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

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Date:   Sun, 11 Nov 2018 06:59:24 -0800
From:   Andy Lutomirski <luto@...capital.net>
To:     Pavel Machek <pavel@....cz>
Cc:     Borislav Petkov <bp@...en8.de>,
        Yu-cheng Yu <yu-cheng.yu@...el.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-mm@...ck.org,
        linux-arch@...r.kernel.org, linux-api@...r.kernel.org,
        Arnd Bergmann <arnd@...db.de>,
        Balbir Singh <bsingharora@...il.com>,
        Cyrill Gorcunov <gorcunov@...il.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Eugene Syromiatnikov <esyr@...hat.com>,
        Florian Weimer <fweimer@...hat.com>,
        "H.J. Lu" <hjl.tools@...il.com>, Jann Horn <jannh@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        Kees Cook <keescook@...omium.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Nadav Amit <nadav.amit@...il.com>,
        Oleg Nesterov <oleg@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Vedvyas Shanbhogue <vedvyas.shanbhogue@...el.com>
Subject: Re: [PATCH v5 04/27] x86/fpu/xstate: Add XSAVES system states for shadow stack



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