mem_ops.h

Go to the documentation of this file.

/*
* Memory Operations
* (C) 1999-2009,2012,2015 Jack Lloyd
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
 
#ifndef BOTAN_MEMORY_OPS_H_
#define BOTAN_MEMORY_OPS_H_
 
#include <botan/types.h>
#include <cstring>
#include <type_traits>
#include <vector>
 
namespace Botan {
 
/**
* Allocate a memory buffer by some method. This should only be used for
* primitive types (uint8_t, uint32_t, etc).
*
* @param elems the number of elements
* @param elem_size the size of each element
* @return pointer to allocated and zeroed memory, or throw std::bad_alloc on failure
*/
BOTAN_PUBLIC_API(2,3) BOTAN_MALLOC_FN void* allocate_memory(size_t elems, size_t elem_size);
 
/**
* Free a pointer returned by allocate_memory
* @param p the pointer returned by allocate_memory
* @param elems the number of elements, as passed to allocate_memory
* @param elem_size the size of each element, as passed to allocate_memory
*/
BOTAN_PUBLIC_API(2,3) void deallocate_memory(void* p, size_t elems, size_t elem_size);
 
/**
* Ensure the allocator is initialized
*/
void BOTAN_UNSTABLE_API initialize_allocator();
 
class Allocator_Initializer
   {
   public:
      Allocator_Initializer() { initialize_allocator(); }
   };
 
/**
* Scrub memory contents in a way that a compiler should not elide,
* using some system specific technique. Note that this function might
* not zero the memory (for example, in some hypothetical
* implementation it might combine the memory contents with the output
* of a system PRNG), but if you can detect any difference in behavior
* at runtime then the clearing is side-effecting and you can just
* use `clear_mem`.
*
* Use this function to scrub memory just before deallocating it, or on
* a stack buffer before returning from the function.
*
* @param ptr a pointer to memory to scrub
* @param n the number of bytes pointed to by ptr
*/
BOTAN_PUBLIC_API(2,0) void secure_scrub_memory(void* ptr, size_t n);
 
/**
* Memory comparison, input insensitive
* @param x a pointer to an array
* @param y a pointer to another array
* @param len the number of Ts in x and y
* @return 0xFF iff x[i] == y[i] forall i in [0...n) or 0x00 otherwise
*/
BOTAN_PUBLIC_API(2,9) uint8_t ct_compare_u8(const uint8_t x[],
                                            const uint8_t y[],
                                            size_t len);
 
/**
* Memory comparison, input insensitive
* @param x a pointer to an array
* @param y a pointer to another array
* @param len the number of Ts in x and y
* @return true iff x[i] == y[i] forall i in [0...n)
*/
inline bool constant_time_compare(const uint8_t x[],
                                  const uint8_t y[],
                                  size_t len)
   {
   return ct_compare_u8(x, y, len) == 0xFF;
   }
 
/**
* Zero out some bytes. Warning: use secure_scrub_memory instead if the
* memory is about to be freed or otherwise the compiler thinks it can
* elide the writes.
*
* @param ptr a pointer to memory to zero
* @param bytes the number of bytes to zero in ptr
*/
inline constexpr void clear_bytes(void* ptr, size_t bytes)
   {
   if(bytes > 0)
      {
      std::memset(ptr, 0, bytes);
      }
   }
 
/**
* Zero memory before use. This simply calls memset and should not be
* used in cases where the compiler cannot see the call as a
* side-effecting operation (for example, if calling clear_mem before
* deallocating memory, the compiler would be allowed to omit the call
* to memset entirely under the as-if rule.)
*
* @param ptr a pointer to an array of Ts to zero
* @param n the number of Ts pointed to by ptr
*/
template<typename T> inline constexpr void clear_mem(T* ptr, size_t n)
   {
   clear_bytes(ptr, sizeof(T)*n);
   }
 
/**
* Copy memory
* @param out the destination array
* @param in the source array
* @param n the number of elements of in/out
*/
template<typename T> inline constexpr void copy_mem(T* out, const T* in, size_t n)
   {
   static_assert(std::is_trivial<typename std::decay<T>::type>::value, "");
   BOTAN_ASSERT_IMPLICATION(n > 0, in != nullptr && out != nullptr,
                            "If n > 0 then args are not null");
 
   if(in != nullptr && out != nullptr && n > 0)
      {
      std::memmove(out, in, sizeof(T)*n);
      }
   }
 
template<typename T> inline constexpr void typecast_copy(uint8_t out[], T in[], size_t N)
   {
   static_assert(std::is_trivially_copyable<T>::value, "Safe to memcpy");
   std::memcpy(out, in, sizeof(T)*N);
   }
 
template<typename T> inline constexpr void typecast_copy(T out[], const uint8_t in[], size_t N)
   {
   static_assert(std::is_trivial<T>::value, "Safe to memcpy");
   std::memcpy(out, in, sizeof(T)*N);
   }
 
template<typename T> inline constexpr void typecast_copy(uint8_t out[], T in)
   {
   typecast_copy(out, &in, 1);
   }
 
template<typename T> inline constexpr void typecast_copy(T& out, const uint8_t in[])
   {
   static_assert(std::is_trivial<typename std::decay<T>::type>::value, "Safe case");
   typecast_copy(&out, in, 1);
   }
 
template <class To, class From> inline constexpr To typecast_copy(const From *src) noexcept
   {
   static_assert(std::is_trivially_copyable<From>::value && std::is_trivial<To>::value, "Safe for memcpy");
   To dst;
   std::memcpy(&dst, src, sizeof(To));
   return dst;
   }
 
