Initial Vexta Core v0.1.0 release

src/support/allocators/secure.h

@@ -0,0 +1,63 @@
+// Copyright (c) 2009-2010 Satoshi Nakamoto
+// Copyright (c) 2009-2019 The Bitcoin Core developers
+// Copyright (c) 2014-2019 The DigiByte Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef DIGIBYTE_SUPPORT_ALLOCATORS_SECURE_H
+#define DIGIBYTE_SUPPORT_ALLOCATORS_SECURE_H
+
+#include <support/lockedpool.h>
+#include <support/cleanse.h>
+
+#include <string>
+
+//
+// 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() noexcept {}
+    secure_allocator(const secure_allocator& a) noexcept : base(a) {}
+    template <typename U>
+    secure_allocator(const secure_allocator<U>& a) noexcept : base(a)
+    {
+    }
+    ~secure_allocator() noexcept {}
+    template <typename _Other>
+    struct rebind {
+        typedef secure_allocator<_Other> other;
+    };
+
+    T* allocate(std::size_t n, const void* hint = 0)
+    {
+        T* allocation = static_cast<T*>(LockedPoolManager::Instance().alloc(sizeof(T) * n));
+        if (!allocation) {
+            throw std::bad_alloc();
+        }
+        return allocation;
+    }
+
+    void deallocate(T* p, std::size_t n)
+    {
+        if (p != nullptr) {
+            memory_cleanse(p, sizeof(T) * n);
+        }
+        LockedPoolManager::Instance().free(p);
+    }
+};
+
+// This is exactly like std::string, but with a custom allocator.
+typedef std::basic_string<char, std::char_traits<char>, secure_allocator<char> > SecureString;
+
+#endif // DIGIBYTE_SUPPORT_ALLOCATORS_SECURE_H

src/support/allocators/zeroafterfree.h

@@ -0,0 +1,49 @@
+// Copyright (c) 2009-2010 Satoshi Nakamoto
+// Copyright (c) 2009-2018 The Bitcoin Core developers
+// Copyright (c) 2014-2019 The DigiByte Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef DIGIBYTE_SUPPORT_ALLOCATORS_ZEROAFTERFREE_H
+#define DIGIBYTE_SUPPORT_ALLOCATORS_ZEROAFTERFREE_H
+
+#include <support/cleanse.h>
+
+#include <memory>
+#include <vector>
+
+template <typename T>
+struct zero_after_free_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;
+    zero_after_free_allocator() noexcept {}
+    zero_after_free_allocator(const zero_after_free_allocator& a) noexcept : base(a) {}
+    template <typename U>
+    zero_after_free_allocator(const zero_after_free_allocator<U>& a) noexcept : base(a)
+    {
+    }
+    ~zero_after_free_allocator() noexcept {}
+    template <typename _Other>
+    struct rebind {
+        typedef zero_after_free_allocator<_Other> other;
+    };
+
+    void deallocate(T* p, std::size_t n)
+    {
+        if (p != nullptr)
+            memory_cleanse(p, sizeof(T) * n);
+        std::allocator<T>::deallocate(p, n);
+    }
+};
+
+/** Byte-vector that clears its contents before deletion. */
+using SerializeData = std::vector<uint8_t, zero_after_free_allocator<uint8_t>>;
+
+#endif // DIGIBYTE_SUPPORT_ALLOCATORS_ZEROAFTERFREE_H

src/support/cleanse.cpp

@@ -0,0 +1,36 @@
+// Copyright (c) 2009-2010 Satoshi Nakamoto
+// Copyright (c) 2009-2020 The Bitcoin Core developers
+// Copyright (c) 2014-2020 The DigiByte Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <support/cleanse.h>
+
+#include <cstring>
+
+#if defined(_MSC_VER)
+#include <Windows.h> // For SecureZeroMemory.
+#endif
+
+void memory_cleanse(void *ptr, size_t len)
+{
+#if defined(_MSC_VER)
+    /* SecureZeroMemory is guaranteed not to be optimized out by MSVC. */
+    SecureZeroMemory(ptr, len);
+#else
+    std::memset(ptr, 0, len);
+
+    /* Memory barrier that scares the compiler away from optimizing out the memset.
+     *
+     * Quoting Adam Langley <agl@google.com> in commit ad1907fe73334d6c696c8539646c21b11178f20f
+     * in BoringSSL (ISC License):
+     *    As best as we can tell, this is sufficient to break any optimisations that
+     *    might try to eliminate "superfluous" memsets.
+     * This method is used in memzero_explicit() the Linux kernel, too. Its advantage is that it
+     * is pretty efficient because the compiler can still implement the memset() efficiently,
+     * just not remove it entirely. See "Dead Store Elimination (Still) Considered Harmful" by
+     * Yang et al. (USENIX Security 2017) for more background.
+     */
+    __asm__ __volatile__("" : : "r"(ptr) : "memory");
+#endif
+}

