[PATCH v3 01/12] lib/kasan: introduce CONFIG_ARCH_DEFER_KASAN option

[Andrey Ryabinin]

On 7/17/25 4:27 PM, Sabyrzhan Tasbolatov wrote:
> Introduce CONFIG_ARCH_DEFER_KASAN to identify architectures that need
> to defer KASAN initialization until shadow memory is properly set up.
> 
> Some architectures (like PowerPC with radix MMU) need to set up their
> shadow memory mappings before KASAN can be safely enabled, while others
> (like s390, x86, arm) can enable KASAN much earlier or even from the
> beginning.
> 
> This option allows us to:
> 1. Use static keys only where needed (avoiding overhead)
> 2. Use compile-time constants for arch that don't need runtime checks
> 3. Maintain optimal performance for both scenarios
> 
> Architectures that need deferred KASAN should select this option.
> Architectures that can enable KASAN early will get compile-time
> optimizations instead of runtime checks.
> 
> Closes: https://bugzilla.kernel.org/show_bug.cgi?id=217049
> Signed-off-by: Sabyrzhan Tasbolatov <snovitoll at gmail.com>
> ---
> Changes in v3:
> - Introduced CONFIG_ARCH_DEFER_KASAN to control static key usage
> ---
>  lib/Kconfig.kasan | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/lib/Kconfig.kasan b/lib/Kconfig.kasan
> index f82889a830f..38456560c85 100644
> --- a/lib/Kconfig.kasan
> +++ b/lib/Kconfig.kasan
> @@ -19,6 +19,14 @@ config ARCH_DISABLE_KASAN_INLINE
>  	  Disables both inline and stack instrumentation. Selected by
>  	  architectures that do not support these instrumentation types.
>  
> +config ARCH_DEFER_KASAN
> +	bool
> +	help
> +	  Architectures should select this if they need to defer KASAN
> +	  initialization until shadow memory is properly set up. This
> +	  enables runtime control via static keys. Otherwise, KASAN uses
> +	  compile-time constants for better performance.
> +
>  config CC_HAS_KASAN_GENERIC
>  	def_bool $(cc-option, -fsanitize=kernel-address)
>  

This needs to be merged with the next patch where this option at least has some users.