Re: [PATCH v2 02/39] x86/cet/shstk: Add Kconfig option for Shadow Stack

[Kirill A . Shutemov]

On Thu, Sep 29, 2022 at 03:28:59PM -0700, Rick Edgecombe wrote:
> From: Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx>
> 
> Shadow Stack provides protection against function return address
> corruption. It is active when the processor supports it, the kernel has
> CONFIG_X86_SHADOW_STACK enabled, and the application is built for the
> feature. This is only implemented for the 64-bit kernel. When it is
> enabled, legacy non-Shadow Stack applications continue to work, but without
> protection.
> 
> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx>
> Co-developed-by: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx>
> Signed-off-by: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx>
> Cc: Kees Cook <keescook@xxxxxxxxxxxx>
> 
> ---
> 
> v2:
>  - Remove already wrong kernel size increase info (tlgx)
>  - Change prompt to remove "Intel" (tglx)
>  - Update line about what CPUs are supported (Dave)
> 
> Yu-cheng v25:
>  - Remove X86_CET and use X86_SHADOW_STACK directly.
> 
> Yu-cheng v24:
>  - Update for the splitting X86_CET to X86_SHADOW_STACK and X86_IBT.
> 
>  arch/x86/Kconfig           | 18 ++++++++++++++++++
>  arch/x86/Kconfig.assembler |  5 +++++
>  2 files changed, 23 insertions(+)
> 
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index f9920f1341c8..b68eb75887b8 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -26,6 +26,7 @@ config X86_64
>  	depends on 64BIT
>  	# Options that are inherently 64-bit kernel only:
>  	select ARCH_HAS_GIGANTIC_PAGE
> +	select ARCH_HAS_SHADOW_STACK
>  	select ARCH_SUPPORTS_INT128 if CC_HAS_INT128
>  	select ARCH_USE_CMPXCHG_LOCKREF
>  	select HAVE_ARCH_SOFT_DIRTY
> @@ -1936,6 +1937,23 @@ config X86_SGX
>  
>  	  If unsure, say N.
>  
> +config ARCH_HAS_SHADOW_STACK
> +	def_bool n

Hm. Shouldn't ARCH_HAS_SHADOW_STACK definition be in arch/Kconfig, not
under arch/x86?

Also, I think "def_bool n" has the same meaning as just "bool", no?

> +
> +config X86_SHADOW_STACK
> +	prompt "X86 Shadow Stack"
> +	def_bool n

Maybe just

	bool "X86 Shadow Stack"

?

> +	depends on ARCH_HAS_SHADOW_STACK
> +	select ARCH_USES_HIGH_VMA_FLAGS
> +	help
> +	  Shadow Stack protection is a hardware feature that detects function
> +	  return address corruption. Today the kernel's support is limited to
> +	  virtualizing it in KVM guests.
> +
> +	  CPUs supporting shadow stacks were first released in 2020.
> +
> +	  If unsure, say N.
> +
>  config EFI
>  	bool "EFI runtime service support"
>  	depends on ACPI
> diff --git a/arch/x86/Kconfig.assembler b/arch/x86/Kconfig.assembler
> index 26b8c08e2fc4..00c79dd93651 100644
> --- a/arch/x86/Kconfig.assembler
> +++ b/arch/x86/Kconfig.assembler
> @@ -19,3 +19,8 @@ config AS_TPAUSE
>  	def_bool $(as-instr,tpause %ecx)
>  	help
>  	  Supported by binutils >= 2.31.1 and LLVM integrated assembler >= V7
> +
> +config AS_WRUSS
> +	def_bool $(as-instr,wrussq %rax$(comma)(%rbx))
> +	help
> +	  Supported by binutils >= 2.31 and LLVM integrated assembler
> -- 
> 2.17.1
> 

-- 
  Kiryl Shutsemau / Kirill A. Shutemov