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/*
* Copyright 2019 Google, Inc.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
* met: redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer;
* redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution;
* neither the name of the copyright holders nor the names of its
* contributors may be used to endorse or promote products derived from
* this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
* OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*
* Authors: Gabe Black
*/
#ifndef __MEM_BACKDOOR_HH__
#define __MEM_BACKDOOR_HH__
#include <cstdint>
#include <functional>
#include <memory>
#include "base/addr_range.hh"
#include "base/callback.hh"
class MemBackdoor
{
public:
// Callbacks from this back door are set up using a callable which accepts
// a const reference to this back door as their only parameter.
typedef std::function<void(const MemBackdoor &backdoor)> CbFunction;
private:
// This wrapper class holds the callables described above so that they
// can be stored in a generic CallbackQueue.
class Callback : public ::Callback
{
public:
Callback(MemBackdoor &bd, CbFunction cb) :
_backdoor(bd), cbFunction(cb)
{}
void process() override { cbFunction(_backdoor); }
// It looks like this is only called when the CallbackQueue is
// destroyed and this Callback is currently in the queue.
void autoDestruct() override { delete this; }
MemBackdoor &backdoor() { return _backdoor; }
private:
MemBackdoor &_backdoor;
CbFunction cbFunction;
};
public:
enum Flags{
// How data is allowed to be accessed through this backdoor.
NoAccess = 0x0,
Readable = 0x1,
Writeable = 0x2
};
// The range in the guest address space covered by this back door.
const AddrRange &range() const { return _range; }
void range(const AddrRange &r) { _range = r; }
// A pointer to the data accessible through this back door.
uint8_t *ptr() const { return _ptr; }
void ptr(uint8_t *p) { _ptr = p; }
/*
* Helper functions to make it easier to set/check particular flags.
*/
bool readable() const { return _flags & Readable; }
void
readable(bool r)
{
if (r)
_flags = (Flags)(_flags | Readable);
else
_flags = (Flags)(_flags & ~Readable);
}
bool writeable() const { return _flags & Writeable; }
void
writeable(bool w)
{
if (w)
_flags = (Flags)(_flags | Writeable);
else
_flags = (Flags)(_flags & ~Writeable);
}
Flags flags() const { return _flags; }
void flags(Flags f) { _flags = f; }
MemBackdoor(AddrRange r, uint8_t *p, Flags flags) :
invalidationCallbacks(new CallbackQueue),
_range(r), _ptr(p), _flags(flags)
{}
MemBackdoor() : MemBackdoor(AddrRange(), nullptr, NoAccess)
{}
// Set up a callable to be called when this back door is invalidated. This
// lets holders update their bookkeeping to remove any references to it,
// and/or to propogate that invalidation to other interested parties.
void
addInvalidationCallback(CbFunction func)
{
auto *cb = new MemBackdoor::Callback(*this, func);
assert(cb);
invalidationCallbacks->add(cb);
}
// Notify and clear invalidation callbacks when the data in the backdoor
// structure is no longer valid/current. The backdoor might then be
// updated or even deleted without having to worry about stale data being
// used.
void
invalidate()
{
invalidationCallbacks->process();
// Delete and recreate the callback queue to ensure the callback
// objects are deleted.
invalidationCallbacks.reset(new CallbackQueue());
}
private:
std::unique_ptr<CallbackQueue> invalidationCallbacks;
AddrRange _range;
uint8_t *_ptr;
Flags _flags;
};
typedef MemBackdoor *MemBackdoorPtr;
#endif //__MEM_BACKDOOR_HH__
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