Re: [PATCH v17 04/26] x86/cpufeatures: Introduce X86_FEATURE_CET and setup functions

[Yu, Yu-cheng]

On 1/11/2021 9:56 AM, Borislav Petkov wrote:
> On Tue, Dec 29, 2020 at 01:30:31PM -0800, Yu-cheng Yu wrote:
> > @@ -895,6 +903,12 @@ static void init_speculation_control(struct cpuinfo_x86 *c)
> >   	}
> >   }
> >   
> > +static void init_cet_features(struct cpuinfo_x86 *c)
> > +{
> > +	if (cpu_has(c, X86_FEATURE_SHSTK) || cpu_has(c, X86_FEATURE_IBT))
> > +		set_cpu_cap(c, X86_FEATURE_CET);
> > +}
>
> No need for that function - just add this two-liner to bsp_init_intel()
> and not in get_cpu_cap().

I will move these to bsp_init_intel(), and change to:

if (cpu_has(c, X86_FEATURE_SHSTK) || cpu_has(c, X86_FEATURE_IBT))
	setup_force_cpu_cap(X86_FEATURE_CET);

> > +static void adjust_combined_cpu_features(void)
> > +{
> > +#ifdef CONFIG_X86_CET_USER
> > +	if (test_bit(X86_FEATURE_SHSTK, (unsigned long *)cpu_caps_cleared) &&
> > +	    test_bit(X86_FEATURE_IBT, (unsigned long *)cpu_caps_cleared))
> > +		setup_clear_cpu_cap(X86_FEATURE_CET);
> > +#endif
>
> There's no need for this function...
>
> > +}
> > +
> >   /*
> >    * We parse cpu parameters early because fpu__init_system() is executed
> >    * before parse_early_param().
> > @@ -1252,9 +1276,19 @@ static void __init cpu_parse_early_param(void)
> >   	if (cmdline_find_option_bool(boot_command_line, "noxsaves"))
> >   		setup_clear_cpu_cap(X86_FEATURE_XSAVES);
> >   
> > +	/*
> > +	 * CET states are XSAVES states and options must be parsed early.
> > +	 */
> > +#ifdef CONFIG_X86_CET_USER
> > +	if (cmdline_find_option_bool(boot_command_line, "no_user_shstk"))
> > +		setup_clear_cpu_cap(X86_FEATURE_SHSTK);
>
> ... when you can do
>
> 	setup_clear_cpu_cap(X86_FEATURE_CET);
>
> here and...
>
> > +	if (cmdline_find_option_bool(boot_command_line, "no_user_ibt"))
> > +		setup_clear_cpu_cap(X86_FEATURE_IBT);
>
> ... here.

Two problems here.  X86_FEATURE_CET indicates either CET features is 
enabled, not both.  Also, "clearcpuid" can has CET features.  However, 
since X86_FEATURE_CET is now set in bsp_init_intel() (after 
cpu_parse_early_params()), I think, adjust_combined_cpu_features() can 
be removed.  I will test it.

--
Thanks,
Yu-cheng