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

Kees Cook
2020-02-25T20:04:23Z

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@intel.com>

Reviewed-by: Kees Cook <keescook@chromium.org>

-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