allocators: split allocators and pagelocker

Pagelocker is only needed for secure (usually wallet) operations, so don't make
the zero-after-free allocator depend on it.

1 files changed, 178 insertions, 0 deletions

diff --git a/src/support/pagelocker.h b/src/support/pagelocker.h
new file mode 100644
index 0000000000..964be1aec4
--- /dev/null
+++ b/src/support/pagelocker.h
@@ -0,0 +1,178 @@
+// Copyright (c) 2009-2010 Satoshi Nakamoto
+// Copyright (c) 2009-2013 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef BITCOIN_ALLOCATORS_PAGELOCKER_H
+#define BITCOIN_ALLOCATORS_PAGELOCKER_H
+
+#include "support/cleanse.h"
+
+#include <map>
+
+#include <boost/thread/mutex.hpp>
+#include <boost/thread/once.hpp>
+
+/**
+ * Thread-safe class to keep track of locked (ie, non-swappable) memory pages.
+ *
+ * Memory locks do not stack, that is, pages which have been locked several times by calls to mlock()
+ * will be unlocked by a single call to munlock(). This can result in keying material ending up in swap when
+ * those functions are used naively. This class simulates stacking memory locks by keeping a counter per page.
+ *
+ * @note By using a map from each page base address to lock count, this class is optimized for
+ * small objects that span up to a few pages, mostly smaller than a page. To support large allocations,
+ * something like an interval tree would be the preferred data structure.
+ */
+template <class Locker>
+class LockedPageManagerBase
+{
+public:
+    LockedPageManagerBase(size_t page_size) : page_size(page_size)
+    {
+        // Determine bitmask for extracting page from address
+        assert(!(page_size & (page_size - 1))); // size must be power of two
+        page_mask = ~(page_size - 1);
+    }
+
+    ~LockedPageManagerBase()
+    {
+        assert(this->GetLockedPageCount() == 0);
+    }
+
+
+    // For all pages in affected range, increase lock count
+    void LockRange(void* p, size_t size)
+    {
+        boost::mutex::scoped_lock lock(mutex);
+        if (!size)
+            return;
+        const size_t base_addr = reinterpret_cast<size_t>(p);
+        const size_t start_page = base_addr & page_mask;
+        const size_t end_page = (base_addr + size - 1) & page_mask;
+        for (size_t page = start_page; page <= end_page; page += page_size) {
+            Histogram::iterator it = histogram.find(page);
+            if (it == histogram.end()) // Newly locked page
+            {
+                locker.Lock(reinterpret_cast<void*>(page), page_size);
+                histogram.insert(std::make_pair(page, 1));
+            } else // Page was already locked; increase counter
+            {
+                it->second += 1;
+            }
+        }
+    }
+
+    // For all pages in affected range, decrease lock count
+    void UnlockRange(void* p, size_t size)
+    {
+        boost::mutex::scoped_lock lock(mutex);
+        if (!size)
+            return;
+        const size_t base_addr = reinterpret_cast<size_t>(p);
+        const size_t start_page = base_addr & page_mask;
+        const size_t end_page = (base_addr + size - 1) & page_mask;
+        for (size_t page = start_page; page <= end_page; page += page_size) {
+            Histogram::iterator it = histogram.find(page);
+            assert(it != histogram.end()); // Cannot unlock an area that was not locked
+            // Decrease counter for page, when it is zero, the page will be unlocked
+            it->second -= 1;
+            if (it->second == 0) // Nothing on the page anymore that keeps it locked
+            {
+                // Unlock page and remove the count from histogram
+                locker.Unlock(reinterpret_cast<void*>(page), page_size);
+                histogram.erase(it);
+            }
+        }
+    }
+
+    // Get number of locked pages for diagnostics
+    int GetLockedPageCount()
+    {
+        boost::mutex::scoped_lock lock(mutex);
+        return histogram.size();
+    }
+
+private:
+    Locker locker;
+    boost::mutex mutex;
+    size_t page_size, page_mask;
+    // map of page base address to lock count
+    typedef std::map<size_t, int> Histogram;
+    Histogram histogram;
+};
+
+
+/**
+ * OS-dependent memory page locking/unlocking.
+ * Defined as policy class to make stubbing for test possible.
+ */
+class MemoryPageLocker
+{
+public:
+    /** Lock memory pages.
+     * addr and len must be a multiple of the system page size
+     */
+    bool Lock(const void* addr, size_t len);
+    /** Unlock memory pages.
+     * addr and len must be a multiple of the system page size
+     */
+    bool Unlock(const void* addr, size_t len);
+};
+
+/**
+ * Singleton class to keep track of locked (ie, non-swappable) memory pages, for use in
+ * std::allocator templates.
+ *
+ * Some implementations of the STL allocate memory in some constructors (i.e., see
+ * MSVC's vector<T> implementation where it allocates 1 byte of memory in the allocator.)
+ * Due to the unpredictable order of static initializers, we have to make sure the
+ * LockedPageManager instance exists before any other STL-based objects that use
+ * secure_allocator are created. So instead of having LockedPageManager also be
+ * static-initialized, it is created on demand.
+ */
+class LockedPageManager : public LockedPageManagerBase<MemoryPageLocker>
+{
+public:
+    static LockedPageManager& Instance()
+    {
+        boost::call_once(LockedPageManager::CreateInstance, LockedPageManager::init_flag);
+        return *LockedPageManager::_instance;
+    }
+
+private:
+    LockedPageManager();
+
+    static void CreateInstance()
+    {
+        // Using a local static instance guarantees that the object is initialized
+        // when it's first needed and also deinitialized after all objects that use
+        // it are done with it.  I can think of one unlikely scenario where we may
+        // have a static deinitialization order/problem, but the check in
+        // LockedPageManagerBase's destructor helps us detect if that ever happens.
+        static LockedPageManager instance;
+        LockedPageManager::_instance = &instance;
+    }
+
+    static LockedPageManager* _instance;
+    static boost::once_flag init_flag;
+};
+
+//
+// Functions for directly locking/unlocking memory objects.
+// Intended for non-dynamically allocated structures.
+//
+template <typename T>
+void LockObject(const T& t)
+{
+    LockedPageManager::Instance().LockRange((void*)(&t), sizeof(T));
+}
+
+template <typename T>
+void UnlockObject(const T& t)
+{
+    memory_cleanse((void*)(&t), sizeof(T));
+    LockedPageManager::Instance().UnlockRange((void*)(&t), sizeof(T));
+}
+
+#endif // BITCOIN_ALLOCATORS_PAGELOCKER_H