Re: MPIE and MPP update when returning from interrupt with MRET
Bill Huffman
When an exception or an ECALL arrives at its handler, the privilege of the code running before the exception/ECALL is always available in MPP or SPP.
Bill
From: tech-privileged@... <tech-privileged@...>
On Behalf Of Allen Baum
EXTERNAL MAIL This is in the priv spec sec 3.1.6.1 - just search for mret. My explanation of why MPP reverts to Umode is to prevent privilege escalation if you go off the end of the 1-deep privilege level stack. Whichever mode you return to, you can always set PP to either your own mode, or a lower priv level, but not higher, and this ensures it doesn't start out higher.
The absence of which mode you are in is quite deliberate: its existence is a virtualization hole.
On Tue, Dec 15, 2020 at 11:48 AM Richard Trauben <rtrauben@...> wrote:
|
|