linux-kernel - Re: [RFC PATCH v4 01/27] x86/cpufeatures: Add CPUIDs for Control-flow Enforcement Technology (CET)

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Date:   Fri, 28 Sep 2018 18:51:18 +0200
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@...capital.net>,
        Balbir Singh <bsingharora@...il.com>,
        Cyrill Gorcunov <gorcunov@...il.com>,
        Dave Hansen <dave.hansen@...ux.intel.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: [RFC PATCH v4 01/27] x86/cpufeatures: Add CPUIDs for
 Control-flow Enforcement Technology (CET)

On Fri, Sep 21, 2018 at 08:03:25AM -0700, Yu-cheng Yu wrote:
> Add CPUIDs for Control-flow Enforcement Technology (CET).
> 
> CPUID.(EAX=7,ECX=0):ECX[bit 7] Shadow stack
> CPUID.(EAX=7,ECX=0):EDX[bit 20] Indirect branch tracking
> 
> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@...el.com>
> ---
>  arch/x86/include/asm/cpufeatures.h | 2 ++
>  arch/x86/kernel/cpu/scattered.c    | 1 +
>  2 files changed, 3 insertions(+)
> 
> diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
> index 89a048c2faec..fa69651a017e 100644
> --- a/arch/x86/include/asm/cpufeatures.h
> +++ b/arch/x86/include/asm/cpufeatures.h
> @@ -221,6 +221,7 @@
>  #define X86_FEATURE_ZEN			( 7*32+28) /* "" CPU is AMD family 0x17 (Zen) */
>  #define X86_FEATURE_L1TF_PTEINV		( 7*32+29) /* "" L1TF workaround PTE inversion */
>  #define X86_FEATURE_IBRS_ENHANCED	( 7*32+30) /* Enhanced IBRS */
> +#define X86_FEATURE_IBT			( 7*32+31) /* Indirect Branch Tracking */
>  
>  /* Virtualization flags: Linux defined, word 8 */
>  #define X86_FEATURE_TPR_SHADOW		( 8*32+ 0) /* Intel TPR Shadow */
> @@ -321,6 +322,7 @@
>  #define X86_FEATURE_PKU			(16*32+ 3) /* Protection Keys for Userspace */
>  #define X86_FEATURE_OSPKE		(16*32+ 4) /* OS Protection Keys Enable */
>  #define X86_FEATURE_AVX512_VBMI2	(16*32+ 6) /* Additional AVX512 Vector Bit Manipulation Instructions */
> +#define X86_FEATURE_SHSTK		(16*32+ 7) /* Shadow Stack */
>  #define X86_FEATURE_GFNI		(16*32+ 8) /* Galois Field New Instructions */
>  #define X86_FEATURE_VAES		(16*32+ 9) /* Vector AES */
>  #define X86_FEATURE_VPCLMULQDQ		(16*32+10) /* Carry-Less Multiplication Double Quadword */
> diff --git a/arch/x86/kernel/cpu/scattered.c b/arch/x86/kernel/cpu/scattered.c
> index 772c219b6889..63cbb4d9938e 100644
> --- a/arch/x86/kernel/cpu/scattered.c
> +++ b/arch/x86/kernel/cpu/scattered.c
> @@ -21,6 +21,7 @@ struct cpuid_bit {
>  static const struct cpuid_bit cpuid_bits[] = {
>  	{ X86_FEATURE_APERFMPERF,       CPUID_ECX,  0, 0x00000006, 0 },
>  	{ X86_FEATURE_EPB,		CPUID_ECX,  3, 0x00000006, 0 },
> +	{ X86_FEATURE_IBT,		CPUID_EDX, 20, 0x00000007, 0},

If you haven't noticed, there's already a separate leaf:

/* Intel-defined CPU features, CPUID level 0x00000007:0 (EDX), word 18 */

in arch/x86/include/asm/cpufeatures.h

-- 
Regards/Gruss,
    Boris.

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