| Will Harris | f6cca058 | 2024-10-11 23:53:50 | [diff] [blame] | 1 | // Copyright 2024 The Chromium Authors |
| 2 | // Use of this source code is governed by a BSD-style license that can be |
| 3 | // found in the LICENSE file. |
| 4 | |
| 5 | #ifndef CRYPTO_PROCESS_BOUND_STRING_H_ |
| 6 | #define CRYPTO_PROCESS_BOUND_STRING_H_ |
| 7 | |
| 8 | #include<string> |
| 9 | #include<vector> |
| 10 | |
| 11 | #include"base/check.h" |
| 12 | #include"base/containers/span.h" |
| 13 | #include"base/feature_list.h" |
| 14 | #include"base/gtest_prod_util.h" |
| 15 | #include"crypto/crypto_export.h" |
| 16 | #include"crypto/features.h" |
| 17 | |
| 18 | namespace crypto{ |
| 19 | |
| 20 | namespaceinternal{ |
| 21 | |
| 22 | // Maybe round the size of the data to a size needed for the encrypt or decrypt |
| 23 | // operation. Returns the new size, or `size` if no rounding up is needed. |
| 24 | CRYPTO_EXPORTsize_tMaybeRoundUp(size_t size); |
| 25 | |
| 26 | // Maybe encrypt a buffer, in place. Returns true if the buffer was successfully |
| 27 | // encrypted or false if unsupported by the platform or failed to encrypt. |
| 28 | CRYPTO_EXPORTboolMaybeEncryptBuffer(base::span<uint8_t> buffer); |
| 29 | |
| 30 | // Maybe decrypt a buffer, in place. Returns true if the buffer was successfully |
| 31 | // decrypted or false if unsupported by the platform or failed to decrypt. |
| 32 | CRYPTO_EXPORTboolMaybeDecryptBuffer(base::span<uint8_t> buffer); |
| 33 | |
| 34 | // Securely zero a buffer using a platform specific method. |
| 35 | CRYPTO_EXPORTvoidSecureZeroBuffer(base::span<uint8_t> buffer); |
| 36 | |
| 37 | }// namespace internal |
| 38 | |
| 39 | // SecureAllocator is used by the SecureString variants below to clear the |
| 40 | // memory when the string moves out of scope. |
| 41 | template<typename T> |
| 42 | struct CRYPTO_EXPORTSecureAllocator{ |
| 43 | using value_type= T; |
| 44 | |
| 45 | SecureAllocator() noexcept=default; |
| 46 | |
| 47 | T* allocate(std::size_t n){return std::allocator<T>().allocate(n);} |
| 48 | |
| 49 | void deallocate(T* p, std::size_t n) noexcept{ |
| 50 | if(p){ |
| 51 | // SAFETY: deallocate() has a fixed prototype from the std library, and |
| 52 | // passes an unsafe buffer, so convert it to a base::span here. |
| 53 | internal::SecureZeroBuffer(UNSAFE_BUFFERS( |
| 54 | base::span<uint8_t>(reinterpret_cast<uint8_t*>(p), n*sizeof(T)))); |
| 55 | std::allocator<T>().deallocate(p, n); |
| 56 | } |
| 57 | } |
| 58 | }; |
| 59 | |
| 60 | // On supported platforms, a process bound string cannot have its content read |
| 61 | // by other processes on the system. On unsupported platforms it provides no |
| 62 | // difference over a native string except it does more copies. |
| 63 | template<typenameStringType> |
| 64 | class CRYPTO_EXPORTProcessBound{ |
| 65 | public: |
| 66 | usingCharType=typenameStringType::value_type; |
| 67 | |
| 68 | ProcessBound(constProcessBound& other)=default; |
| 69 | ProcessBound(ProcessBound&& other)=default; |
| 70 | ProcessBound&operator=(constProcessBound& other)=default; |
| 71 | ProcessBound&operator=(ProcessBound&& other)=default; |
| 72 | |
| 73 | // Create a process bound string. Takes a copy of the string passed in. |
| 74 | explicitProcessBound(constStringType& value) |
| 75 | : original_size_(value.size()){ |
| 76 | std::vector<CharType> data(value.begin(), value.end()); |
