Re: [ros-dev] [ros-diffs] [tfaber] 74305: [NTOS:KE] - Gracefully handle page faults during V86 code execution. This is a bit of a hack because with our limited use of V86 code it is unclear how a page fault can even occur. ...

[Alex Ionescu]

So why implement this code path if we have nothing that hits it?

Best regards,
Alex Ionescu

On Fri, Apr 14, 2017 at 4:18 AM, <tfaber(a)svn.reactos.org> wrote:

>   Author: tfaber
>  Date: Fri Apr 14 11:18:22 2017
>  New Revision: 74305
>
>  URL: http://svn.reactos.org/svn/reactos?rev=74305&view=rev
>  Log:
>  [NTOS:KE]
>  - Gracefully handle page faults during V86 code execution. This is a bit
>  of a hack because with our limited use of V86 code it is unclear how a page
>  fault can even occur.
>  CORE-12993 #resolve
>
>  Modified:
>      trunk/reactos/ntoskrnl/include/internal/i386/ke.h
>      trunk/reactos/ntoskrnl/ke/i386/traphdlr.c
>      trunk/reactos/ntoskrnl/vdm/vdmexec.c
>
>  Modified: trunk/reactos/ntoskrnl/include/internal/i386/ke.h
>  URL: http://svn.reactos.org/svn/reactos/trunk/reactos/
>  ntoskrnl/include/internal/i386/ke.h?rev=74305&r1=74304&r2=74305&view=diff
>  ============================================================
>  ==================
>  --- trunk/reactos/ntoskrnl/include/internal/i386/ke.h   [iso-8859-1]
>  (original)
>  +++ trunk/reactos/ntoskrnl/include/internal/i386/ke.h   [iso-8859-1] Fri
>  Apr 14 11:18:22 2017
>  @@ -478,6 +478,12 @@
>   NTAPI
>   VdmDispatchBop(
>       IN PKTRAP_FRAME TrapFrame
>  +);
>  +
>  +BOOLEAN
>  +NTAPI
>  +VdmDispatchPageFault(
>  +    _In_ PKTRAP_FRAME TrapFrame
>   );
>
>   BOOLEAN
>
>  Modified: trunk/reactos/ntoskrnl/ke/i386/traphdlr.c
>  URL: http://svn.reactos.org/svn/reactos/trunk/reactos/
>  ntoskrnl/ke/i386/traphdlr.c?rev=74305&r1=74304&r2=74305&view=diff
>  ============================================================
>  ==================
>  --- trunk/reactos/ntoskrnl/ke/i386/traphdlr.c   [iso-8859-1] (original)
>  +++ trunk/reactos/ntoskrnl/ke/i386/traphdlr.c   [iso-8859-1] Fri Apr 14
>  11:18:22 2017
>  @@ -1304,8 +1304,20 @@
>           UNIMPLEMENTED_FATAL();
>       }
>   #endif
>  +
>       /* Check for VDM trap */
>  -    ASSERT((KiVdmTrap(TrapFrame)) == FALSE);
>  +    if (KiVdmTrap(TrapFrame))
>  +    {
>  +        DPRINT1("VDM PAGE FAULT at %lx:%lx for address %lx\n",
>  +                TrapFrame->SegCs, TrapFrame->Eip, Cr2);
>  +        if (VdmDispatchPageFault(TrapFrame))
>  +        {
>  +            /* Return and end VDM execution */
>  +            DPRINT1("VDM page fault with status 0x%lx resolved\n",
>  Status);
>  +            KiEoiHelper(TrapFrame);
>  +        }
>  +        DPRINT1("VDM page fault with status 0x%lx NOT resolved\n",
>  Status);
>  +    }
>
>       /* Either kernel or user trap (non VDM) so dispatch exception */
>       if (Status == STATUS_ACCESS_VIOLATION)
>
>  Modified: trunk/reactos/ntoskrnl/vdm/vdmexec.c
>  URL: http://svn.reactos.org/svn/reactos/trunk/reactos/
>  ntoskrnl/vdm/vdmexec.c?rev=74305&r1=74304&r2=74305&view=diff
>  ============================================================
>  ==================
>  --- trunk/reactos/ntoskrnl/vdm/vdmexec.c        [iso-8859-1] (original)
>  +++ trunk/reactos/ntoskrnl/vdm/vdmexec.c        [iso-8859-1] Fri Apr 14
>  11:18:22 2017
>  @@ -239,7 +239,7 @@
>           KeLowerIrql(OldIrql);
>           return STATUS_INVALID_SYSTEM_SERVICE;
>       }
>  -
>  +
>       /* Now do the VDM Swap */
>       VdmSwapContext(VdmFrame, &VdmTib->MonitorContext, &VdmContext);
>
>  @@ -269,7 +269,7 @@
>
>       /* Make a copy of the monitor context */
>       Context = VdmTib->MonitorContext;
>  -
>  +
>       /* Check if V86 mode was enabled or the trap was edited */
>       if ((Context.EFlags & EFLAGS_V86_MASK) || (Context.SegCs &
>  FRAME_EDITED))
>       {
>  @@ -291,7 +291,7 @@
>                   /* Remove real IF flag */
>                   VdmTib->VdmContext.EFlags &= ~EFLAGS_INTERRUPT_MASK;
>               }
>  -
>  +
>               /* Turn off VIP and VIF */
>               TrapFrame->EFlags &= ~(EFLAGS_VIP | EFLAGS_VIF);
>               VdmTib->VdmContext.EFlags &= ~(EFLAGS_VIP | EFLAGS_VIF);
>  @@ -362,4 +362,45 @@
>       return TRUE;
>   }
>
>  -
>  +BOOLEAN
>  +NTAPI
>  +VdmDispatchPageFault(
>  +    _In_ PKTRAP_FRAME TrapFrame)
>  +{
>  +    NTSTATUS Status;
>  +    PVDM_TIB VdmTib;
>  +
>  +    PAGED_CODE();
>  +
>  +    /* Get the VDM TIB so we can terminate V86 execution */
>  +    Status = VdmpGetVdmTib(&VdmTib);
>  +    if (!NT_SUCCESS(Status))
>  +    {
>  +        /* Not a proper VDM fault, keep looking */
>  +        DPRINT1("VdmDispatchPageFault: no VDM TIB, Vdm=%p\n",
>  NtCurrentTeb()->Vdm);
>  +        return FALSE;
>  +    }
>  +
>  +    /* Must be coming from V86 code */
>  +    ASSERT(TrapFrame->EFlags & EFLAGS_V86_MASK);
>  +
>  +    _SEH2_TRY
>  +    {
>  +        /* Fill out a VDM Event */
>  +        VdmTib->EventInfo.Event = VdmMemAccess;
>  +        VdmTib->EventInfo.InstructionSize = 0;
>  +
>  +        /* End VDM Execution */
>  +        VdmEndExecution(TrapFrame, VdmTib);
>  +    }
>  +    _SEH2_EXCEPT(EXCEPTION_EXECUTE_HANDLER)
>  +    {
>  +        Status = _SEH2_GetExceptionCode();
>  +    }
>  +    _SEH2_END;
>  +
>  +    /* Consider the exception handled if we succeeded */
>  +    DPRINT1("VdmDispatchPageFault EFlags %lx exit with 0x%lx\n",
>  TrapFrame->EFlags, Status);
>  +    return NT_SUCCESS(Status);
>  +}
>  +
>
>
>