???????????????????????????????????????????????????????????????? ??????????????????????????????? Intel ??80286?????cpu??????4???????(???????) ??0????3??????????????С??????e?????????0???????????????????λ??1??2????3?????????????????????′???????????????????? ????????????????????????????????????????????????????????????????????????????????????????????????????????????? ?????ó????????????á?????Intel??????????

????1.????????????????????????????????????

????2.???????????????????????????????????????

???????????????????????????????????????RPL??DPL??CPL????????

????Intel????DPL??RPL??CPL?????????????顣

????DPL?????????????Descriptor Privilege Level??

?????? ???????????е????λ??????????????????????????????????????????????????????????????????(Data??Code??Stack)?????? ?????code?ε????????????￡????????????????ú???????????????????——???DPL????????????????ε?DPL???????

????RPL???????????RPL(Request Privilege Level)

????RPL???????????????λ?? RPL ???????????η???????????????????????????????????? RPL ?? ? ????????????????????????????RPL>=CPL???????RPL<CPL???????????????CPL??????????????????????? ???EPL=max(RPL??CPL)<=DPL????????????RPL???????????η??????????????RPL=0?????????С??RPL=3??? ???????????????????????????????rpl???????????cpl??????Ρ?

????????????????????????????????????????????????????????????CPU????飬?????????С??????????RPL???????????????????????????????——??Щ?????????????????????????????????????????????RPL????????????

???????????????????rpl?????????????Ρ?Intel??????ж?RPL????????????????????????

????The RPL can be used to insure that privileged code does not access a segment on behalf of an application program unless the program itself has access privileges for that segment.

??????????????Щ???????λ?????????????????????????Щ??

???????????????????RPL???????????????С???????Щ????Ρ??????????????A??CPL=0?????????????н???B??DPL=3???????????C??DPL=2??????????????????CPL>2??????????

?????????????????A???????????????RPL????????????????y???A?????????C??????? ???????????????????????????????????????C???????????????????н???B????????????????????????????????????????????????? ????????????????????DPL???????????????????y???B????????е????????????????н???B??DPL??RPL??????????????C?????????????????????????????????????B??DPL???A????????У????????A??????????C??

????CPL??????????????Current Privilege Level??

?????? ??????????е?????????????????CPL??????CS?е????λ???????CS??????????????????CS??????????????????е?RPL????? CPL?????????λ??????????????CS???????????????????????????——???????????????????????????????????

???????????????????????RPL???????????CPL????????????е???????????????????????????CPL.

??????????????CS??SS????????????????????????DS??ES??FS??GS???????INTEL??и?????????????????????????????y???????????????????????RPL??