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

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Date:   Thu, 8 Nov 2018 19:40:38 +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@...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, Oct 11, 2018 at 08:15:00AM -0700, Yu-cheng Yu wrote:
> Intel Control-flow Enforcement Technology (CET) introduces the
> following MSRs into the XSAVES system states.
> 
>     IA32_U_CET (user-mode CET settings),
>     IA32_PL3_SSP (user-mode shadow stack),
>     IA32_PL0_SSP (kernel-mode shadow stack),
>     IA32_PL1_SSP (ring-1 shadow stack),
>     IA32_PL2_SSP (ring-2 shadow stack).

And?

That commit message got chopped off here, it seems.

> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@...el.com>
> ---
>  arch/x86/include/asm/fpu/types.h            | 22 +++++++++++++++++++++
>  arch/x86/include/asm/fpu/xstate.h           |  4 +++-
>  arch/x86/include/uapi/asm/processor-flags.h |  2 ++
>  arch/x86/kernel/fpu/xstate.c                | 10 ++++++++++
>  4 files changed, 37 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/include/asm/fpu/types.h b/arch/x86/include/asm/fpu/types.h
> index 202c53918ecf..e55d51d172f1 100644
> --- a/arch/x86/include/asm/fpu/types.h
> +++ b/arch/x86/include/asm/fpu/types.h
> @@ -114,6 +114,9 @@ enum xfeature {
>  	XFEATURE_Hi16_ZMM,
>  	XFEATURE_PT_UNIMPLEMENTED_SO_FAR,
>  	XFEATURE_PKRU,
> +	XFEATURE_RESERVED,
> +	XFEATURE_SHSTK_USER,
> +	XFEATURE_SHSTK_KERNEL,
>  
>  	XFEATURE_MAX,
>  };
> @@ -128,6 +131,8 @@ enum xfeature {
>  #define XFEATURE_MASK_Hi16_ZMM		(1 << XFEATURE_Hi16_ZMM)
>  #define XFEATURE_MASK_PT		(1 << XFEATURE_PT_UNIMPLEMENTED_SO_FAR)
>  #define XFEATURE_MASK_PKRU		(1 << XFEATURE_PKRU)
> +#define XFEATURE_MASK_SHSTK_USER	(1 << XFEATURE_SHSTK_USER)
> +#define XFEATURE_MASK_SHSTK_KERNEL	(1 << XFEATURE_SHSTK_KERNEL)
>  
>  #define XFEATURE_MASK_FPSSE		(XFEATURE_MASK_FP | XFEATURE_MASK_SSE)
>  #define XFEATURE_MASK_AVX512		(XFEATURE_MASK_OPMASK \
> @@ -229,6 +234,23 @@ struct pkru_state {
>  	u32				pad;
>  } __packed;
>  
> +/*
> + * 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.

> + */
> +struct cet_user_state {
> +	u64 u_cet;	/* user control flow settings */
> +	u64 user_ssp;	/* user shadow stack pointer */

Prefix both with "usr_" instead.

> +} __packed;
> +
> +/*
> + * State component 12 is Control flow Enforcement kernel states
> + */
> +struct cet_kernel_state {
> +	u64 kernel_ssp;	/* kernel shadow stack */
> +	u64 pl1_ssp;	/* ring-1 shadow stack */
> +	u64 pl2_ssp;	/* ring-2 shadow stack */

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...

> +} __packed;
> +
>  struct xstate_header {
>  	u64				xfeatures;
>  	u64				xcomp_bv;
> diff --git a/arch/x86/include/asm/fpu/xstate.h b/arch/x86/include/asm/fpu/xstate.h
> index d8e2ec99f635..18b60748a34d 100644
> --- a/arch/x86/include/asm/fpu/xstate.h
> +++ b/arch/x86/include/asm/fpu/xstate.h
> @@ -28,7 +28,9 @@
>  				  XFEATURE_MASK_Hi16_ZMM | \
>  				  XFEATURE_MASK_PKRU | \
>  				  XFEATURE_MASK_BNDREGS | \
> -				  XFEATURE_MASK_BNDCSR)
> +				  XFEATURE_MASK_BNDCSR | \
> +				  XFEATURE_MASK_SHSTK_USER | \
> +				  XFEATURE_MASK_SHSTK_KERNEL)
>  
>  #ifdef CONFIG_X86_64
>  #define REX_PREFIX	"0x48, "
> diff --git a/arch/x86/include/uapi/asm/processor-flags.h b/arch/x86/include/uapi/asm/processor-flags.h
> index bcba3c643e63..25311ec4b731 100644
> --- a/arch/x86/include/uapi/asm/processor-flags.h
> +++ b/arch/x86/include/uapi/asm/processor-flags.h
> @@ -130,6 +130,8 @@
>  #define X86_CR4_SMAP		_BITUL(X86_CR4_SMAP_BIT)
>  #define X86_CR4_PKE_BIT		22 /* enable Protection Keys support */
>  #define X86_CR4_PKE		_BITUL(X86_CR4_PKE_BIT)
> +#define X86_CR4_CET_BIT		23 /* enable Control flow Enforcement */
> +#define X86_CR4_CET		_BITUL(X86_CR4_CET_BIT)
>  
>  /*
>   * x86-64 Task Priority Register, CR8
> 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?

> +	X86_FEATURE_SHSTK, /* XFEATURE_SHSTK_USER */
> +	X86_FEATURE_SHSTK, /* XFEATURE_SHSTK_KERNEL */
>  };

-- 
Regards/Gruss,
    Boris.

Good mailing practices for 400: avoid top-posting and trim the reply.