allocators.h

#ifndef ALLOCATORS_H
#define ALLOCATORS_H

#include <boost/thread/mutex.hpp>
#include <boost/thread/once.hpp>

#include <openssl/crypto.h> // for OPENSSL_cleanse()

#include "zero_after_free_allocator.h"
#include <vector>

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;
};

class MemoryPageLocker
{
public:
    bool Lock(const void* addr, size_t len);
    bool Unlock(const void* addr, size_t len);
};

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)
{
    OPENSSL_cleanse((void*)(&t), sizeof(T));
    LockedPageManager::Instance().UnlockRange((void*)(&t), sizeof(T));
}

//
// Allocator that locks its contents from being paged
// out of memory and clears its contents before deletion.
//
template <typename T>
struct secure_allocator : public std::allocator<T> {
    // MSVC8 default copy constructor is broken
    typedef std::allocator<T> base;
    typedef typename base::size_type size_type;
    typedef typename base::difference_type difference_type;
    typedef typename base::pointer pointer;
    typedef typename base::const_pointer const_pointer;
    typedef typename base::reference reference;
    typedef typename base::const_reference const_reference;
    typedef typename base::value_type value_type;
    secure_allocator() throw() {}
    secure_allocator(const secure_allocator& a) throw() : base(a) {}
    template <typename U>
    secure_allocator(const secure_allocator<U>& a) throw() : base(a)
    {
    }
    ~secure_allocator() throw() {}
    template <typename _Other>
    struct rebind {
        typedef secure_allocator<_Other> other;
    };

    T* allocate(std::size_t n, const void* hint = 0)
    {
        T* p;
        p = std::allocator<T>::allocate(n, hint);
        if (p != NULL)
            LockedPageManager::Instance().LockRange(p, sizeof(T) * n);
        return p;
    }

    void deallocate(T* p, std::size_t n)
    {
        if (p != NULL) {
            OPENSSL_cleanse(p, sizeof(T) * n);
            LockedPageManager::Instance().UnlockRange(p, sizeof(T) * n);
        }
        std::allocator<T>::deallocate(p, n);
    }
};

// Byte-vector that clears its contents before deletion.
typedef std::vector<char, zero_after_free_allocator<char> > CSerializeData;

#endif // ALLOCATORS_H