src/support/cleanse.h

@@ -0,0 +1,16 @@
+// Copyright (c) 2009-2010 Satoshi Nakamoto
+// Copyright (c) 2009-2020 The Bitcoin Core developers
+// Copyright (c) 2014-2020 The DigiByte Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef DIGIBYTE_SUPPORT_CLEANSE_H
+#define DIGIBYTE_SUPPORT_CLEANSE_H
+
+#include <stdlib.h>
+
+/** Secure overwrite a buffer (possibly containing secret data) with zero-bytes. The write
+ * operation will not be optimized out by the compiler. */
+void memory_cleanse(void *ptr, size_t len);
+
+#endif // DIGIBYTE_SUPPORT_CLEANSE_H

src/support/events.h

@@ -0,0 +1,57 @@
+// Copyright (c) 2009-2020 The Bitcoin Core developers
+// Copyright (c) 2014-2020 The DigiByte Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef DIGIBYTE_SUPPORT_EVENTS_H
+#define DIGIBYTE_SUPPORT_EVENTS_H
+
+#include <ios>
+#include <memory>
+
+#include <event2/event.h>
+#include <event2/http.h>
+
+#define MAKE_RAII(type) \
+/* deleter */\
+struct type##_deleter {\
+    void operator()(struct type* ob) {\
+        type##_free(ob);\
+    }\
+};\
+/* unique ptr typedef */\
+typedef std::unique_ptr<struct type, type##_deleter> raii_##type
+
+MAKE_RAII(event_base);
+MAKE_RAII(event);
+MAKE_RAII(evhttp);
+MAKE_RAII(evhttp_request);
+MAKE_RAII(evhttp_connection);
+
+inline raii_event_base obtain_event_base() {
+    auto result = raii_event_base(event_base_new());
+    if (!result.get())
+        throw std::runtime_error("cannot create event_base");
+    return result;
+}
+
+inline raii_event obtain_event(struct event_base* base, evutil_socket_t s, short events, event_callback_fn cb, void* arg) {
+    return raii_event(event_new(base, s, events, cb, arg));
+}
+
+inline raii_evhttp obtain_evhttp(struct event_base* base) {
+    return raii_evhttp(evhttp_new(base));
+}
+
+inline raii_evhttp_request obtain_evhttp_request(void(*cb)(struct evhttp_request *, void *), void *arg) {
+    return raii_evhttp_request(evhttp_request_new(cb, arg));
+}
+
+inline raii_evhttp_connection obtain_evhttp_connection_base(struct event_base* base, std::string host, uint16_t port) {
+    auto result = raii_evhttp_connection(evhttp_connection_base_new(base, nullptr, host.c_str(), port));
+    if (!result.get())
+        throw std::runtime_error("create connection failed");
+    return result;
+}
+
+#endif // DIGIBYTE_SUPPORT_EVENTS_H

