Re: [PATCH v3 08/12] kasan/um: select ARCH_DEFER_KASAN and call kasan_init_generic

[Andrey Ryabinin <ryabinin.a.a@gmail.com>]

On 7/17/25 4:27 PM, Sabyrzhan Tasbolatov wrote:
> UserMode Linux needs deferred KASAN initialization as it has a custom
> kasan_arch_is_ready() implementation that tracks shadow memory readiness
> via the kasan_um_is_ready flag.
> 
> Select ARCH_DEFER_KASAN to enable the unified static key mechanism
> for runtime KASAN control. Call kasan_init_generic() which handles
> Generic KASAN initialization and enables the static key.
> 
> Delete the key kasan_um_is_ready in favor of the unified kasan_enabled()
> interface.
> 
> Note that kasan_init_generic has __init macro, which is called by
> kasan_init() which is not marked with __init in arch/um code.
> 
> Closes: https://bugzilla.kernel.org/show_bug.cgi?id=217049
> Signed-off-by: Sabyrzhan Tasbolatov <snovitoll@gmail.com>
> ---
> Changes in v3:
> - Added CONFIG_ARCH_DEFER_KASAN selection for proper runtime control
> ---
>  arch/um/Kconfig             | 1 +
>  arch/um/include/asm/kasan.h | 5 -----
>  arch/um/kernel/mem.c        | 4 ++--
>  3 files changed, 3 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/um/Kconfig b/arch/um/Kconfig
> index f08e8a7fac9..fd6d78bba52 100644
> --- a/arch/um/Kconfig
> +++ b/arch/um/Kconfig
> @@ -8,6 +8,7 @@ config UML
>  	select ARCH_WANTS_DYNAMIC_TASK_STRUCT
>  	select ARCH_HAS_CPU_FINALIZE_INIT
>  	select ARCH_HAS_FORTIFY_SOURCE
> +	select ARCH_DEFER_KASAN
>  	select ARCH_HAS_GCOV_PROFILE_ALL
>  	select ARCH_HAS_KCOV
>  	select ARCH_HAS_STRNCPY_FROM_USER
> diff --git a/arch/um/include/asm/kasan.h b/arch/um/include/asm/kasan.h
> index f97bb1f7b85..81bcdc0f962 100644
> --- a/arch/um/include/asm/kasan.h
> +++ b/arch/um/include/asm/kasan.h
> @@ -24,11 +24,6 @@
>  
>  #ifdef CONFIG_KASAN
>  void kasan_init(void);
> -extern int kasan_um_is_ready;
> -
> -#ifdef CONFIG_STATIC_LINK
> -#define kasan_arch_is_ready() (kasan_um_is_ready)
> -#endif
>  #else
>  static inline void kasan_init(void) { }
>  #endif /* CONFIG_KASAN */
> diff --git a/arch/um/kernel/mem.c b/arch/um/kernel/mem.c
> index 76bec7de81b..058cb70e330 100644
> --- a/arch/um/kernel/mem.c
> +++ b/arch/um/kernel/mem.c
> @@ -21,9 +21,9 @@
>  #include <os.h>
>  #include <um_malloc.h>
>  #include <linux/sched/task.h>
> +#include <linux/kasan.h>
>  
>  #ifdef CONFIG_KASAN
> -int kasan_um_is_ready;
>  void kasan_init(void)
>  {
>  	/*
> @@ -32,7 +32,7 @@ void kasan_init(void)
>  	 */
>  	kasan_map_memory((void *)KASAN_SHADOW_START, KASAN_SHADOW_SIZE);
>  	init_task.kasan_depth = 0;
> -	kasan_um_is_ready = true;
> +	kasan_init_generic();

I think this runs before jump_label_init(), and static keys shouldn't be switched before that.>  }
>  
>  static void (*kasan_init_ptr)(void)