operator new(size_t, void* location) {
     return location;
   }
   // Helper function to evaluate the opcode. The parameters have the same
   // meaning that in Evaluate().
   EvalResult EvaluateHelper(const ParameterSet* parameters,
                            MatchContext* match);
   OpcodeID opcode_id_;
   int16 parameter_;
   int16 options_;
   OpcodeArgument arguments_[PolicyOpcode::kArgumentCount];
 };
 enum StringMatchOptions {
   CASE_SENSITIVE = 0,      // Pay or Not attention to the case as defined by
   CASE_INSENSITIVE = 1,    // RtlCompareUnicodeString windows API.
   EXACT_LENGHT = 2         // Don't do substring match. Do full string match.
 };
 // Opcodes that do string comparisons take a parameter that is the starting
 // position to perform the comparison so we can do substring matching. There
 // are two special values:
 //
 // Start from the current position and compare strings advancing forward until
 // a match is found if any. Similar to CRT strstr().
 const int  kSeekForward = -1;
 // Perform a match with the end of the string. It only does a single comparison.
 const int  kSeekToEnd = 0xfffff;
 // A PolicyBuffer is a variable size structure that contains all the opcodes
 // that are to be created or evaluated in sequence.
 struct PolicyBuffer {
   size_t opcode_count;
   PolicyOpcode opcodes[1];
 };
 // Helper class to create any opcode sequence. This class is normally invoked
 // only by the high level policy module or when you need to handcraft a special
 // policy.
 // The factory works by creating the opcodes using a chunk of memory given
 // in the constructor. The opcodes themselves are allocated from the beginning
 // (top) of the memory, while any string that an opcode needs is allocated from
 // the end (bottom) of the memory.
 //
 // In essence:
 //
 //   low address ---> [opcode 1]
 //                    [opcode 2]
 //                    [opcode 3]
 //                    |        | <--- memory_top_
 //                    | free   |
 //                    |        |
 //                    |        | <--- memory_bottom_
 //                    [string 1]
 //   high address --> [string 2]
 //
 // Note that this class does not keep track of the number of opcodes made and
 // it is designed to be a building block for low-level policy.
 //
 // Note that any of the MakeOpXXXXX member functions below can return NULL on
 // failure. When that happens opcode sequence creation must be aborted.
 class OpcodeFactory {
  public:
   // memory: base pointer to a chunk of memory where the opcodes are created.
   // memory_size: the size in bytes of the memory chunk.
   OpcodeFactory(char* memory, size_t memory_size)
       : memory_top_(memory) {
     memory_bottom_ = &memory_top_[memory_size];
   }
   // policy: contains the raw memory where the opcodes are created.
   // memory_size: contains the actual size of the policy argument.
   OpcodeFactory(PolicyBuffer* policy, size_t memory_size) {
     memory_top_ = reinterpret_cast<char*>(&policy->opcodes[0]);
     memory_bottom_ = &memory_top_[memory_size];
   }
   // Returns the available memory to make opcodes.
   size_t memory_size() const {
     return memory_bottom_ - memory_top_;
   }
   // Creates an OpAlwaysFalse opcode.
   PolicyOpcode* MakeOpAlwaysFalse(uint32 options);
   // Creates an OpAlwaysFalse opcode.
   PolicyOpcode* MakeOpAlwaysTrue(uint32 options);
   // Creates an OpAction opcode.
   // action: The action to return when Evaluate() is called.
   PolicyOpcode* MakeOpAction(EvalResult action, uint32 options);
   // Creates an OpNumberMatch opcode.
   // selected_param: index of the input argument. It must be a ulong or the
   // evaluation result will generate a EVAL_ERROR.
   // match: the number to compare against the selected_param.
   PolicyOpcode* MakeOpNumberMatch(int16 selected_param, unsigned long match,
                                   uint32 options);
   // Creates an OpNumberMatch opcode (void pointers are cast to numbers).
   // selected_param: index of the input argument. It must be an void* or the
   // evaluation result will generate a EVAL_ERROR.
   // match: the pointer numeric value to compare against selected_param.
   PolicyOpcode* MakeOpVoidPtrMatch(int16 selected_param, const void* match,
                                    uint32 options);
   // Creates an OpUlongMatchRange opcode using the memory passed in the ctor.
   // selected_param: index of the input argument. It must be a ulong or the
   // evaluation result will generate a EVAL_ERROR.
   // lower_bound, upper_bound: the range to compare against selected_param.
   PolicyOpcode* MakeOpUlongMatchRange(int16 selected_param,
                                       unsigned long lower_bound,
                                       unsigned long upper_bound,
                                       uint32 options);
   // Creates an OpWStringMatch opcode using the raw memory passed in the ctor.
   // selected_param: index of the input argument. It must be a wide string
   // pointer or the evaluation result will generate a EVAL_ERROR.
   // match_str: string to compare against selected_param.
   // start_position: when its value is from 0 to < 0x7fff it indicates an
   // offset from the selected_param string where to perform the comparison. If
   // the value is SeekForward  then a substring search is performed. If the
   // value is SeekToEnd the comparison is performed against the last part of
   // the selected_param string.
   // Note that the range in the position (0 to 0x7fff) is dictated by the
   // current implementation.
   // match_opts: Indicates additional matching flags. Currently CaseInsensitive
   // is supported.
   PolicyOpcode* MakeOpWStringMatch(int16 selected_param,
                                    const wchar_t* match_str,
                                    int start_position,
                                    StringMatchOptions match_opts,
                                    uint32 options);
   // Creates an OpUlongAndMatch opcode using the raw memory passed in the ctor.
   // selected_param: index of the input argument. It must be ulong or the
   // evaluation result will generate a EVAL_ERROR.
   // match: the value to bitwise AND against selected_param.
   PolicyOpcode* MakeOpUlongAndMatch(int16 selected_param,
                                     unsigned long match,
                                     uint32 options);
  private:
   // Constructs the common part of every opcode. selected_param is the index
   // of the input param to use when evaluating the opcode. Pass -1 in
   // selected_param to indicate that no input parameter is required.
   PolicyOpcode* MakeBase(OpcodeID opcode_id, uint32 options,
                          int16 selected_param);
   // Allocates (and copies) a string (of size length) inside the buffer and
   // returns the displacement with respect to start.
   ptrdiff_t AllocRelative(void* start, const wchar_t* str, size_t lenght);
   // Points to the lowest currently available address of the memory
   // used to make the opcodes. This pointer increments as opcodes are made.
   char* memory_top_;
   // Points to the highest currently available address of the memory
   // used to make the opcodes. This pointer decrements as opcode strings are
   // allocated.
   char* memory_bottom_;
   DISALLOW_COPY_AND_ASSIGN(OpcodeFactory);
 };
 }  // namespace sandbox
 #endif  // SANDBOX_WIN_SRC_POLICY_ENGINE_OPCODES_H_

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security/sandbox/win/src/policy_engine_opcodes.h@b8a032363ba2 (annotated)

security/sandbox/win/src/policy_engine_opcodes.h