Re: [RFC PATCH v9 03/27] x86/fpu/xstate: Introduce CET MSR XSAVES supervisor states

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On Wed, Feb 05, 2020 at 10:19:11AM -0800, Yu-cheng Yu wrote:
> Control-flow Enforcement Technology (CET) adds five MSRs.  Introduce them
> and their XSAVES supervisor states:
> 
>     MSR_IA32_U_CET (user-mode CET settings),
>     MSR_IA32_PL3_SSP (user-mode Shadow Stack pointer),
>     MSR_IA32_PL0_SSP (kernel-mode Shadow Stack pointer),
>     MSR_IA32_PL1_SSP (Privilege Level 1 Shadow Stack pointer),
>     MSR_IA32_PL2_SSP (Privilege Level 2 Shadow Stack pointer).
> 
> v6:
> - Remove __packed from struct cet_user_state, struct cet_kernel_state.
> 
> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx>

Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>

-Kees

> ---
>  arch/x86/include/asm/fpu/types.h            | 22 ++++++++++++++++++
>  arch/x86/include/asm/fpu/xstate.h           |  5 +++--
>  arch/x86/include/asm/msr-index.h            | 18 +++++++++++++++
>  arch/x86/include/uapi/asm/processor-flags.h |  2 ++
>  arch/x86/kernel/fpu/xstate.c                | 25 +++++++++++++++++++--
>  5 files changed, 68 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/include/asm/fpu/types.h b/arch/x86/include/asm/fpu/types.h
> index f098f6cab94b..d7ef4d9c7ad5 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_CET_USER,
> +	XFEATURE_CET_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_CET_USER		(1 << XFEATURE_CET_USER)
> +#define XFEATURE_MASK_CET_KERNEL	(1 << XFEATURE_CET_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
> + */
> +struct cet_user_state {
> +	u64 user_cet;			/* user control-flow settings */
> +	u64 user_ssp;			/* user shadow stack pointer */
> +};
> +
> +/*
> + * State component 12 is Control-flow Enforcement kernel states
> + */
> +struct cet_kernel_state {
> +	u64 kernel_ssp;			/* kernel shadow stack */
> +	u64 pl1_ssp;			/* privilege level 1 shadow stack */
> +	u64 pl2_ssp;			/* privilege level 2 shadow stack */
> +};
> +
>  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 9ebfdd543576..952d2515dae4 100644
> --- a/arch/x86/include/asm/fpu/xstate.h
> +++ b/arch/x86/include/asm/fpu/xstate.h
> @@ -33,13 +33,14 @@
>  				       XFEATURE_MASK_BNDCSR)
>  
>  /* All currently supported supervisor features */
> -#define SUPPORTED_XFEATURES_MASK_SUPERVISOR (0)
> +#define SUPPORTED_XFEATURES_MASK_SUPERVISOR (XFEATURE_MASK_CET_USER)
>  
>  /*
>   * Unsupported supervisor features. When a supervisor feature in this mask is
>   * supported in the future, move it to the supported supervisor feature mask.
>   */
> -#define UNSUPPORTED_XFEATURES_MASK_SUPERVISOR (XFEATURE_MASK_PT)
> +#define UNSUPPORTED_XFEATURES_MASK_SUPERVISOR (XFEATURE_MASK_PT | \
> +					       XFEATURE_MASK_CET_KERNEL)
>  
>  /* All supervisor states including supported and unsupported states. */
>  #define ALL_XFEATURES_MASK_SUPERVISOR (SUPPORTED_XFEATURES_MASK_SUPERVISOR | \
> diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
> index 084e98da04a7..114e77f5bb6b 100644
> --- a/arch/x86/include/asm/msr-index.h
> +++ b/arch/x86/include/asm/msr-index.h
> @@ -872,4 +872,22 @@
>  #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 */
> +#define MSR_IA32_CET_SHSTK_EN		0x0000000000000001ULL
> +#define MSR_IA32_CET_WRSS_EN		0x0000000000000002ULL
> +#define MSR_IA32_CET_ENDBR_EN		0x0000000000000004ULL
> +#define MSR_IA32_CET_LEG_IW_EN		0x0000000000000008ULL
> +#define MSR_IA32_CET_NO_TRACK_EN	0x0000000000000010ULL
> +#define MSR_IA32_CET_WAIT_ENDBR	0x00000000000000800UL
> +#define MSR_IA32_CET_BITMAP_MASK	0xfffffffffffff000ULL
> +
>  #endif /* _ASM_X86_MSR_INDEX_H */
> diff --git a/arch/x86/include/uapi/asm/processor-flags.h b/arch/x86/include/uapi/asm/processor-flags.h
> index bcba3c643e63..a8df907e8017 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 04f7c6b8dbbc..ec08a2b6feca 100644
> --- a/arch/x86/kernel/fpu/xstate.c
> +++ b/arch/x86/kernel/fpu/xstate.c
> @@ -38,6 +38,9 @@ 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"	,
>  };
>  
>  static short xsave_cpuid_features[] __initdata = {
> @@ -51,6 +54,9 @@ static short xsave_cpuid_features[] __initdata = {
>  	X86_FEATURE_AVX512F,
>  	X86_FEATURE_INTEL_PT,
>  	X86_FEATURE_PKU,
> +	-1,		   /* Unused */
> +	X86_FEATURE_SHSTK, /* XFEATURE_CET_USER */
> +	X86_FEATURE_SHSTK, /* XFEATURE_CET_KERNEL */
>  };
>  
>  /*
> @@ -316,6 +322,8 @@ static void __init print_xstate_features(void)
>  	print_xstate_feature(XFEATURE_MASK_ZMM_Hi256);
>  	print_xstate_feature(XFEATURE_MASK_Hi16_ZMM);
>  	print_xstate_feature(XFEATURE_MASK_PKRU);
> +	print_xstate_feature(XFEATURE_MASK_CET_USER);
> +	print_xstate_feature(XFEATURE_MASK_CET_KERNEL);
>  }
>  
>  /*
> @@ -563,6 +571,8 @@ static void check_xstate_against_struct(int nr)
>  	XCHECK_SZ(sz, nr, XFEATURE_ZMM_Hi256, struct avx_512_zmm_uppers_state);
>  	XCHECK_SZ(sz, nr, XFEATURE_Hi16_ZMM,  struct avx_512_hi16_state);
>  	XCHECK_SZ(sz, nr, XFEATURE_PKRU,      struct pkru_state);
> +	XCHECK_SZ(sz, nr, XFEATURE_CET_USER,   struct cet_user_state);
> +	XCHECK_SZ(sz, nr, XFEATURE_CET_KERNEL, struct cet_kernel_state);
>  
>  	/*
>  	 * Make *SURE* to add any feature numbers in below if
> @@ -770,8 +780,19 @@ void __init fpu__init_system_xstate(void)
>  	 * 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) ||
> +			    !boot_cpu_has(xsave_cpuid_features[i]))
> +				xfeatures_mask_all &= ~BIT_ULL(i);
> +		}
>  	}
>  
>  	xfeatures_mask_all &= fpu__get_supported_xfeatures_mask();
> -- 
> 2.21.0
> 

-- 
Kees Cook



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