To ask questions about priviledge change

[leetow2003]

The first I use instruction RETF from 0 ring to 3 ring,then I use calling gate
from ring 3 to ring 0,I want to know:
(1) These code segments are 32-bit segments,
so the stack segments must be 32-bit segmnet,is my opinion right?
(2) The DPL of calling gate is 3,its RPL must be 3,
is my opinion right?

[egos]

(1) These code segments are 32-bit segments, so the stack segments must be 32-bit segmnet,is my opinion right?

Yes. And esp value should be multiple of 4 bytes.

(2) The DPL of calling gate is 3,its RPL must be 3, is my opinion right?

No. Here the same rule applies as for data access: Max(CPL, RPL) <= DPL (usually CPL=RPL). I.e. you can use same gate to transfer control to the kernel from any privilege level if its DPL=3.

[rdos]

(1) These code segments are 32-bit segments, so the stack segments must be 32-bit segmnet,is my opinion right?

Yes. And esp value should be multiple of 4 bytes.

No. A 32-bit application can have a 16-bit kernel stack (for instance). The bitness of the stack segment only determines if the processor uses SP or ESP.

A segmented, 32-bit, application could also theoretically have a 16-bit stack segment. The code would not be dependent on this. Size for pushes are determined by code segment bitness, not stack segment bitness.