Re: [PATCH 1/8] arm64: Enable VMAP_STACK support

[Mark Rutland <mark.rutland@arm.com>]

Hi Breno,

On Mon, Jul 07, 2025 at 09:01:01AM -0700, Breno Leitao wrote:
> Enable virtually mapped kernel stacks for ARM64. This provides better
> stack overflow detection and improved security by mapping kernel stacks
> in vmalloc space rather than using direct mapping.
> 
> VMAP_STACK helps catch stack overflows early by placing guard pages
> around kernel stacks, and also provides better isolation between
> kernel stacks and other kernel data structures.
> 
> All dependencies are satisfied for arm64: HAVE_ARCH_VMAP_STACK is
> already selected above, and KASAN_VMALLOC is selected when KASAN is
> enabled, meeting the KASAN dependency requirements.

I reckon it might be better to say something like:

| arm64: Mandate VMAP_STACK
|
| On arm64, VMAP_STACK has been enabled by default for a while now, and
| the only reason to disable it was a historical lack of support for
| KASAN_VMALLOC. Today there's no good reason to disable VMAP_STACK.
|
| Mandate VMAP_STACK, which will allow code to be simplified in
| subsequent patches.

... to make it clear that we're not changing the default, and we are
removing the ability to deselect VMAP_STACK.

Either way, the patch itself looks good to me.

Mark.

> 
> Suggested-by: Will Deacon <will@kernel.org>
> Signed-off-by: Breno Leitao <leitao@debian.org>
> ---
>  arch/arm64/Kconfig | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 393d71124f5d..179b302f43c2 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -280,6 +280,7 @@ config ARM64
>  	select HAVE_SOFTIRQ_ON_OWN_STACK
>  	select USER_STACKTRACE_SUPPORT
>  	select VDSO_GETRANDOM
> +	select VMAP_STACK
>  	help
>  	  ARM 64-bit (AArch64) Linux support.
>  
> 
> -- 
> 2.47.1
>