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

[Edgecombe, Rick P]

On Tue, 2023-08-01 at 12:50 -0700, Sohil Mehta wrote:
> 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?

I was, but reading the docs, I think you are right. It looks like it
will be treated like a user access as far as LASS is concerned. Thanks.