libs/binder/include/binder/MemoryHeapBase.h

/*
 * Copyright (C) 2008 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

#include <stdlib.h>
#include <stdint.h>

#include <binder/Common.h>
#include <binder/IMemory.h>


namespace android {

// ---------------------------------------------------------------------------

class MemoryHeapBase : public BnMemoryHeap {
public:
    static constexpr auto MEMFD_ALLOW_SEALING_FLAG = 0x00000800;
    enum {
        READ_ONLY = IMemoryHeap::READ_ONLY,
        // memory won't be mapped locally, but will be mapped in the remote
        // process.
        DONT_MAP_LOCALLY = 0x00000100,
        NO_CACHING = 0x00000200,
        // Bypass ashmem-libcutils to create a memfd shared region.
        // Ashmem-libcutils will eventually migrate to memfd.
        // Memfd has security benefits and supports file sealing.
        // Calling process will need to modify selinux permissions to
        // open access to tmpfs files. See audioserver for examples.
        // This is only valid for size constructor.
        // For host compilation targets, memfd is stubbed in favor of /tmp
        // files so sealing is not enforced.
        FORCE_MEMFD = 0x00000400,
        // Default opt-out of sealing behavior in memfd to avoid potential DOS.
        // Clients of shared files can seal at anytime via syscall, leading to
        // TOC/TOU issues if additional seals prevent access from the creating
        // process. Alternatively, seccomp fcntl().
        MEMFD_ALLOW_SEALING = FORCE_MEMFD | MEMFD_ALLOW_SEALING_FLAG
    };

    /*
     * maps the memory referenced by fd. but DOESN'T take ownership
     * of the filedescriptor (it makes a copy with dup()
     */
    LIBBINDER_EXPORTED MemoryHeapBase(int fd, size_t size, uint32_t flags = 0, off_t offset = 0);

    /*
     * maps memory from the given device
     */
    LIBBINDER_EXPORTED explicit MemoryHeapBase(const char* device, size_t size = 0,
                                               uint32_t flags = 0);

    /*
     * maps memory from ashmem, with the given name for debugging
     * if the READ_ONLY flag is set, the memory will be writeable by the calling process,
     * but not by others. this is NOT the case with the other ctors.
     */
    LIBBINDER_EXPORTED explicit MemoryHeapBase(size_t size, uint32_t flags = 0,
                                               char const* name = nullptr);

    LIBBINDER_EXPORTED virtual ~MemoryHeapBase();

    /* implement IMemoryHeap interface */
    LIBBINDER_EXPORTED int getHeapID() const override;

    /* virtual address of the heap. returns MAP_FAILED in case of error */
    LIBBINDER_EXPORTED void* getBase() const override;

    LIBBINDER_EXPORTED size_t getSize() const override;
    LIBBINDER_EXPORTED uint32_t getFlags() const override;
    LIBBINDER_EXPORTED off_t getOffset() const override;

    LIBBINDER_EXPORTED const char* getDevice() const;

    /* this closes this heap -- use carefully */
    LIBBINDER_EXPORTED void dispose();

protected:
    LIBBINDER_EXPORTED MemoryHeapBase();
    // init() takes ownership of fd
    LIBBINDER_EXPORTED status_t init(int fd, void* base, size_t size, int flags = 0,
                                     const char* device = nullptr);

private:
    status_t mapfd(int fd, bool writeableByCaller, size_t size, off_t offset = 0);

    int         mFD;
    size_t      mSize;
    void*       mBase;
    uint32_t    mFlags;
    const char* mDevice;
    bool        mNeedUnmap;
    off_t       mOffset;
};

// ---------------------------------------------------------------------------
} // namespace android