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

From: Pavel Machek <pavel@ucw.cz>
To: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>,
	Yu-cheng Yu <yu-cheng.yu@intel.com>,
	x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>,
	linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
	linux-mm@kvack.org, linux-arch@vger.kernel.org,
	linux-api@vger.kernel.org, Arnd Bergmann <arnd@arndb.de>,
	Balbir Singh <bsingharora@gmail.com>,
	Cyrill Gorcunov <gorcunov@gmail.com>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Eugene Syromiatnikov <esyr@redhat.com>,
	Florian Weimer <fweimer@redhat.com>,
	"H.J. Lu" <hjl.tools@gmail.com>, Jann Horn <jannh@google.com>,
	Jonathan Corbet <corbet@lwn.net>,
	Kees Cook <keescook@chromium.org>,
	Mike Kravetz <mike.kravetz@oracle.com>,
	Nadav Amit <nadav.amit@gmail.com>,
	Oleg Nesterov <oleg@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Randy Dunlap <rdunlap@infradead.org>,
	"Ravi V. Shankar" <ravi.v.shankar@intel.com>,
	Vedvyas Shanbhogue <vedvyas.shanbhogue@intel.com>
Subject: Re: [PATCH v5 04/27] x86/fpu/xstate: Add XSAVES system states for shadow stack
Date: Sun, 11 Nov 2018 20:02:30 +0100	[thread overview]
Message-ID: <20181111190230.GA2681@amd> (raw)
Message-ID: <20181111190230.D35MPrIVAIH7j5gNkBaXAGDvoXYmL_6woFW-nhIwbfc@z> (raw)
In-Reply-To: <4E917DA9-5192-48E2-8857-08C3ABE08AFE@amacapital.net>

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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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