/**
* Set memory to a fixed value
* @param ptr a pointer to an array of bytes
* @param n the number of Ts pointed to by ptr
* @param val the value to set each byte to
*/
inline constexpr void set_mem(uint8_t* ptr, size_t n, uint8_t val)
   {
   if(n > 0)
      {
      std::memset(ptr, val, n);
      }
   }
 
inline const uint8_t* cast_char_ptr_to_uint8(const char* s)
   {
   return reinterpret_cast<const uint8_t*>(s);
   }
 
inline const char* cast_uint8_ptr_to_char(const uint8_t* b)
   {
   return reinterpret_cast<const char*>(b);
   }
 
inline uint8_t* cast_char_ptr_to_uint8(char* s)
   {
   return reinterpret_cast<uint8_t*>(s);
   }
 
inline char* cast_uint8_ptr_to_char(uint8_t* b)
   {
   return reinterpret_cast<char*>(b);
   }
 
/**
* Memory comparison, input insensitive
* @param p1 a pointer to an array
* @param p2 a pointer to another array
* @param n the number of Ts in p1 and p2
* @return true iff p1[i] == p2[i] forall i in [0...n)
*/
template<typename T> inline bool same_mem(const T* p1, const T* p2, size_t n)
   {
   volatile T difference = 0;
 
   for(size_t i = 0; i != n; ++i)
      difference = difference | (p1[i] ^ p2[i]);
 
   return difference == 0;
   }
 
template<typename T, typename Alloc>
size_t buffer_insert(std::vector<T, Alloc>& buf,
                     size_t buf_offset,
                     const T input[],
                     size_t input_length)
   {
   BOTAN_ASSERT_NOMSG(buf_offset <= buf.size());
   const size_t to_copy = std::min(input_length, buf.size() - buf_offset);
   if(to_copy > 0)
      {
      copy_mem(&buf[buf_offset], input, to_copy);
      }
   return to_copy;
   }
 
template<typename T, typename Alloc, typename Alloc2>
size_t buffer_insert(std::vector<T, Alloc>& buf,
                     size_t buf_offset,
                     const std::vector<T, Alloc2>& input)
   {
   BOTAN_ASSERT_NOMSG(buf_offset <= buf.size());
   const size_t to_copy = std::min(input.size(), buf.size() - buf_offset);
   if(to_copy > 0)
      {
      copy_mem(&buf[buf_offset], input.data(), to_copy);
      }
   return to_copy;
   }
 
/**
* XOR arrays. Postcondition out[i] = in[i] ^ out[i] forall i = 0...length
* @param out the input/output buffer
* @param in the read-only input buffer
* @param length the length of the buffers
*/
inline void xor_buf(uint8_t out[],
                    const uint8_t in[],
                    size_t length)
   {
   const size_t blocks = length - (length % 32);
 
   for(size_t i = 0; i != blocks; i += 32)
      {
      uint64_t x[4];
      uint64_t y[4];
 
      typecast_copy(x, out + i, 4);
      typecast_copy(y, in + i, 4);
 
      x[0] ^= y[0];
      x[1] ^= y[1];
      x[2] ^= y[2];
      x[3] ^= y[3];
 
      typecast_copy(out + i, x, 4);
      }
 
   for(size_t i = blocks; i != length; ++i)
      {
      out[i] ^= in[i];
      }
   }
 
/**
* XOR arrays. Postcondition out[i] = in[i] ^ in2[i] forall i = 0...length
* @param out the output buffer
* @param in the first input buffer
* @param in2 the second output buffer
* @param length the length of the three buffers
*/
inline void xor_buf(uint8_t out[],
                    const uint8_t in[],
                    const uint8_t in2[],
                    size_t length)
   {
   const size_t blocks = length - (length % 32);
 
   for(size_t i = 0; i != blocks; i += 32)
      {
      uint64_t x[4];
      uint64_t y[4];
 
      typecast_copy(x, in + i, 4);
      typecast_copy(y, in2 + i, 4);
 
      x[0] ^= y[0];
      x[1] ^= y[1];
      x[2] ^= y[2];
      x[3] ^= y[3];
 
      typecast_copy(out + i, x, 4);
      }
 
   for(size_t i = blocks; i != length; ++i)
      {
      out[i] = in[i] ^ in2[i];
      }
   }
 
template<typename Alloc, typename Alloc2>
void xor_buf(std::vector<uint8_t, Alloc>& out,
             const std::vector<uint8_t, Alloc2>& in,
             size_t n)
   {
   xor_buf(out.data(), in.data(), n);
   }
 
template<typename Alloc>
void xor_buf(std::vector<uint8_t, Alloc>& out,
             const uint8_t* in,
             size_t n)
   {
   xor_buf(out.data(), in, n);
   }
 
template<typename Alloc, typename Alloc2>
void xor_buf(std::vector<uint8_t, Alloc>& out,
             const uint8_t* in,
             const std::vector<uint8_t, Alloc2>& in2,
             size_t n)
   {
   xor_buf(out.data(), in, in2.data(), n);
   }
 
template<typename Alloc, typename Alloc2>
std::vector<uint8_t, Alloc>&
operator^=(std::vector<uint8_t, Alloc>& out,
           const std::vector<uint8_t, Alloc2>& in)
   {
   if(out.size() < in.size())
      out.resize(in.size());
 
   xor_buf(out.data(), in.data(), in.size());
   return out;
   }
 
}
 
#endif