Allocating and cleansing sensitive Bitcoin memory

1// Copyright (c) 2009-2010 Satoshi Nakamoto
2// Copyright (c) 2009-present The Bitcoin Core developers
3// Distributed under the MIT software license, see the accompanying
4// file COPYING or http://www.opensource.org/licenses/mit-license.php.
5
6#ifndef BITCOIN_SUPPORT_ALLOCATORS_SECURE_H
7#define BITCOIN_SUPPORT_ALLOCATORS_SECURE_H
8
9#include <support/lockedpool.h>
10#include <support/cleanse.h>
11
12#include <memory>
13#include <string>
14
15//
16// Allocator that locks its contents from being paged
17// out of memory and clears its contents before deletion.
18//
19template <typename T>
20struct secure_allocator {
21    using value_type = T;
22
23    secure_allocator() = default;
24    template <typename U>
25    secure_allocator(const secure_allocator<U>&) noexcept {}
26
27    T* allocate(std::size_t n)
28    {
29        T* allocation = static_cast<T*>(LockedPoolManager::Instance().alloc(sizeof(T) * n));
30        if (!allocation) {
31            throw std::bad_alloc();
32        }
33        return allocation;
34    }
35
36    void deallocate(T* p, std::size_t n)
37    {
38        if (p != nullptr) {
39            memory_cleanse(p, sizeof(T) * n);
40        }
41        LockedPoolManager::Instance().free(p);
42    }
43
44    template <typename U>
45    friend bool operator==(const secure_allocator&, const secure_allocator<U>&) noexcept
46    {
47        return true;
48    }
49};
50
51// This is exactly like std::string, but with a custom allocator.
52// TODO: Consider finding a way to make incoming RPC request.params[i] mlock()ed as well
53typedef std::basic_string<char, std::char_traits<char>, secure_allocator<char> > SecureString;
54
55template<typename T>
56struct SecureUniqueDeleter {
57    void operator()(T* t) noexcept {
58        secure_allocator<T>().deallocate(t, 1);
59    }
60};
61
62template<typename T>
63using secure_unique_ptr = std::unique_ptr<T, SecureUniqueDeleter<T>>;
64
65template<typename T, typename... Args>
66secure_unique_ptr<T> make_secure_unique(Args&&... as)
67{
68    T* p = secure_allocator<T>().allocate(1);
69
70    // initialize in place, and return as secure_unique_ptr
71    try {
72        return secure_unique_ptr<T>(new (p) T(std::forward<Args>(as)...));
73    } catch (...) {
74        secure_allocator<T>().deallocate(p, 1);
75        throw;
76    }
77}
78
79#endif // BITCOIN_SUPPORT_ALLOCATORS_SECURE_H
80