1/*
2 * Copyright 2019 Google, Inc.
3 *
4 * Redistribution and use in source and binary forms, with or without
5 * modification, are permitted provided that the following conditions are
6 * met: redistributions of source code must retain the above copyright
7 * notice, this list of conditions and the following disclaimer;
8 * redistributions in binary form must reproduce the above copyright
9 * notice, this list of conditions and the following disclaimer in the
10 * documentation and/or other materials provided with the distribution;
11 * neither the name of the copyright holders nor the names of its
12 * contributors may be used to endorse or promote products derived from
13 * this software without specific prior written permission.
14 *
15 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
16 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
17 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
18 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
19 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
20 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
21 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
22 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
23 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
24 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
25 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
26 *
27 * Authors: Gabe Black
28 */
29
30#ifndef __MEM_BACKDOOR_HH__
31#define __MEM_BACKDOOR_HH__
32
33#include <cstdint>
34#include <functional>
35#include <memory>
36
37#include "base/addr_range.hh"
38#include "base/callback.hh"
39
40class MemBackdoor
41{
42  public:
43    // Callbacks from this back door are set up using a callable which accepts
44    // a const reference to this back door as their only parameter.
45    typedef std::function<void(const MemBackdoor &backdoor)> CbFunction;
46
47  private:
48    // This wrapper class holds the callables described above so that they
49    // can be stored in a generic CallbackQueue.
50    class Callback : public ::Callback
51    {
52      public:
53        Callback(MemBackdoor &bd, CbFunction cb) :
54            _backdoor(bd), cbFunction(cb)
55        {}
56
57        void process() override { cbFunction(_backdoor); }
58        // It looks like this is only called when the CallbackQueue is
59        // destroyed and this Callback is currently in the queue.
60        void autoDestruct() override { delete this; }
61
62        MemBackdoor &backdoor() { return _backdoor; }
63
64      private:
65        MemBackdoor &_backdoor;
66        CbFunction cbFunction;
67    };
68
69  public:
70    enum Flags{
71        // How data is allowed to be accessed through this backdoor.
72        NoAccess = 0x0,
73        Readable = 0x1,
74        Writeable = 0x2
75    };
76
77    // The range in the guest address space covered by this back door.
78    const AddrRange &range() const { return _range; }
79    void range(const AddrRange &r) { _range = r; }
80
81    // A pointer to the data accessible through this back door.
82    uint8_t *ptr() const { return _ptr; }
83    void ptr(uint8_t *p) { _ptr = p; }
84
85    /*
86     * Helper functions to make it easier to set/check particular flags.
87     */
88
89    bool readable() const { return _flags & Readable; }
90    void
91    readable(bool r)
92    {
93        if (r)
94            _flags = (Flags)(_flags | Readable);
95        else
96            _flags = (Flags)(_flags & ~Readable);
97    }
98
99    bool writeable() const { return _flags & Writeable; }
100    void
101    writeable(bool w)
102    {
103        if (w)
104            _flags = (Flags)(_flags | Writeable);
105        else
106            _flags = (Flags)(_flags & ~Writeable);
107    }
108
109    Flags flags() const { return _flags; }
110    void flags(Flags f) { _flags = f; }
111
112    MemBackdoor(AddrRange r, uint8_t *p, Flags flags) :
113        invalidationCallbacks(new CallbackQueue),
114        _range(r), _ptr(p), _flags(flags)
115    {}
116
117    MemBackdoor() : MemBackdoor(AddrRange(), nullptr, NoAccess)
118    {}
119
120    // Set up a callable to be called when this back door is invalidated. This
121    // lets holders update their bookkeeping to remove any references to it,
122    // and/or to propogate that invalidation to other interested parties.
123    void
124    addInvalidationCallback(CbFunction func)
125    {
126        auto *cb = new MemBackdoor::Callback(*this, func);
127        assert(cb);
128        invalidationCallbacks->add(cb);
129    }
130
131    // Notify and clear invalidation callbacks when the data in the backdoor
132    // structure is no longer valid/current. The backdoor might then be
133    // updated or even deleted without having to worry about stale data being
134    // used.
135    void
136    invalidate()
137    {
138        invalidationCallbacks->process();
139        // Delete and recreate the callback queue to ensure the callback
140        // objects are deleted.
141        invalidationCallbacks.reset(new CallbackQueue());
142    }
143
144  private:
145    std::unique_ptr<CallbackQueue> invalidationCallbacks;
146
147    AddrRange _range;
148    uint8_t *_ptr;
149    Flags _flags;
150};
151
152typedef MemBackdoor *MemBackdoorPtr;
153
154#endif  //__MEM_BACKDOOR_HH__
155