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

Yu-cheng Yu
2018-11-08T20:40:02Z

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