Re: PMP shared permissions for S and U


Greg Favor
 

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.)

Greg

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

Hello,

 

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?

 

Thanks,

 

Jeff

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