src/support/lockedpool.cpp

@@ -0,0 +1,413 @@
+// Copyright (c) 2016-2020 The Bitcoin Core developers
+// Copyright (c) 2016-2020 The DigiByte Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <support/lockedpool.h>
+#include <support/cleanse.h>
+
+#if defined(HAVE_CONFIG_H)
+#include <config/vexta-config.h>
+#endif
+
+#ifdef WIN32
+#ifndef NOMINMAX
+#define NOMINMAX
+#endif
+#include <windows.h>
+#else
+#include <sys/mman.h> // for mmap
+#include <sys/resource.h> // for getrlimit
+#include <limits.h> // for PAGESIZE
+#include <unistd.h> // for sysconf
+#endif
+
+#include <algorithm>
+#include <stdexcept>
+#ifdef ARENA_DEBUG
+#include <iomanip>
+#include <iostream>
+#endif
+
+LockedPoolManager* LockedPoolManager::_instance = nullptr;
+
+/*******************************************************************************/
+// Utilities
+//
+/** Align up to power of 2 */
+static inline size_t align_up(size_t x, size_t align)
+{
+    return (x + align - 1) & ~(align - 1);
+}
+
+/*******************************************************************************/
+// Implementation: Arena
+
+Arena::Arena(void *base_in, size_t size_in, size_t alignment_in):
+    base(static_cast<char*>(base_in)), end(static_cast<char*>(base_in) + size_in), alignment(alignment_in)
+{
+    // Start with one free chunk that covers the entire arena
+    auto it = size_to_free_chunk.emplace(size_in, base);
+    chunks_free.emplace(base, it);
+    chunks_free_end.emplace(base + size_in, it);
+}
+
+Arena::~Arena()
+{
+}
+
+void* Arena::alloc(size_t size)
+{
+    // Round to next multiple of alignment
+    size = align_up(size, alignment);
+
+    // Don't handle zero-sized chunks
+    if (size == 0)
+        return nullptr;
+
+    // Pick a large enough free-chunk. Returns an iterator pointing to the first element that is not less than key.
+    // This allocation strategy is best-fit. According to "Dynamic Storage Allocation: A Survey and Critical Review",
+    // Wilson et. al. 1995, https://www.scs.stanford.edu/14wi-cs140/sched/readings/wilson.pdf, best-fit and first-fit
+    // policies seem to work well in practice.
+    auto size_ptr_it = size_to_free_chunk.lower_bound(size);
+    if (size_ptr_it == size_to_free_chunk.end())
+        return nullptr;
+
+    // Create the used-chunk, taking its space from the end of the free-chunk
+    const size_t size_remaining = size_ptr_it->first - size;
+    auto allocated = chunks_used.emplace(size_ptr_it->second + size_remaining, size).first;
+    chunks_free_end.erase(size_ptr_it->second + size_ptr_it->first);
+    if (size_ptr_it->first == size) {
+        // whole chunk is used up
+        chunks_free.erase(size_ptr_it->second);
+    } else {
+        // still some memory left in the chunk
+        auto it_remaining = size_to_free_chunk.emplace(size_remaining, size_ptr_it->second);
+        chunks_free[size_ptr_it->second] = it_remaining;
+        chunks_free_end.emplace(size_ptr_it->second + size_remaining, it_remaining);
+    }
+    size_to_free_chunk.erase(size_ptr_it);
+
+    return reinterpret_cast<void*>(allocated->first);
+}
+
+void Arena::free(void *ptr)
+{
+    // Freeing the nullptr pointer is OK.
+    if (ptr == nullptr) {
+        return;
+    }
+
+    // Remove chunk from used map
+    auto i = chunks_used.find(static_cast<char*>(ptr));
+    if (i == chunks_used.end()) {
+        throw std::runtime_error("Arena: invalid or double free");
+    }
+    std::pair<char*, size_t> freed = *i;
+    chunks_used.erase(i);
+
+    // coalesce freed with previous chunk
+    auto prev = chunks_free_end.find(freed.first);
+    if (prev != chunks_free_end.end()) {
+        freed.first -= prev->second->first;
+        freed.second += prev->second->first;
+        size_to_free_chunk.erase(prev->second);
+        chunks_free_end.erase(prev);
+    }
+
+    // coalesce freed with chunk after freed
+    auto next = chunks_free.find(freed.first + freed.second);
+    if (next != chunks_free.end()) {
+        freed.second += next->second->first;
+        size_to_free_chunk.erase(next->second);
+        chunks_free.erase(next);
+    }
+
+    // Add/set space with coalesced free chunk
+    auto it = size_to_free_chunk.emplace(freed.second, freed.first);
+    chunks_free[freed.first] = it;
+    chunks_free_end[freed.first + freed.second] = it;
+}
+
+Arena::Stats Arena::stats() const
+{
