linux-kernel - Re: [PATCH v15 03/26] x86/fpu/xstate: Introduce CET MSR XSAVES supervisor states

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Date:   Thu, 26 Nov 2020 12:02:15 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Yu-cheng Yu <yu-cheng.yu@...el.com>
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@...nel.org>,
        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>,
        Dave Martin <Dave.Martin@....com>,
        Weijiang Yang <weijiang.yang@...el.com>,
        Pengfei Xu <pengfei.xu@...el.com>
Subject: Re: [PATCH v15 03/26] x86/fpu/xstate: Introduce CET MSR XSAVES
 supervisor states

On Tue, Nov 10, 2020 at 08:21:48AM -0800, Yu-cheng Yu wrote:
> diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
> index 972a34d93505..6f05ab2a1fa4 100644
> --- a/arch/x86/include/asm/msr-index.h
> +++ b/arch/x86/include/asm/msr-index.h
> @@ -922,4 +922,24 @@
>  #define MSR_VM_IGNNE                    0xc0010115
>  #define MSR_VM_HSAVE_PA                 0xc0010117
>  
> +/* Control-flow Enforcement Technology MSRs */
> +#define MSR_IA32_U_CET		0x6a0 /* user mode cet setting */
> +#define MSR_IA32_S_CET		0x6a2 /* kernel mode cet setting */
> +#define MSR_IA32_PL0_SSP	0x6a4 /* kernel shstk pointer */
> +#define MSR_IA32_PL1_SSP	0x6a5 /* ring-1 shstk pointer */
> +#define MSR_IA32_PL2_SSP	0x6a6 /* ring-2 shstk pointer */
> +#define MSR_IA32_PL3_SSP	0x6a7 /* user shstk pointer */
> +#define MSR_IA32_INT_SSP_TAB	0x6a8 /* exception shstk table */
> +
> +/* MSR_IA32_U_CET and MSR_IA32_S_CET bits */

Pls put the bit defines under the MSRs they belong to.

> +#define CET_SHSTK_EN		BIT_ULL(0)
> +#define CET_WRSS_EN		BIT_ULL(1)
> +#define CET_ENDBR_EN		BIT_ULL(2)
> +#define CET_LEG_IW_EN		BIT_ULL(3)
> +#define CET_NO_TRACK_EN		BIT_ULL(4)
> +#define CET_SUPPRESS_DISABLE	BIT_ULL(5)
> +#define CET_RESERVED		(BIT_ULL(6) | BIT_ULL(7) | BIT_ULL(8) | BIT_ULL(9))
> +#define CET_SUPPRESS		BIT_ULL(10)
> +#define CET_WAIT_ENDBR		BIT_ULL(11)

...

>  	 * Clear XSAVE features that are disabled in the normal CPUID.
>  	 */
>  	for (i = 0; i < ARRAY_SIZE(xsave_cpuid_features); i++) {
> -		if (!boot_cpu_has(xsave_cpuid_features[i]))
> -			xfeatures_mask_all &= ~BIT_ULL(i);
> +		if (xsave_cpuid_features[i] == X86_FEATURE_SHSTK) {
> +			/*
> +			 * X86_FEATURE_SHSTK and X86_FEATURE_IBT share
> +			 * same states, but can be enabled separately.
> +			 */
> +			if (!boot_cpu_has(X86_FEATURE_SHSTK) &&
> +			    !boot_cpu_has(X86_FEATURE_IBT))
> +				xfeatures_mask_all &= ~BIT_ULL(i);
> +		} else {
> +			if ((xsave_cpuid_features[i] == -1) ||
			     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

That is a new check. I guess it could be done first to simplify the
code:

	for (i = 0; i < ARRAY_SIZE(xsave_cpuid_features); i++) {
		if (xsave_cpuid_features[i] == -1) {
			xfeatures_mask_all &= ~BIT_ULL(i);
			continue;
		}

		/* the rest of the bla */

Yes?

-- 
Regards/Gruss,
    Boris.

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