Paul Crowley | 220567c | 2020-02-07 12:45:20 -0800 | [diff] [blame] | 1 | /* |
| 2 | * Copyright (C) 2020 The Android Open Source Project |
| 3 | * |
| 4 | * Licensed under the Apache License, Version 2.0 (the "License"); |
| 5 | * you may not use this file except in compliance with the License. |
| 6 | * You may obtain a copy of the License at |
| 7 | * |
| 8 | * http://www.apache.org/licenses/LICENSE-2.0 |
| 9 | * |
| 10 | * Unless required by applicable law or agreed to in writing, software |
| 11 | * distributed under the License is distributed on an "AS IS" BASIS, |
| 12 | * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| 13 | * See the License for the specific language governing permissions and |
| 14 | * limitations under the License. |
| 15 | */ |
| 16 | |
| 17 | #pragma once |
| 18 | |
| 19 | #include <stdlib.h> |
| 20 | |
| 21 | namespace android { |
| 22 | namespace vold { |
| 23 | |
| 24 | // Struct representing an encryption algorithm supported by vold. |
| 25 | // "config_name" represents the name we give the algorithm in |
| 26 | // read-only properties and fstab files |
| 27 | // "kernel_name" is the name we present to the Linux kernel |
| 28 | // "keysize" is the size of the key in bytes. |
| 29 | struct CryptoType { |
| 30 | // We should only be constructing CryptoTypes as part of |
| 31 | // supported_crypto_types[]. We do it via this pseudo-builder pattern, |
| 32 | // which isn't pure or fully protected as a concession to being able to |
| 33 | // do it all at compile time. Add new CryptoTypes in |
| 34 | // supported_crypto_types[] below. |
| 35 | constexpr CryptoType() : CryptoType(nullptr, nullptr, 0xFFFFFFFF) {} |
| 36 | constexpr CryptoType set_keysize(size_t size) const { |
| 37 | return CryptoType(this->config_name, this->kernel_name, size); |
| 38 | } |
| 39 | constexpr CryptoType set_config_name(const char* property) const { |
| 40 | return CryptoType(property, this->kernel_name, this->keysize); |
| 41 | } |
| 42 | constexpr CryptoType set_kernel_name(const char* crypto) const { |
| 43 | return CryptoType(this->config_name, crypto, this->keysize); |
| 44 | } |
| 45 | |
| 46 | constexpr const char* get_config_name() const { return config_name; } |
| 47 | constexpr const char* get_kernel_name() const { return kernel_name; } |
| 48 | constexpr size_t get_keysize() const { return keysize; } |
| 49 | |
| 50 | private: |
| 51 | const char* config_name; |
| 52 | const char* kernel_name; |
| 53 | size_t keysize; |
| 54 | |
| 55 | constexpr CryptoType(const char* property, const char* crypto, size_t ksize) |
| 56 | : config_name(property), kernel_name(crypto), keysize(ksize) {} |
| 57 | }; |
| 58 | |
| 59 | // Use the named android property to look up a type from the table |
| 60 | // If the property is not set or matches no table entry, return the default. |
| 61 | const CryptoType& lookup_crypto_algorithm(const CryptoType table[], int table_len, |
| 62 | const CryptoType& default_alg, const char* property); |
| 63 | |
| 64 | // Some useful types |
| 65 | |
| 66 | constexpr CryptoType invalid_crypto_type = CryptoType(); |
| 67 | |
| 68 | constexpr CryptoType aes_256_xts = CryptoType() |
| 69 | .set_config_name("aes-256-xts") |
| 70 | .set_kernel_name("aes-xts-plain64") |
| 71 | .set_keysize(64); |
| 72 | |
| 73 | constexpr CryptoType adiantum = CryptoType() |
| 74 | .set_config_name("adiantum") |
| 75 | .set_kernel_name("xchacha12,aes-adiantum-plain64") |
| 76 | .set_keysize(32); |
| 77 | |
| 78 | // Support compile-time validation of a crypto type table |
| 79 | |
| 80 | template <typename T, size_t N> |
| 81 | constexpr size_t array_length(T (&)[N]) { |
| 82 | return N; |
| 83 | } |
| 84 | |
| 85 | constexpr bool isValidCryptoType(size_t max_keylen, const CryptoType& crypto_type) { |
| 86 | return ((crypto_type.get_config_name() != nullptr) && |
| 87 | (crypto_type.get_kernel_name() != nullptr) && |
| 88 | (crypto_type.get_keysize() <= max_keylen)); |
| 89 | } |
| 90 | |
| 91 | // Confirms that all supported_crypto_types have a small enough keysize and |
| 92 | // had both set_config_name() and set_kernel_name() called. |
| 93 | // Note in C++11 that constexpr functions can only have a single line. |
| 94 | // So our code is a bit convoluted (using recursion instead of a loop), |
| 95 | // but it's asserting at compile time that all of our key lengths are valid. |
| 96 | constexpr bool validateSupportedCryptoTypes(size_t max_keylen, const CryptoType types[], |
| 97 | size_t len) { |
| 98 | return len == 0 || (isValidCryptoType(max_keylen, types[len - 1]) && |
| 99 | validateSupportedCryptoTypes(max_keylen, types, len - 1)); |
| 100 | } |
| 101 | |
| 102 | } // namespace vold |
| 103 | } // namespace android |