+    Arena::Stats r{ 0, 0, 0, chunks_used.size(), chunks_free.size() };
+    for (const auto& chunk: chunks_used)
+        r.used += chunk.second;
+    for (const auto& chunk: chunks_free)
+        r.free += chunk.second->first;
+    r.total = r.used + r.free;
+    return r;
+}
+
+#ifdef ARENA_DEBUG
+static void printchunk(void* base, size_t sz, bool used) {
+    std::cout <<
+        "0x" << std::hex << std::setw(16) << std::setfill('0') << base <<
+        " 0x" << std::hex << std::setw(16) << std::setfill('0') << sz <<
+        " 0x" << used << std::endl;
+}
+void Arena::walk() const
+{
+    for (const auto& chunk: chunks_used)
+        printchunk(chunk.first, chunk.second, true);
+    std::cout << std::endl;
+    for (const auto& chunk: chunks_free)
+        printchunk(chunk.first, chunk.second->first, false);
+    std::cout << std::endl;
+}
+#endif
+
+/*******************************************************************************/
+// Implementation: Win32LockedPageAllocator
+
+#ifdef WIN32
+/** LockedPageAllocator specialized for Windows.
+ */
+class Win32LockedPageAllocator: public LockedPageAllocator
+{
+public:
+    Win32LockedPageAllocator();
+    void* AllocateLocked(size_t len, bool *lockingSuccess) override;
+    void FreeLocked(void* addr, size_t len) override;
+    size_t GetLimit() override;
+private:
+    size_t page_size;
+};
+
+Win32LockedPageAllocator::Win32LockedPageAllocator()
+{
+    // Determine system page size in bytes
+    SYSTEM_INFO sSysInfo;
+    GetSystemInfo(&sSysInfo);
+    page_size = sSysInfo.dwPageSize;
+}
+void *Win32LockedPageAllocator::AllocateLocked(size_t len, bool *lockingSuccess)
+{
+    len = align_up(len, page_size);
+    void *addr = VirtualAlloc(nullptr, len, MEM_COMMIT | MEM_RESERVE, PAGE_READWRITE);
+    if (addr) {
+        // VirtualLock is used to attempt to keep keying material out of swap. Note
+        // that it does not provide this as a guarantee, but, in practice, memory
+        // that has been VirtualLock'd almost never gets written to the pagefile
+        // except in rare circumstances where memory is extremely low.
+        *lockingSuccess = VirtualLock(const_cast<void*>(addr), len) != 0;
+    }
+    return addr;
+}
+void Win32LockedPageAllocator::FreeLocked(void* addr, size_t len)
+{
+    len = align_up(len, page_size);
+    memory_cleanse(addr, len);
+    VirtualUnlock(const_cast<void*>(addr), len);
+}
+
+size_t Win32LockedPageAllocator::GetLimit()
+{
+    // TODO is there a limit on Windows, how to get it?
+    return std::numeric_limits<size_t>::max();
+}
+#endif
+
+/*******************************************************************************/
+// Implementation: PosixLockedPageAllocator
+
+#ifndef WIN32
+/** LockedPageAllocator specialized for OSes that don't try to be
+ * special snowflakes.
+ */
+class PosixLockedPageAllocator: public LockedPageAllocator
+{
+public:
+    PosixLockedPageAllocator();
+    void* AllocateLocked(size_t len, bool *lockingSuccess) override;
+    void FreeLocked(void* addr, size_t len) override;
+    size_t GetLimit() override;
+private:
+    size_t page_size;
+};
+
+PosixLockedPageAllocator::PosixLockedPageAllocator()
+{
+    // Determine system page size in bytes
+#if defined(PAGESIZE) // defined in limits.h
+    page_size = PAGESIZE;
+#else                   // assume some POSIX OS
+    page_size = sysconf(_SC_PAGESIZE);
+#endif
+}
+
+// Some systems (at least OS X) do not define MAP_ANONYMOUS yet and define
+// MAP_ANON which is deprecated
+#ifndef MAP_ANONYMOUS
+#define MAP_ANONYMOUS MAP_ANON
+#endif
+
+void *PosixLockedPageAllocator::AllocateLocked(size_t len, bool *lockingSuccess)
+{
+    void *addr;
+    len = align_up(len, page_size);
+    addr = mmap(nullptr, len, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
+    if (addr == MAP_FAILED) {
+        return nullptr;
+    }
+    if (addr) {
+        *lockingSuccess = mlock(addr, len) == 0;
+#if defined(MADV_DONTDUMP) // Linux
+        madvise(addr, len, MADV_DONTDUMP);
+#elif defined(MADV_NOCORE) // FreeBSD
+        madvise(addr, len, MADV_NOCORE);
+#endif
+    }
+    return addr;
+}
+void PosixLockedPageAllocator::FreeLocked(void* addr, size_t len)
+{
+    len = align_up(len, page_size);
+    memory_cleanse(addr, len);
+    munlock(addr, len);
+    munmap(addr, len);
+}
+size_t PosixLockedPageAllocator::GetLimit()
+{
+#ifdef RLIMIT_MEMLOCK
