Re: PMP shared permissions for S and U

Greg Favor

Note: I'm not sure if the TG's email list is up yet.  If not, check with the Security HC.

On Mon, Aug 22, 2022 at 10:02 AM Jeff Scott <jeff.scott@...> wrote:

Hi Greg,


In our world we don’t have MMU, just PMP.  The inability to supply separate permissions to S and U limits the usefulness of PMP in our environment.


I subscribed to SPMP now.  I’ll send my question to that email list as well.






From: Greg Favor <gfavor@...>
Sent: Monday, August 22, 2022 11:53 AM
To: Jeff Scott <jeff.scott@...>
Cc: tech-privileged@...
Subject: [EXT] Re: [RISC-V] [tech-privileged] PMP shared permissions for S and U


Caution: EXT Email

PMP was architected to be a mechanism to protect M-mode software and resources from non-M-mode software and devices.  This complements the MMU which serves to protect and isolate between S-mode and U-mode (and between U-mode processes).  They are intended to be orthogonal and composable architectural components.


If you are looking for something that combines those two functions into one mechanism, then take a look at the new SPMP TG that is in the process of being formed as we speak.  I'm not certain, but I think that might be what you are looking for.  (Start of group meetings, etc. will be announced on relevant RVI email lists - including the Security HC's list since I believe this TG is being sponsored by that HC.)




On Mon, Aug 22, 2022 at 9:44 AM Jeff Scott <jeff.scott@...> wrote:



I am curious why the PMP treats S and U mode accesses identically?  Is anyone aware of a standard extension that allows for different permissions for S and U?





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