OLD | NEW |
---|---|
(Empty) | |
1 // Copyright (c) 2015 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 #ifndef BASE_MEMORY_SHARED_MEMORY_ALLOCATOR_H_ | |
6 #define BASE_MEMORY_SHARED_MEMORY_ALLOCATOR_H_ | |
7 | |
8 #include <stdint.h> | |
9 | |
10 #include "base/atomicops.h" | |
11 #include "base/base_export.h" | |
12 #include "base/macros.h" | |
13 | |
14 namespace base { | |
15 | |
16 // Simple allocator for pieces of a memory block that may be shared across | |
17 // multiple processes. | |
18 // | |
19 // This class provides for thread-secure (i.e. safe against other threads | |
20 // or processes that may be compromised and thus have malicious intent) | |
21 // allocation of memory within a designated block and also a mechanism by | |
22 // which other threads can learn of the allocations with any additional | |
23 // shared information. | |
24 // | |
25 // There is (currently) no way to release an allocated block of data because | |
26 // doing so would risk invalidating pointers held by other processes and | |
27 // greatly complicate the allocation algorithm. | |
28 // | |
29 // Construction of this object can accept new, clean (i.e. zeroed) memory | |
30 // or previously initialized memory. In the first case, construction must | |
31 // be allowed to complete before letting other allocators attach to the same | |
32 // segment. In other words, don't share the segment until at least one | |
33 // allocator has been attached to it. | |
34 // | |
35 // It should be noted that memory doesn't need to actually have zeros written | |
36 // throughout; it just needs to read as zero until something diffferent is | |
37 // written to a location. This is an important distinction as it supports the | |
38 // use-case of non-pinned memory, such as from a demand-allocated region by | |
39 // the OS or a memory-mapped file that auto-grows from a starting size of zero. | |
40 class BASE_EXPORT SharedMemoryAllocator { | |
41 public: | |
42 typedef int32_t Reference; | |
43 | |
44 // Internal state information when iterating over memory allocations. | |
45 struct Iterator { | |
46 Reference last; | |
47 uint32_t niter; | |
48 }; | |
49 | |
50 // Returned information about the internal state of the heap. | |
51 struct MemoryInfo { | |
52 size_t total; | |
53 size_t free; | |
54 }; | |
55 | |
56 enum : uint32_t { | |
57 kTypeIdAny = 0 // Match any type-id inside GetAsObject(). | |
58 }; | |
59 | |
60 // The allocator operates on any arbitrary block of memory. Creation and | |
61 // sharing of that block with another process is the responsibility of the | |
62 // caller. The allocator needs to know only the block's |base| address, the | |
63 // total |size| of the block, and any internal |page| size (zero if not | |
64 // paged) across which allocations should not span. | |
65 // | |
66 // SharedMemoryAllocator does NOT take ownership of this memory block. The | |
67 // caller must manage it and ensure it stays available throughout the lifetime | |
68 // of this object. | |
69 // | |
70 // Memory segments for sharing must have had an allocator attached to them | |
71 // before actually being shared. If the memory segment was just created, it | |
72 // should be zeroed. If it was an existing segment, the values here will | |
73 // be compared to copies stored in the shared segment as a guard against | |
74 // corruption. | |
75 SharedMemoryAllocator(void* base, size_t size, size_t page_size); | |
76 ~SharedMemoryAllocator(); | |
77 | |
78 // Get an object referenced by a |ref|. For safety reasons, the |type_id| | |
79 // code and size-of(|T|) are compared to ensure the reference is valid | |
80 // and cannot return an object outside of the memory segment. A |type_id| of | |
81 // zero will match any though the size is still checked. NULL is returned | |
82 // if any problem is detected, such as corrupted storage or incorrect | |
83 // parameters. Callers MUST check that the returned value is not-null EVERY | |
84 // TIME before accessing it or risk crashing! Once dereferenced, the pointer | |
mdempsky
2015/11/10 19:47:56
I'm a little unclear on these last two sentences.
