Re: [PATCH v5 04/27] x86/fpu/xstate: Add XSAVES system states for shadow stack

Pavel Machek
2018-11-11T19:02:30Z

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On Sun 2018-11-11 06:59:24, Andy Lutomirski wrote:
>
>
> > On Nov 11, 2018, at 3:31 AM, Pavel Machek <pavel@ucw.cz> wrote:
> >
> > Hi!
> >
> >>> +/*
> >>> + * State component 12 is Control flow Enforcement kernel states
> >>> + */
> >>> +struct cet_kernel_state {
> >>> + u64 kernel_ssp; /* kernel shadow stack */
> >>> + u64 pl1_ssp; /* ring-1 shadow stack */
> >>> + u64 pl2_ssp; /* ring-2 shadow stack */
> >>
> >> Just write "privilege level" everywhere - not "ring".
> >
> > Please just use word "ring". It is well estabilished terminology.
> >
> > Which ring is priviledge level 1, given that we have SMM and
> > virtualization support?
>
> To the contrary: CPL, DPL, and RPL are very well defined terms in the architecture manuals. “PL” is privilege level. PL 1 is very well defined.
>

"Priviledge level" is generic term. "CPL" I may recognize as
Intel-specific. "priviledge level" I would not. So I'd really use
"ring" there. "CPL 1 shadow stack" would be okay, too I guess.

> SMM is SMM, full stop (unless dual mode or whatever it’s called is on, but AFAIK no one uses it). VMX non-root CPL 1 is *still* privilege level 1.
>
> In contrast, the security community likes to call SMM “ring -1”, which is cute, but wrong from a systems programmer view. For example, SMM’s CPL can still range from 0-3.
>

Regards,
Pavel
--
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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