Re: [PATCH 06/11] mm: Introduce ARCH_HAS_KERNEL_SHADOW_STACK

From: Mike Rapoport <rppt@kernel.org>
To: Deepak Gupta <debug@rivosinc.com>
Cc: Paul Walmsley <paul.walmsley@sifive.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	Alexandre Ghiti <alex@ghiti.fr>,
	Masahiro Yamada <masahiroy@kernel.org>,
	Nathan Chancellor <nathan@kernel.org>,
	Nicolas Schier <nicolas.schier@linux.dev>,
	Andrew Morton <akpm@linux-foundation.org>,
	David Hildenbrand <david@redhat.com>,
	Lorenzo Stoakes <lorenzo.stoakes@oracle.com>,
	"Liam R. Howlett" <Liam.Howlett@oracle.com>,
	Vlastimil Babka <vbabka@suse.cz>,
	Suren Baghdasaryan <surenb@google.com>,
	Michal Hocko <mhocko@suse.com>,
	Nick Desaulniers <nick.desaulniers+lkml@gmail.com>,
	Bill Wendling <morbo@google.com>,
	Monk Chiang <monk.chiang@sifive.com>,
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	Justin Stitt <justinstitt@google.com>,
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	ved@rivosinc.com
Subject: Re: [PATCH 06/11] mm: Introduce ARCH_HAS_KERNEL_SHADOW_STACK
Date: Sat, 26 Jul 2025 10:42:02 +0300	[thread overview]
Message-ID: <aISGypOAaDGaUZgd@kernel.org> (raw)
In-Reply-To: <20250724-riscv_kcfi-v1-6-04b8fa44c98c@rivosinc.com>

On Thu, Jul 24, 2025 at 04:36:59PM -0700, Deepak Gupta wrote:
> commit bcc9d04e74 ("mm: Introduce ARCH_HAS_USER_SHADOW_STACK") introduced
> `ARCH_HAS_USER_SHADOW_STACK`. Introducing `ARCH_HAS_KERNEL_SHADOW_STACK`
> so that arches can enable hardware assistance for kernel shadow stack.
> 
> If `CONFIG_DYNAMIC_SCS` or `CONFIG_ARCH_HAS_KERNEL_SHADOW_STACK` are
> selected, skip compiler flag `-fsanitizer=shadow-call-stack`.
> 
> Signed-off-by: Deepak Gupta <debug@rivosinc.com>
> ---
>  Makefile   | 2 +-
>  mm/Kconfig | 6 ++++++
>  2 files changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/Makefile b/Makefile
> index 35e6e5240c61..7e3ecca9353d 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -987,7 +987,7 @@ LDFLAGS_vmlinux += --gc-sections
>  endif
>  
>  ifdef CONFIG_SHADOW_CALL_STACK
> -ifndef CONFIG_DYNAMIC_SCS
> +ifeq ($(or $(CONFIG_DYNAMIC_SCS),$(CONFIG_ARCH_HAS_KERNEL_SHADOW_STACK)),false)
>  CC_FLAGS_SCS	:= -fsanitize=shadow-call-stack
>  KBUILD_CFLAGS	+= $(CC_FLAGS_SCS)
>  KBUILD_RUSTFLAGS += -Zsanitizer=shadow-call-stack
> diff --git a/mm/Kconfig b/mm/Kconfig
> index 781be3240e21..f295ea611cdb 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -1367,6 +1367,12 @@ config ARCH_HAS_USER_SHADOW_STACK
>  	  The architecture has hardware support for userspace shadow call
>            stacks (eg, x86 CET, arm64 GCS or RISC-V Zicfiss).
>  
> +config ARCH_HAS_KERNEL_SHADOW_STACK
> +	bool
> +	help
> +	  The architecture has hardware support for kernel shadow call
> +          stacks (eg, x86 CET, arm64 GCS or RISC-V Zicfiss).

nit: tab and two space for indentation of the help text

> +

I think both ARCH_HAS_USER_SHADOW_STACK and ARCH_HAS_KERNEL_SHADOW_STACK
belong to arch/Kconfig rather than mm/Kconfig

>  config ARCH_SUPPORTS_PT_RECLAIM
>  	def_bool n
>  
> 
> -- 
> 2.43.0
> 

-- 
Sincerely yours,
Mike.