src/support/lockedpool.h

   1 // Copyright (c) 2016 The Bitcoin Core developers
   2 // Distributed under the MIT software license, see the accompanying
   3 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
   4
   5 #ifndef BITCOIN_SUPPORT_LOCKEDPOOL_H
   6 #define BITCOIN_SUPPORT_LOCKEDPOOL_H
   7
   8 #include <stdint.h>
   9 #include <list>
  10 #include <map>
  11 #include <mutex>
  12 #include <memory>
  13
  14 /**
  15  * OS-dependent allocation and deallocation of locked/pinned memory pages.
  16  * Abstract base class.
  17  */
  18 class LockedPageAllocator
  19 {
  20 public:
  21     virtual ~LockedPageAllocator() {}
  22     /** Allocate and lock memory pages.
  23      * If len is not a multiple of the system page size, it is rounded up.
  24      * Returns 0 in case of allocation failure.
  25      *
  26      * If locking the memory pages could not be accomplished it will still
  27      * return the memory, however the lockingSuccess flag will be false.
  28      * lockingSuccess is undefined if the allocation fails.
  29      */
  30     virtual void* AllocateLocked(size_t len, bool *lockingSuccess) = 0;
  31
  32     /** Unlock and free memory pages.
  33      * Clear the memory before unlocking.
  34      */
  35     virtual void FreeLocked(void* addr, size_t len) = 0;
  36
  37     /** Get the total limit on the amount of memory that may be locked by this
  38      * process, in bytes. Return size_t max if there is no limit or the limit
  39      * is unknown. Return 0 if no memory can be locked at all.
  40      */
  41     virtual size_t GetLimit() = 0;
  42 };
  43
  44 /* An arena manages a contiguous region of memory by dividing it into
  45  * chunks.
  46  */
  47 class Arena
  48 {
  49 public:
  50     Arena(void *base, size_t size, size_t alignment);
  51     virtual ~Arena();
  52
  53     Arena(const Arena& other) = delete; // non construction-copyable
  54     Arena& operator=(const Arena&) = delete; // non copyable
  55
  56     /** Memory statistics. */
  57     struct Stats
  58     {
  59         size_t used;
  60         size_t free;
  61         size_t total;
  62         size_t chunks_used;
  63         size_t chunks_free;
  64     };
  65
  66     /** Allocate size bytes from this arena.
  67      * Returns pointer on success, or 0 if memory is full or
  68      * the application tried to allocate 0 bytes.
  69      */
  70     void* alloc(size_t size);
  71
  72     /** Free a previously allocated chunk of memory.
  73      * Freeing the zero pointer has no effect.
  74      * Raises std::runtime_error in case of error.
  75      */
  76     void free(void *ptr);
  77
  78     /** Get arena usage statistics */
  79     Stats stats() const;
  80
  81 #ifdef ARENA_DEBUG
  82     void walk() const;
  83 #endif
  84
  85     /** Return whether a pointer points inside this arena.
  86      * This returns base <= ptr < (base+size) so only use it for (inclusive)
  87      * chunk starting addresses.
  88      */
  89     bool addressInArena(void *ptr) const { return ptr >= base && ptr < end; }
  90 private:
  91     /** Map of chunk address to chunk information. This class makes use of the
  92      * sorted order to merge previous and next chunks during deallocation.
  93      */
  94     std::map<char*, size_t> chunks_free;
  95     std::map<char*, size_t> chunks_used;
  96     /** Base address of arena */
  97     char* base;
  98     /** End address of arena */
  99     char* end;
 100     /** Minimum chunk alignment */
 101     size_t alignment;
 102 };
 103
 104 /** Pool for locked memory chunks.
 105  *
 106  * To avoid sensitive key data from being swapped to disk, the memory in this pool
 107  * is locked/pinned.
 108  *
 109  * An arena manages a contiguous region of memory. The pool starts out with one arena
 110  * but can grow to multiple arenas if the need arises.
 111  *
 112  * Unlike a normal C heap, the administrative structures are separate from the managed
 113  * memory. This has been done as the sizes and bases of objects are not in themselves sensitive
 114  * information, as to conserve precious locked memory. In some operating systems
 115  * the amount of memory that can be locked is small.
 116  */
 117 class LockedPool
 118 {
 119 public:
 120     /** Size of one arena of locked memory. This is a compromise.