| 77 | if(base::FeatureList::IsEnabled( |
| 78 | crypto::features::kProcessBoundStringEncryption)){ |
| 79 | data.resize(internal::MaybeRoundUp(data.size())); |
| 80 | encrypted_= |
| 81 | internal::MaybeEncryptBuffer(base::as_writable_byte_span(data)); |
| 82 | } |
| 83 | maybe_encrypted_data_= std::move(data); |
| 84 | } |
| 85 | |
| 86 | ~ProcessBound()=default; |
| 87 | |
| 88 | // Return the decrypted string. |
| 89 | StringType value()const{returnStringType(secure_value());} |
| 90 | |
| 91 | // Return the decrypted string as a string that attempts to wipe itself after |
| 92 | // use. Prefer over calling `value()` if caller can support it. |
| 93 | std::basic_string<CharType, |
| 94 | std::char_traits<CharType>, |
| 95 | SecureAllocator<CharType>> |
| 96 | secure_value()const{ |
| 97 | if(!encrypted_){ |
| 98 | return std::basic_string<CharType, std::char_traits<CharType>, |
| 99 | SecureAllocator<CharType>>( |
| 100 | maybe_encrypted_data_.data(), original_size_); |
| 101 | } |
| 102 | |
| 103 | // Copy to decrypt in-place. |
| 104 | std::basic_string<CharType, std::char_traits<CharType>, |
| 105 | SecureAllocator<CharType>> |
| 106 | decrypted(maybe_encrypted_data_.begin(), maybe_encrypted_data_.end()); |
| 107 | // Attempt to avoid Small String Optimization (SSO) by reserving a larger |
| 108 | // allocation than the SSO default, forcing a dynamic allocation to occur, |
| 109 | // before any decrypted data is written to the string. This value was |
| 110 | // determined empirically. |
| 111 | constexprsize_t kSSOMaxSize=64u; |
| 112 | if(decrypted.size()< kSSOMaxSize){ |
| 113 | decrypted.reserve(kSSOMaxSize); |
| 114 | } |
| 115 | CHECK(internal::MaybeDecryptBuffer(base::as_writable_byte_span(decrypted))); |
| 116 | decrypted.resize(original_size_); |
| 117 | return decrypted; |
| 118 | } |
| 119 | |
| 120 | size_t size()const{return original_size_;} |
| 121 | bool empty()const{return size()==0;} |
| 122 | |
| 123 | private: |
| 124 | FRIEND_TEST_ALL_PREFIXES(ProcessBoundFeatureTest,Encryption); |
| 125 | std::vector<CharType> maybe_encrypted_data_; |
| 126 | size_t original_size_; |
| 127 | bool encrypted_=false; |
| 128 | }; |
| 129 | |
| 130 | usingProcessBoundString=ProcessBound<std::string>; |
| 131 | usingProcessBoundWString=ProcessBound<std::wstring>; |
| 132 | usingProcessBoundU16String=ProcessBound<std::u16string>; |
| 133 | |
| 134 | // SecureString variants here attempt to clean memory for the string data when |
| 135 | // the string goes out of scope. However, while in memory it can be read, and if |
| 136 | // copied somewhere else, the memory can also be read. This is a defense in |
| 137 | // depth hardening and not meant to provide strong security guarantees. |
| 138 | usingSecureString= |
| 139 | std::basic_string<std::string::value_type, |
| 140 | std::char_traits<std::string::value_type>, |
| 141 | SecureAllocator<std::string::value_type>>; |
| 142 | usingSecureWString= |
| 143 | std::basic_string<std::wstring::value_type, |
| 144 | std::char_traits<std::wstring::value_type>, |
| 145 | SecureAllocator<std::wstring::value_type>>; |
| 146 | usingSecureU16String= |
| 147 | std::basic_string<std::u16string::value_type, |
| 148 | std::char_traits<std::u16string::value_type>, |
| 149 | SecureAllocator<std::u16string::value_type>>; |
| 150 | |
| 151 | }// namespace crypto |
| 152 | |
| 153 | #endif// CRYPTO_PROCESS_BOUND_STRING_H_ |
