Re: [PATCH 03/35] x86/cpufeatures: Add CET CPU feature flags for Control-flow Enforcement Technology (CET)

[Kees Cook]

On Sun, Jan 30, 2022 at 01:18:06PM -0800, Rick Edgecombe wrote:
> From: Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx>
> 
> Add CPU feature flags 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

It looks like this only adds the SHSTK bit, maybe drop mention of IBT
here.

I wonder if we could land this (and the IBT part) without waiting for
everything else in the respective series?

-Kees

> 
> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx>
> Signed-off-by: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx>
> Cc: Kees Cook <keescook@xxxxxxxxxxxx>
> ---
> 
> v1:
>  - Remove IBT, can be added in a follow on IBT series.
> 
> Yu-cheng v25:
>  - Make X86_FEATURE_IBT depend on X86_FEATURE_SHSTK.
> 
> Yu-cheng v24:
>  - Update for splitting CONFIG_X86_CET to CONFIG_X86_SHADOW_STACK and
>    CONFIG_X86_IBT.
>  - Move DISABLE_IBT definition to the IBT series.
> 
>  arch/x86/include/asm/cpufeatures.h       | 1 +
>  arch/x86/include/asm/disabled-features.h | 8 +++++++-
>  arch/x86/kernel/cpu/cpuid-deps.c         | 1 +
>  3 files changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
> index 6db4e2932b3d..c3eb94b13fef 100644
> --- a/arch/x86/include/asm/cpufeatures.h
> +++ b/arch/x86/include/asm/cpufeatures.h
> @@ -355,6 +355,7 @@
>  #define X86_FEATURE_OSPKE		(16*32+ 4) /* OS Protection Keys Enable */
>  #define X86_FEATURE_WAITPKG		(16*32+ 5) /* UMONITOR/UMWAIT/TPAUSE Instructions */
>  #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/include/asm/disabled-features.h b/arch/x86/include/asm/disabled-features.h
> index 8f28fafa98b3..b7728f7afb2b 100644
> --- a/arch/x86/include/asm/disabled-features.h
> +++ b/arch/x86/include/asm/disabled-features.h
> @@ -65,6 +65,12 @@
>  # define DISABLE_SGX	(1 << (X86_FEATURE_SGX & 31))
>  #endif
>  
> +#ifdef CONFIG_X86_SHADOW_STACK
> +#define DISABLE_SHSTK	0
> +#else
> +#define DISABLE_SHSTK	(1 << (X86_FEATURE_SHSTK & 31))
> +#endif
> +
>  /*
>   * Make sure to add features to the correct mask
>   */
> @@ -85,7 +91,7 @@
>  #define DISABLED_MASK14	0
>  #define DISABLED_MASK15	0
>  #define DISABLED_MASK16	(DISABLE_PKU|DISABLE_OSPKE|DISABLE_LA57|DISABLE_UMIP| \
> -			 DISABLE_ENQCMD)
> +			 DISABLE_ENQCMD|DISABLE_SHSTK)
>  #define DISABLED_MASK17	0
>  #define DISABLED_MASK18	0
>  #define DISABLED_MASK19	0
> diff --git a/arch/x86/kernel/cpu/cpuid-deps.c b/arch/x86/kernel/cpu/cpuid-deps.c
> index c881bcafba7d..bf1b55a1ba21 100644
> --- a/arch/x86/kernel/cpu/cpuid-deps.c
> +++ b/arch/x86/kernel/cpu/cpuid-deps.c
> @@ -78,6 +78,7 @@ static const struct cpuid_dep cpuid_deps[] = {
>  	{ X86_FEATURE_XFD,			X86_FEATURE_XSAVES    },
>  	{ X86_FEATURE_XFD,			X86_FEATURE_XGETBV1   },
>  	{ X86_FEATURE_AMX_TILE,			X86_FEATURE_XFD       },
> +	{ X86_FEATURE_SHSTK,			X86_FEATURE_XSAVES    },
>  	{}
>  };
>  
> -- 
> 2.17.1
> 

-- 
Kees Cook