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

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Message-ID: <bb049aa9578bae7cfc6bd7c05b540f033f6685cc.camel@intel.com>
Date:   Thu, 08 Nov 2018 12:40:02 -0800
From:   Yu-cheng Yu <yu-cheng.yu@...el.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     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>,
        Andy Lutomirski <luto@...capital.net>,
        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>, Pavel Machek <pavel@....cz>,
        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 Thu, 2018-11-08 at 19:40 +0100, Borislav Petkov wrote:
> On Thu, Oct 11, 2018 at 08:15:00AM -0700, Yu-cheng Yu wrote:
> > [...] 
> > +/*
> > + * State component 11 is Control flow Enforcement user states
> 
> Why the Camel-cased naming?
> 
> "Control" then "flow" then capitalized again "Enforcement".
> 
> Fix all occurrences pls, especially the user-visible strings.

I will change it to "Control-flow Enforcement" everywhere.

> > + */
> > +struct cet_user_state {
> > +	u64 u_cet;	/* user control flow settings */
> > +	u64 user_ssp;	/* user shadow stack pointer */
> 
> Prefix both with "usr_" instead.

Ok.

> [...]
> 
> Just write "privilege level" everywhere - not "ring".
> 
> Btw, do you see how the type and the name of all those other fields in
> that file are tabulated? Except yours...

I will fix it.

[...] 
> > 
> > diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
> > index 605ec6decf3e..ad36ea28bfd1 100644
> > --- a/arch/x86/kernel/fpu/xstate.c
> > +++ b/arch/x86/kernel/fpu/xstate.c
> > @@ -35,6 +35,9 @@ static const char *xfeature_names[] =
> >  	"Processor Trace (unused)"	,
> >  	"Protection Keys User registers",
> >  	"unknown xstate feature"	,
> > +	"Control flow User registers"	,
> > +	"Control flow Kernel registers"	,
> > +	"unknown xstate feature"	,
> 
> So there are two "unknown xstate feature" array elems now...
> 
> >  static short xsave_cpuid_features[] __initdata = {
> > @@ -48,6 +51,9 @@ static short xsave_cpuid_features[] __initdata = {
> >  	X86_FEATURE_AVX512F,
> >  	X86_FEATURE_INTEL_PT,
> >  	X86_FEATURE_PKU,
> > +	0,		   /* Unused */
> 
> What's that for?

In fpu_init_system_xstate(), we test and clear features that are not enabled.
There we depend on the order of these elements.  This is the tenth "unknown
xstate feature".

Yu-cheng