include/keymaster/mem.h

/*
 * Copyright 2021 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#pragma once

namespace keymaster {

/*
 * Array Manipulation functions.  This set of templated inline functions provides some nice tools
 * for operating on c-style arrays.  C-style arrays actually do have a defined size associated with
 * them, as long as they are not allowed to decay to a pointer.  These template methods exploit this
 * to allow size-based array operations without explicitly specifying the size.  If passed a pointer
 * rather than an array, they'll fail to compile.
 */

/**
 * Return the size in bytes of the array \p a.
 */
template <typename T, size_t N> inline size_t array_size(const T (&a)[N]) {
    return sizeof(a);
}

/**
 * Return the number of elements in array \p a.
 */
template <typename T, size_t N> inline size_t array_length(const T (&)[N]) {
    return N;
}

/**
 * Duplicate the array \p a.  The memory for the new array is allocated and the caller takes
 * responsibility.
 */
template <typename T> inline T* dup_array(const T* a, size_t n) {
    T* dup = new (std::nothrow) T[n];
    if (dup)
        for (size_t i = 0; i < n; ++i)
            dup[i] = a[i];
    return dup;
}

/**
 * Duplicate the array \p a.  The memory for the new array is allocated and the caller takes
 * responsibility.  Note that the dup is necessarily returned as a pointer, so size is lost.  Call
 * array_length() on the original array to discover the size.
 */
template <typename T, size_t N> inline T* dup_array(const T (&a)[N]) {
    return dup_array(a, N);
}

/**
 * Duplicate the buffer \p buf.  The memory for the new buffer is allocated and the caller takes
 * responsibility.
 */
uint8_t* dup_buffer(const void* buf, size_t size);

/**
 * Copy the contents of array \p arr to \p dest.
 */
template <typename T, size_t N> inline void copy_array(const T (&arr)[N], T* dest) {
    for (size_t i = 0; i < N; ++i)
        dest[i] = arr[i];
}

/**
 * Search array \p a for value \p val, returning true if found.  Note that this function is
 * early-exit, meaning that it should not be used in contexts where timing analysis attacks could be
 * a concern.
 */
template <typename T, size_t N> inline bool array_contains(const T (&a)[N], T val) {
    for (size_t i = 0; i < N; ++i) {
        if (a[i] == val) {
            return true;
        }
    }
    return false;
}

/**
 * Variant of memset() that uses GCC-specific pragmas to disable optimizations, so effect is not
 * optimized away.  This is important because we often need to wipe blocks of sensitive data from
 * memory.  As an additional convenience, this implementation avoids writing to NULL pointers.
 */
#ifdef __clang__
#define OPTNONE __attribute__((optnone))
#else  // not __clang__
#define OPTNONE __attribute__((optimize("O0")))
#endif  // not __clang__
inline OPTNONE void* memset_s(void* s, int c, size_t n) {
    if (!s) return s;
    return memset(s, c, n);
}
#undef OPTNONE

/**
 * Variant of memcmp that has the same runtime regardless of whether the data matches (i.e. doesn't
 * short-circuit).  Not an exact equivalent to memcmp because it doesn't return <0 if p1 < p2, just
 * 0 for match and non-zero for non-match.
 */
int memcmp_s(const void* p1, const void* p2, size_t length);

/**
 * Eraser clears buffers.  Construct it with a buffer or object and the destructor will ensure that
 * it is zeroed.
 */
class Eraser {
  public:
    /* Not implemented.  If this gets used, we want a link error. */
    template <typename T> explicit Eraser(T* t);

    template <typename T>
    explicit Eraser(T& t) : buf_(reinterpret_cast<uint8_t*>(&t)), size_(sizeof(t)) {}

    template <size_t N> explicit Eraser(uint8_t (&arr)[N]) : buf_(arr), size_(N) {}

    Eraser(void* buf, size_t size) : buf_(static_cast<uint8_t*>(buf)), size_(size) {}
    ~Eraser() { memset_s(buf_, 0, size_); }

  private:
    Eraser(const Eraser&);
    void operator=(const Eraser&);

    uint8_t* buf_;
    size_t size_;
};

/**
 * ArrayWrapper is a trivial wrapper around a C-style array that provides begin() and end()
 * methods. This is primarily to facilitate range-based iteration on arrays.  It does not copy, nor
 * does it take ownership; it just holds pointers.
 */
template <typename T> class ArrayWrapper {
  public:
    ArrayWrapper(T* array, size_t size) : begin_(array), end_(array + size) {}

    T* begin() { return begin_; }
    T* end() { return end_; }

  private:
    T* begin_;
    T* end_;
};

template <typename T> ArrayWrapper<T> array_range(T* begin, size_t length) {
    return ArrayWrapper<T>(begin, length);
}

template <typename T, size_t n> ArrayWrapper<T> array_range(T (&a)[n]) {
    return ArrayWrapper<T>(a, n);
}

struct Malloc_Delete {
    void operator()(void* p) { free(p); }
};

}  // namespace keymaster