/*

 * Copyright (c) 2014, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 *

 */

#ifndef SHARE_VM_MEMORY_GUARDED_MEMORY_HPP

#define SHARE_VM_MEMORY_GUARDED_MEMORY_HPP

#include "memory/allocation.hpp"

#include "utilities/globalDefinitions.hpp"

/**

 * Guarded memory for detecting buffer overrun.

 *

 * Allows allocations to be wrapped with padded bytes of a known byte pattern,

 * that is a "guard". Guard patterns may be verified to detect buffer overruns.

 *

 * Primarily used by "debug malloc" and "checked JNI".

 *

 * Memory layout:

 *

 * |Offset             | Content              | Description    |

 * |------------------------------------------------------------

 * |base_addr          | 0xABABABABABABABAB   | Head guard     |

 * |+16                | <size_t:user_size>   | User data size |

 * |+sizeof(uintptr_t) | <tag>                | Tag word       |

 * |+sizeof(void*)     | 0xF1 <user_data> (   | User data      |

 * |+user_size         | 0xABABABABABABABAB   | Tail guard     |

 * -------------------------------------------------------------

 *

 * Where:

 *  - guard padding uses "badResourceValue" (0xAB)

 *  - tag word is general purpose

 *  - user data

 *    -- initially padded with "uninitBlockPad" (0xF1),

 *    -- to "freeBlockPad" (0xBA), when freed

 *

 * Usage:

 *

 * * Allocations: one may wrap allocations with guard memory:

 * <code>

 *   Thing* alloc_thing() {

 *     void* mem = user_alloc_fn(GuardedMemory::get_total_size(sizeof(thing)));

 *     GuardedMemory guarded(mem, sizeof(thing));

 *     return (Thing*) guarded.get_user_ptr();

 *   }

 * </code>

 * * Verify: memory guards are still in tact

 * <code>

 *   bool verify_thing(Thing* thing) {

 *     GuardedMemory guarded((void*)thing);

 *     return guarded.verify_guards();

 *   }

 * </code>

 * * Free: one may mark bytes as freed (further debugging support)

 * <code>

 *   void free_thing(Thing* thing) {

 *    GuardedMemory guarded((void*)thing);

 *    assert(guarded.verify_guards(), "Corrupt thing");

 *    user_free_fn(guards.release_for_freeing();

 *   }

 * </code>

 */

class GuardedMemory : StackObj { // Wrapper on stack

  // Private inner classes for memory layout...

protected:

  /**

   * Guard class for header and trailer known pattern to test for overwrites.

   */

  class Guard { // Class for raw memory (no vtbl allowed)

    friend class GuardedMemory;

   protected:

    enum {

      GUARD_SIZE = 16

    };

    u_char _guard[GUARD_SIZE];

   public:

    void build() {

      u_char* c = _guard; // Possibly unaligned if tail guard

      u_char* end = c + GUARD_SIZE;

      while (c < end) {

        *c = badResourceValue;

        c++;

      }

    }

    bool verify() const {

      u_char* c = (u_char*) _guard;

      u_char* end = c + GUARD_SIZE;

      while (c < end) {

        if (*c != badResourceValue) {

          return false;

        }

        c++;

      }

      return true;

    }

  }; // GuardedMemory::Guard

  /**

   * Header guard and size

   */

  class GuardHeader : Guard {

    friend class GuardedMemory;

   protected:

    // Take care in modifying fields here, will effect alignment

    // e.g. x86 ABI 16 byte stack alignment

    union {

      uintptr_t __unused_full_word1;

      size_t _user_size;

    };

    void* _tag;

   public:

    void set_user_size(const size_t usz) { _user_size = usz; }

    size_t get_user_size() const { return _user_size; }

    void set_tag(const void* tag) { _tag = (void*) tag; }

    void* get_tag() const { return _tag; }

  }; // GuardedMemory::GuardHeader

  // Guarded Memory...

 protected:

  u_char* _base_addr;

 public:

  /**

   * Create new guarded memory.

   *

   * Wraps, starting at the given "base_ptr" with guards. Use "get_user_ptr()"

   * to return a pointer suitable for user data.

   *

   * @param base_ptr  allocation wishing to be wrapped, must be at least "GuardedMemory::get_total_size()" bytes.

   * @param user_size the size of the user data to be wrapped.

   * @param tag       optional general purpose tag.

   */

  GuardedMemory(void* base_ptr, const size_t user_size, const void* tag = NULL) {

    wrap_with_guards(base_ptr, user_size, tag);

  }

  /**

   * Wrap existing guarded memory.