+    struct rlimit rlim;
+    if (getrlimit(RLIMIT_MEMLOCK, &rlim) == 0) {
+        if (rlim.rlim_cur != RLIM_INFINITY) {
+            return rlim.rlim_cur;
+        }
+    }
+#endif
+    return std::numeric_limits<size_t>::max();
+}
+#endif
+
+/*******************************************************************************/
+// Implementation: LockedPool
+
+LockedPool::LockedPool(std::unique_ptr<LockedPageAllocator> allocator_in, LockingFailed_Callback lf_cb_in):
+    allocator(std::move(allocator_in)), lf_cb(lf_cb_in), cumulative_bytes_locked(0)
+{
+}
+
+LockedPool::~LockedPool()
+{
+}
+void* LockedPool::alloc(size_t size)
+{
+    std::lock_guard<std::mutex> lock(mutex);
+
+    // Don't handle impossible sizes
+    if (size == 0 || size > ARENA_SIZE)
+        return nullptr;
+
+    // Try allocating from each current arena
+    for (auto &arena: arenas) {
+        void *addr = arena.alloc(size);
+        if (addr) {
+            return addr;
+        }
+    }
+    // If that fails, create a new one
+    if (new_arena(ARENA_SIZE, ARENA_ALIGN)) {
+        return arenas.back().alloc(size);
+    }
+    return nullptr;
+}
+
+void LockedPool::free(void *ptr)
+{
+    std::lock_guard<std::mutex> lock(mutex);
+    // TODO we can do better than this linear search by keeping a map of arena
+    // extents to arena, and looking up the address.
+    for (auto &arena: arenas) {
+        if (arena.addressInArena(ptr)) {
+            arena.free(ptr);
+            return;
+        }
+    }
+    throw std::runtime_error("LockedPool: invalid address not pointing to any arena");
+}
+
+LockedPool::Stats LockedPool::stats() const
+{
+    std::lock_guard<std::mutex> lock(mutex);
+    LockedPool::Stats r{0, 0, 0, cumulative_bytes_locked, 0, 0};
+    for (const auto &arena: arenas) {
+        Arena::Stats i = arena.stats();
+        r.used += i.used;
+        r.free += i.free;
+        r.total += i.total;
+        r.chunks_used += i.chunks_used;
+        r.chunks_free += i.chunks_free;
+    }
+    return r;
+}
+
+bool LockedPool::new_arena(size_t size, size_t align)
+{
+    bool locked;
+    // If this is the first arena, handle this specially: Cap the upper size
+    // by the process limit. This makes sure that the first arena will at least
+    // be locked. An exception to this is if the process limit is 0:
+    // in this case no memory can be locked at all so we'll skip past this logic.
+    if (arenas.empty()) {
+        size_t limit = allocator->GetLimit();
+        if (limit > 0) {
+            size = std::min(size, limit);
+        }
+    }
+    void *addr = allocator->AllocateLocked(size, &locked);
+    if (!addr) {
+        return false;
+    }
+    if (locked) {
+        cumulative_bytes_locked += size;
+    } else if (lf_cb) { // Call the locking-failed callback if locking failed
+        if (!lf_cb()) { // If the callback returns false, free the memory and fail, otherwise consider the user warned and proceed.
+            allocator->FreeLocked(addr, size);
+            return false;
+        }
+    }
+    arenas.emplace_back(allocator.get(), addr, size, align);
+    return true;
+}
+
+LockedPool::LockedPageArena::LockedPageArena(LockedPageAllocator *allocator_in, void *base_in, size_t size_in, size_t align_in):
+    Arena(base_in, size_in, align_in), base(base_in), size(size_in), allocator(allocator_in)
+{
+}
+LockedPool::LockedPageArena::~LockedPageArena()
+{
+    allocator->FreeLocked(base, size);
+}
+
+/*******************************************************************************/
+// Implementation: LockedPoolManager
+//
+LockedPoolManager::LockedPoolManager(std::unique_ptr<LockedPageAllocator> allocator_in):
+    LockedPool(std::move(allocator_in), &LockedPoolManager::LockingFailed)
+{
+}
+
+bool LockedPoolManager::LockingFailed()
+{
+    // TODO: log something but how? without including util.h
+    return true;
+}
+
+void LockedPoolManager::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
+    // LockedPoolManagerBase's destructor helps us detect if that ever happens.
+#ifdef WIN32
+    std::unique_ptr<LockedPageAllocator> allocator(new Win32LockedPageAllocator());
+#else
+    std::unique_ptr<LockedPageAllocator> allocator(new PosixLockedPageAllocator());
+#endif
+    static LockedPoolManager instance(std::move(allocator));
+    LockedPoolManager::_instance = &instance;
+}

