From: Anders Fogh [afogh@flaffer.com]
Sent: Friday, February 23, 2001 3:42 AM
To: NT Developers Interest List
Subject: [ntdev] Re: Calling Interrupt vector of the IDT from User-mode

Hello Frederick,

There is no reason why you cannot call an interupt from ring
3 the way you do. (NTdll.dll relies heavily on calling interupts 2e &
2d from usermode just like you do) However the interupt might be protected by having
the DPL set to 0 which means you can only use it from ring 0. Under
Windows 2000 only interupts 1,3,4 and 2a-2eh have DPL = 3.  So unless
you specifically change the DPL bits in the int 31h gate you'll get an
exception trying to invoke the interupt. (If you do set the DPL=3 and
then invoke the interupt you will be likely to crash system - the
protection is there for a reason).

regards,
Anders Fogh


Thursday, February 22, 2001, 2:28:26 PM, you wrote:


FC> Hi ,

FC>         I'm just trying to call an interrupt vector of the IDT from the Ring 3 with
FC> the assembler command
FC> _asm {     int  0x31  } but I got a message box: "  The instruction at
FC> "0x00401d80" referenced memory
FC> at 0xffffffff . The memory could not be read.

FC> I don't know if it's possible to make that kind of call from the User-mode.
FC> If it's possible what did I need to do to make it work properly?
FC>  I'm using Windows NT 2000 and I'm sure that the Interrupt vector is valid.
FC> Do you have any hint that could help me????

FC> Thanks

FC> Frederick Champoux


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-- 
Best regards,
 Anders                            mailto:afogh@flaffer.com



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