   *

   * To use this constructor, one must have created guarded memory with

   * "GuardedMemory(void*, size_t, void*)" (or indirectly via helper, e.g. "wrap_copy()").

   *

   * @param user_p  existing wrapped memory.

   */

  GuardedMemory(void* userp) {

    u_char* user_ptr = (u_char*) userp;

    assert((uintptr_t)user_ptr > (sizeof(GuardHeader) + 0x1000), "Invalid pointer");

    _base_addr = (user_ptr - sizeof(GuardHeader));

  }

  /**

   * Create new guarded memory.

   *

   * Wraps, starting at the given "base_ptr" with guards. Allows reuse of stack allocated helper.

   *

   * @param base_ptr  allocation wishing to be wrapped, must be at least "GuardedMemory::get_total_size()" bytes.

   * @param user_size the size of the user data to be wrapped.

   * @param tag       optional general purpose tag.

   *

   * @return user data pointer (inner pointer to supplied "base_ptr").

   */

  void* wrap_with_guards(void* base_ptr, size_t user_size, const void* tag = NULL) {

    assert(base_ptr != NULL, "Attempt to wrap NULL with memory guard");

    _base_addr = (u_char*)base_ptr;

    get_head_guard()->build();

    get_head_guard()->set_user_size(user_size);

    get_tail_guard()->build();

    set_tag(tag);

    set_user_bytes(uninitBlockPad);

    assert(verify_guards(), "Expected valid memory guards");

    return get_user_ptr();

  }

  /**

   * Verify head and tail guards.

   *

   * @return true if guards are intact, false would indicate a buffer overrun.

   */

  bool verify_guards() const {

    if (_base_addr != NULL) {

      return (get_head_guard()->verify() && get_tail_guard()->verify());

    }

    return false;

  }

  /**

   * Set the general purpose tag.

   *

   * @param tag general purpose tag.

   */

  void set_tag(const void* tag) { get_head_guard()->set_tag(tag); }

  /**

   * Return the general purpose tag.

   *

   * @return the general purpose tag, defaults to NULL.

   */

  void* get_tag() const { return get_head_guard()->get_tag(); }

  /**

   * Return the size of the user data.

   *

   * @return the size of the user data.

   */

  size_t get_user_size() const {

    return get_head_guard()->get_user_size();

  }

  /**

   * Return the user data pointer.

   *

   * @return the user data pointer.

   */

  u_char* get_user_ptr() const {

    return _base_addr + sizeof(GuardHeader);

  }

  /**

   * Release the wrapped pointer for resource freeing.

   *

   * Pads the user data with "freeBlockPad", and dis-associates the helper.

   *

   * @return the original base pointer used to wrap the data.

   */

  void* release_for_freeing() {

    set_user_bytes(freeBlockPad);

    return release();

  }

  /**

   * Dis-associate the help from the original base address.

   *

   * @return the original base pointer used to wrap the data.

   */

  void* release() {

    void* p = (void*) _base_addr;

    _base_addr = NULL;

    return p;

  }

  virtual void print_on(outputStream* st) const;

 protected:

  GuardHeader*  get_head_guard() const { return (GuardHeader*) _base_addr; }

  Guard*        get_tail_guard() const { return (Guard*) (get_user_ptr() + get_user_size()); };

  void set_user_bytes(u_char ch) {

    memset(get_user_ptr(), ch, get_user_size());

  }

  /**

   * Return the total size required for wrapping the given user size.

   *

   * @return the total size required for wrapping the given user size.

   */

  static size_t get_total_size(size_t user_size) {

    size_t total_size = sizeof(GuardHeader) + user_size + sizeof(Guard);

    assert(total_size > user_size, "Unexpected wrap-around");

    return total_size;

  }

  // Helper functions...

  /**

   * Wrap a copy of size "len" of "ptr".

   *

   * @param ptr the memory to be copied

   * @param len the length of the copy

   * @param tag optional general purpose tag (see GuardedMemory::get_tag())

   *

   * @return guarded wrapped memory pointer to the user area, or NULL if OOM.

   */

  static void* wrap_copy(const void* p, const size_t len, const void* tag = NULL);

  /**

   * Free wrapped copy.

   *

   * Frees memory copied with "wrap_copy()".

   *

   * @param p memory returned by "wrap_copy()".

   *

   * @return true if guards were verified as intact. false indicates a buffer overrun.

   */

  static bool free_copy(void* p);

  // Testing...

#ifndef PRODUCT

  static void test_guarded_memory(void);

#endif

}; // GuardedMemory

#endif // SHARE_VM_MEMORY_GUARDED_MEMORY_HPP