src/support/lockedpool.h

@@ -0,0 +1,241 @@
+// Copyright (c) 2009-2020 The Bitcoin Core developers
+// Copyright (c) 2014-2020 The DigiByte Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef DIGIBYTE_SUPPORT_LOCKEDPOOL_H
+#define DIGIBYTE_SUPPORT_LOCKEDPOOL_H
+
+#include <stdint.h>
+#include <list>
+#include <map>
+#include <mutex>
+#include <memory>
+#include <unordered_map>
+
+/**
+ * OS-dependent allocation and deallocation of locked/pinned memory pages.
+ * Abstract base class.
+ */
+class LockedPageAllocator
+{
+public:
+    virtual ~LockedPageAllocator() {}
+    /** Allocate and lock memory pages.
+     * If len is not a multiple of the system page size, it is rounded up.
+     * Returns nullptr in case of allocation failure.
+     *
+     * If locking the memory pages could not be accomplished it will still
+     * return the memory, however the lockingSuccess flag will be false.
+     * lockingSuccess is undefined if the allocation fails.
+     */
+    virtual void* AllocateLocked(size_t len, bool *lockingSuccess) = 0;
+
+    /** Unlock and free memory pages.
+     * Clear the memory before unlocking.
+     */
+    virtual void FreeLocked(void* addr, size_t len) = 0;
+
+    /** Get the total limit on the amount of memory that may be locked by this
+     * process, in bytes. Return size_t max if there is no limit or the limit
+     * is unknown. Return 0 if no memory can be locked at all.
+     */
+    virtual size_t GetLimit() = 0;
+};
+
+/* An arena manages a contiguous region of memory by dividing it into
+ * chunks.
+ */
+class Arena
+{
+public:
+    Arena(void *base, size_t size, size_t alignment);
+    virtual ~Arena();
+
+    Arena(const Arena& other) = delete; // non construction-copyable
+    Arena& operator=(const Arena&) = delete; // non copyable
+
+    /** Memory statistics. */
+    struct Stats
+    {
+        size_t used;
+        size_t free;
+        size_t total;
+        size_t chunks_used;
+        size_t chunks_free;
+    };
+
+    /** Allocate size bytes from this arena.
+     * Returns pointer on success, or 0 if memory is full or
+     * the application tried to allocate 0 bytes.
+     */
+    void* alloc(size_t size);
+
+    /** Free a previously allocated chunk of memory.
+     * Freeing the zero pointer has no effect.
+     * Raises std::runtime_error in case of error.
+     */
+    void free(void *ptr);
+
+    /** Get arena usage statistics */
+    Stats stats() const;
+
+#ifdef ARENA_DEBUG
+    void walk() const;
+#endif
+
+    /** Return whether a pointer points inside this arena.
+     * This returns base <= ptr < (base+size) so only use it for (inclusive)
+     * chunk starting addresses.
+     */
+    bool addressInArena(void *ptr) const { return ptr >= base && ptr < end; }
+private:
+    typedef std::multimap<size_t, char*> SizeToChunkSortedMap;
+    /** Map to enable O(log(n)) best-fit allocation, as it's sorted by size */
+    SizeToChunkSortedMap size_to_free_chunk;
+
+    typedef std::unordered_map<char*, SizeToChunkSortedMap::const_iterator> ChunkToSizeMap;
+    /** Map from begin of free chunk to its node in size_to_free_chunk */
+    ChunkToSizeMap chunks_free;
+    /** Map from end of free chunk to its node in size_to_free_chunk */
+    ChunkToSizeMap chunks_free_end;
+
+    /** Map from begin of used chunk to its size */
+    std::unordered_map<char*, size_t> chunks_used;
+
+    /** Base address of arena */
+    char* base;
+    /** End address of arena */
+    char* end;
+    /** Minimum chunk alignment */
+    size_t alignment;
+};
+
+/** Pool for locked memory chunks.
+ *
+ * To avoid sensitive key data from being swapped to disk, the memory in this pool
+ * is locked/pinned.
+ *
+ * An arena manages a contiguous region of memory. The pool starts out with one arena
+ * but can grow to multiple arenas if the need arises.
+ *
+ * Unlike a normal C heap, the administrative structures are separate from the managed
+ * memory. This has been done as the sizes and bases of objects are not in themselves sensitive
