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

[Andy Lutomirski]

> On Nov 11, 2018, at 3:31 AM, Pavel Machek <pa...@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.

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.

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