Re: [PATCH v3 00/12] Enable Linear Address Space Separation support

From: Sohil Mehta
Date: Tue Aug 01 2023 - 15:51:09 EST

On 7/31/2023 3:36 PM, Edgecombe, Rick P wrote:
> CET introduces this unusual instruction called WRUSS. It allows you to
> make user memory accesses while executing in the kernel. Because of
> this special property, the CET shadow stack patches don't toggle
> stac/clac while executing this instruction. So I think LASS will need
> it to behave more like a normal userspace access from the kernel.
> Shadow stack is not upstream yet, so just something to keep in mind for
> the future.

This is a good point. We should definitely test this out to confirm.

But, isn't WRUSS already defined as a user-mode access? So, in theory, a
user-mode access to a user address space *should* not be blocked by LASS
(even with CPL=0).

Are you suggesting that we might need to do something special for WRUSS
with LASS enabled?