 121      * Do not set this too low, as managing many arenas will increase
 122      * allocation and deallocation overhead. Setting it too high allocates
 123      * more locked memory from the OS than strictly necessary.
 124      */
 125     static const size_t ARENA_SIZE = 256*1024;
 126     /** Chunk alignment. Another compromise. Setting this too high will waste
 127      * memory, setting it too low will facilitate fragmentation.
 128      */
 129     static const size_t ARENA_ALIGN = 16;
 130
 131     /** Callback when allocation succeeds but locking fails.
 132      */
 133     typedef bool (*LockingFailed_Callback)();
 134
 135     /** Memory statistics. */
 136     struct Stats
 137     {
 138         size_t used;
 139         size_t free;
 140         size_t total;
 141         size_t locked;
 142         size_t chunks_used;
 143         size_t chunks_free;
 144     };
 145
 146     /** Create a new LockedPool. This takes ownership of the MemoryPageLocker,
 147      * you can only instantiate this with LockedPool(std::move(...)).
 148      *
 149      * The second argument is an optional callback when locking a newly allocated arena failed.
 150      * If this callback is provided and returns false, the allocation fails (hard fail), if
 151      * it returns true the allocation proceeds, but it could warn.
 152      */
 153     explicit LockedPool(std::unique_ptr<LockedPageAllocator> allocator, LockingFailed_Callback lf_cb_in = nullptr);
 154     ~LockedPool();
 155
 156     LockedPool(const LockedPool& other) = delete; // non construction-copyable
 157     LockedPool& operator=(const LockedPool&) = delete; // non copyable
 158
 159     /** Allocate size bytes from this arena.
 160      * Returns pointer on success, or 0 if memory is full or
 161      * the application tried to allocate 0 bytes.
 162      */
 163     void* alloc(size_t size);
 164
 165     /** Free a previously allocated chunk of memory.
 166      * Freeing the zero pointer has no effect.
 167      * Raises std::runtime_error in case of error.
 168      */
 169     void free(void *ptr);
 170
 171     /** Get pool usage statistics */
 172     Stats stats() const;
 173 private:
 174     std::unique_ptr<LockedPageAllocator> allocator;
 175
 176     /** Create an arena from locked pages */
 177     class LockedPageArena: public Arena
 178     {
 179     public:
 180         LockedPageArena(LockedPageAllocator *alloc_in, void *base_in, size_t size, size_t align);
 181         ~LockedPageArena();
 182     private:
 183         void *base;
 184         size_t size;
 185         LockedPageAllocator *allocator;
 186     };
 187
 188     bool new_arena(size_t size, size_t align);
 189
 190     std::list<LockedPageArena> arenas;
 191     LockingFailed_Callback lf_cb;
 192     size_t cumulative_bytes_locked;
 193     /** Mutex protects access to this pool's data structures, including arenas.
 194      */
 195     mutable std::mutex mutex;
 196 };
 197
 198 /**
 199  * Singleton class to keep track of locked (ie, non-swappable) memory, for use in
 200  * std::allocator templates.
 201  *
 202  * Some implementations of the STL allocate memory in some constructors (i.e., see
 203  * MSVC's vector<T> implementation where it allocates 1 byte of memory in the allocator.)
 204  * Due to the unpredictable order of static initializers, we have to make sure the
 205  * LockedPoolManager instance exists before any other STL-based objects that use
 206  * secure_allocator are created. So instead of having LockedPoolManager also be
 207  * static-initialized, it is created on demand.
 208  */
 209 class LockedPoolManager : public LockedPool
 210 {
 211 public:
 212     /** Return the current instance, or create it once */
 213     static LockedPoolManager& Instance()
 214     {
 215         std::call_once(LockedPoolManager::init_flag, LockedPoolManager::CreateInstance);
 216         return *LockedPoolManager::_instance;
 217     }
 218
 219 private:
 220     explicit LockedPoolManager(std::unique_ptr<LockedPageAllocator> allocator);
 221
 222     /** Create a new LockedPoolManager specialized to the OS */
 223     static void CreateInstance();
 224     /** Called when locking fails, warn the user here */
 225     static bool LockingFailed();
 226
 227     static LockedPoolManager* _instance;
 228     static std::once_flag init_flag;
 229 };
 230
 231 #endif // BITCOIN_SUPPORT_LOCKEDPOOL_H