| |
85 // is safe to reuse forever. | |
86 // | |
87 // NOTE: Though this method will guarantee that an object of the specified | |
88 // type can be accessed without going outside the bounds of the memory | |
89 // segment, it makes no guarantees of the validity of the data within the | |
90 // object itself. If it is expected that the contents of the segment could | |
91 // be compromised with malicious intent, the object must be hardened as well. | |
92 template <typename T> | |
93 T* GetAsObject(Reference ref, uint32_t type_id) { | |
94 return static_cast<T*>(GetBlockData(ref, type_id, sizeof(T))); | |
95 } | |
96 | |
97 // Get the number of bytes allocated to a block. This is useful when storing | |
98 // arrays in order to validate the ending boundary. The returned value will | |
99 // include any padding added to achieve the required alignment and so could | |
100 // be larger than given in the original Allocate() request. | |
101 size_t GetAllocSize(Reference ref); | |
102 | |
103 // Reserve space in the memory segment of the desired |size| and |type_id|. | |
104 // A return value of zero indicates the allocation failed, otherwise the | |
105 // returned reference can be used by any process to get a real pointer via | |
106 // the GetAsObject() call. | |
107 int32_t Allocate(size_t size, uint32_t type_id); | |
108 | |
109 // Allocated objects can be added to an internal list that can then be | |
110 // iterated over by other processes. If an allocated object can be found | |
111 // another way, such as by having its reference within a different object | |
112 // that will be made iterable, then this call is not necessary. This always | |
113 // succeeds unless corruption is detected; check IsCorrupted() to find out. | |
114 void MakeIterable(Reference ref); | |
115 | |
116 // Get the information about the amount of free space in the allocator. The | |
117 // amount of free space should be treated as approximate due to extras from | |
118 // alignment and metadata. Concurrent allocations from other threads will | |
119 // also make the true amount less than what is reported. | |
120 void GetMemoryInfo(MemoryInfo* meminfo); | |
121 | |
122 // Iterating uses a |state| structure (initialized by CreateIterator) and | |
mdempsky
2015/11/10 19:47:56
nit: I think "uses an |Iterator| structure" is mea
| |
123 // returns both the reference to the object as well as the |type_id| of | |
124 // that object. A zero return value indicates there are currently no more | |
125 // objects to be found but future attempts can be made without having to | |
126 // reset the iterator to "first". | |
127 void CreateIterator(Iterator* state); | |
128 int32_t GetNextIterable(Iterator* state, uint32_t* type_id); | |
mdempsky
2015/11/10 19:47:55
Should the return type be Reference?
| |
129 | |
130 // If there is some indication that the shared memory has become corrupted, | |
131 // calling this will attempt to prevent further damage by indicating to | |
132 // all processes that something is not as expected. | |
133 void SetCorrupt(); | |
134 | |
135 // This can be called to determine if corruption has been detected in the | |
136 // shared segment, possibly my a malicious actor. Once detected, future | |
mdempsky
2015/11/10 19:47:56
typo: s/my/by/
| |
137 // allocations will fail and iteration may not locate all objects. | |
138 bool IsCorrupt(); | |
139 | |
140 // Flag set if an allocation has failed because memory was full. | |
141 bool IsFull(); | |
142 | |
143 private: | |
144 struct SharedMetadata; | |
145 struct BlockHeader; | |
146 | |
147 // The shared metadata is always located at the top of the shared memory. | |
148 // This convenience function eliminates constant casting of the base pointer | |
mdempsky
2015/11/10 19:47:56
nit: Say "repeated casting" since "constant castin
| |
149 // within the code. | |
150 SharedMetadata* shared_meta() { | |
151 return reinterpret_cast<SharedMetadata*>(mem_base_); | |
152 } | |
153 | |
154 BlockHeader* GetBlock(Reference ref, uint32_t type_id, int32_t size, | |
155 bool queue_ok, bool free_ok); | |
156 void* GetBlockData(Reference ref, uint32_t type_id, int32_t size); | |
157 | |
158 char* mem_base_; // Same. (char because sizeof guaranteed 1) | |
mdempsky
2015/11/10 19:47:56
Same as what?
| |
159 int32_t mem_size_; // Size of entire memory segment. | |
160 int32_t mem_page_; // Page size allocations shouldn't cross. | |
161 subtle::Atomic32 corrupted_; // Local version of "corrupted" flag. | |
162 | |
163 DISALLOW_COPY_AND_ASSIGN(SharedMemoryAllocator); | |
164 }; | |
165 | |
166 } // namespace base | |
167 | |
168 #endif // BASE_MEMORY_SHARED_MEMORY_ALLOCATOR_H_ | |
OLD | NEW |