# Re: \[PATCH v8 01/12\] add support for Clang's Shadow Call Stack (SCS)

- From: Randy Dunlap \<rdunlap@infradead.org\>
- Date: 2020-02-19 04:20:05 
- List: linux-arm-kernel
- Page: https://ratatoskr.run/linux-arm-kernel/2020/02/5867068
- Thread: https://ratatoskr.run/linux-arm-kernel/2019/10/5749629/t/5.md

```text
Hi Sami,

a couple of minor tweaks:

On 2/18/20 4:08 PM, Sami Tolvanen wrote:
> diff --git a/arch/Kconfig b/arch/Kconfig
> index 98de654b79b3..66b34fd0df54 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -526,6 +526,40 @@ config STACKPROTECTOR_STRONG
>  	  about 20% of all kernel functions, which increases the kernel code
>  	  size by about 2%.
>  
> +config ARCH_SUPPORTS_SHADOW_CALL_STACK
> +	bool
> +	help
> +	  An architecture should select this if it supports Clang's Shadow
> +	  Call Stack, has asm/scs.h, and implements runtime support for shadow
> +	  stack switching.
> +
> +config SHADOW_CALL_STACK
> +	bool "Clang Shadow Call Stack"
> +	depends on ARCH_SUPPORTS_SHADOW_CALL_STACK
> +	help
> +	  This option enables Clang's Shadow Call Stack, which uses a
> +	  shadow stack to protect function return addresses from being
> +	  overwritten by an attacker. More information can be found from

	                                                      found in

> +	  Clang's documentation:
> +
> +	    https://clang.llvm.org/docs/ShadowCallStack.html
> +
> +	  Note that security guarantees in the kernel differ from the ones
> +	  documented for user space. The kernel must store addresses of shadow
> +	  stacks used by other tasks and interrupt handlers in memory, which
> +	  means an attacker capable reading and writing arbitrary memory may

	                    capable of

> +	  be able to locate them and hijack control flow by modifying shadow
> +	  stacks that are not currently in use.
> +
> +config SHADOW_CALL_STACK_VMAP
> +	bool "Use virtually mapped shadow call stacks"
> +	depends on SHADOW_CALL_STACK
> +	help
> +	  Use virtually mapped shadow call stacks. Selecting this option
> +	  provides better stack exhaustion protection, but increases per-thread
> +	  memory consumption as a full page is allocated for each shadow stack.
> +
> +
>  config HAVE_ARCH_WITHIN_STACK_FRAMES
>  	bool
>  	help


thanks.
-- 
~Randy


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