New subject: [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. ...

14 Apr 2017

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@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);

+}




    

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. ...