+ * information, as to conserve precious locked memory. In some operating systems
+ * the amount of memory that can be locked is small.
+ */
+class LockedPool
+{
+public:
+    /** Size of one arena of locked memory. This is a compromise.
+     * Do not set this too low, as managing many arenas will increase
+     * allocation and deallocation overhead. Setting it too high allocates
+     * more locked memory from the OS than strictly necessary.
+     */
+    static const size_t ARENA_SIZE = 256*1024;
+    /** Chunk alignment. Another compromise. Setting this too high will waste
+     * memory, setting it too low will facilitate fragmentation.
+     */
+    static const size_t ARENA_ALIGN = 16;
+
+    /** Callback when allocation succeeds but locking fails.
+     */
+    typedef bool (*LockingFailed_Callback)();
+
+    /** Memory statistics. */
+    struct Stats
+    {
+        size_t used;
+        size_t free;
+        size_t total;
+        size_t locked;
+        size_t chunks_used;
+        size_t chunks_free;
+    };
+
+    /** Create a new LockedPool. This takes ownership of the MemoryPageLocker,
+     * you can only instantiate this with LockedPool(std::move(...)).
+     *
+     * The second argument is an optional callback when locking a newly allocated arena failed.
+     * If this callback is provided and returns false, the allocation fails (hard fail), if
+     * it returns true the allocation proceeds, but it could warn.
+     */
+    explicit LockedPool(std::unique_ptr<LockedPageAllocator> allocator, LockingFailed_Callback lf_cb_in = nullptr);
+    ~LockedPool();
+
+    LockedPool(const LockedPool& other) = delete; // non construction-copyable
+    LockedPool& operator=(const LockedPool&) = delete; // non copyable
+
+    /** Allocate size bytes from this arena.
+     * Returns pointer on success, or 0 if memory is full or
+     * the application tried to allocate 0 bytes.
+     */
+    void* alloc(size_t size);
+
+    /** Free a previously allocated chunk of memory.
+     * Freeing the zero pointer has no effect.
+     * Raises std::runtime_error in case of error.
+     */
+    void free(void *ptr);
+
+    /** Get pool usage statistics */
+    Stats stats() const;
+private:
+    std::unique_ptr<LockedPageAllocator> allocator;
+
+    /** Create an arena from locked pages */
+    class LockedPageArena: public Arena
+    {
+    public:
+        LockedPageArena(LockedPageAllocator *alloc_in, void *base_in, size_t size, size_t align);
+        ~LockedPageArena();
+    private:
+        void *base;
+        size_t size;
+        LockedPageAllocator *allocator;
+    };
+
+    bool new_arena(size_t size, size_t align);
+
+    std::list<LockedPageArena> arenas;
+    LockingFailed_Callback lf_cb;
+    size_t cumulative_bytes_locked;
+    /** Mutex protects access to this pool's data structures, including arenas.
+     */
+    mutable std::mutex mutex;
+};
+
+/**
+ * Singleton class to keep track of locked (ie, non-swappable) memory, 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
+ * LockedPoolManager instance exists before any other STL-based objects that use
+ * secure_allocator are created. So instead of having LockedPoolManager also be
+ * static-initialized, it is created on demand.
+ */
+class LockedPoolManager : public LockedPool
+{
+public:
+    /** Return the current instance, or create it once */
+    static LockedPoolManager& Instance()
+    {
+        static std::once_flag init_flag;
+        std::call_once(init_flag, LockedPoolManager::CreateInstance);
+        return *LockedPoolManager::_instance;
+    }
+
+private:
+    explicit LockedPoolManager(std::unique_ptr<LockedPageAllocator> allocator);
+
+    /** Create a new LockedPoolManager specialized to the OS */
+    static void CreateInstance();
+    /** Called when locking fails, warn the user here */
+    static bool LockingFailed();
+
+    static LockedPoolManager* _instance;
+};
+
+#endif // DIGIBYTE_SUPPORT_LOCKEDPOOL_H