Re: [PATCH v4 5/9] kasan/loongarch: select ARCH_DEFER_KASAN and call kasan_init_generic

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

On 8/5/25 4:26 PM, Sabyrzhan Tasbolatov wrote:
> LoongArch needs deferred KASAN initialization as it has a custom
> kasan_arch_is_ready() implementation that tracks shadow memory
> readiness via the kasan_early_stage 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.
> 
> Replace kasan_arch_is_ready() with kasan_enabled() and delete the
> flag kasan_early_stage in favor of the unified kasan_enabled()
> interface.
> 
> Note that init_task.kasan_depth = 0 is called after kasan_init_generic(),
> which is different than in other arch kasan_init(). This is left
> unchanged as it cannot be tested.
> 
> Closes: https://bugzilla.kernel.org/show_bug.cgi?id=217049
> Signed-off-by: Sabyrzhan Tasbolatov <snovitoll@gmail.com>
> ---
> Changes in v4:
> - Replaced !kasan_enabled() with !kasan_shadow_initialized() in
>   loongarch which selects ARCH_DEFER_KASAN (Andrey Ryabinin)
> ---
>  arch/loongarch/Kconfig             | 1 +
>  arch/loongarch/include/asm/kasan.h | 7 -------
>  arch/loongarch/mm/kasan_init.c     | 8 ++------
>  3 files changed, 3 insertions(+), 13 deletions(-)
> 
> diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
> index f0abc38c40a..f6304c073ec 100644
> --- a/arch/loongarch/Kconfig
> +++ b/arch/loongarch/Kconfig
> @@ -9,6 +9,7 @@ config LOONGARCH
>  	select ACPI_PPTT if ACPI
>  	select ACPI_SYSTEM_POWER_STATES_SUPPORT	if ACPI
>  	select ARCH_BINFMT_ELF_STATE
> +	select ARCH_DEFER_KASAN
>  	select ARCH_DISABLE_KASAN_INLINE
>  	select ARCH_ENABLE_MEMORY_HOTPLUG
>  	select ARCH_ENABLE_MEMORY_HOTREMOVE
> diff --git a/arch/loongarch/include/asm/kasan.h b/arch/loongarch/include/asm/kasan.h
> index 62f139a9c87..0e50e5b5e05 100644
> --- a/arch/loongarch/include/asm/kasan.h
> +++ b/arch/loongarch/include/asm/kasan.h
> @@ -66,7 +66,6 @@
>  #define XKPRANGE_WC_SHADOW_OFFSET	(KASAN_SHADOW_START + XKPRANGE_WC_KASAN_OFFSET)
>  #define XKVRANGE_VC_SHADOW_OFFSET	(KASAN_SHADOW_START + XKVRANGE_VC_KASAN_OFFSET)
>  
> -extern bool kasan_early_stage;
>  extern unsigned char kasan_early_shadow_page[PAGE_SIZE];
>  
>  #define kasan_mem_to_shadow kasan_mem_to_shadow
> @@ -75,12 +74,6 @@ void *kasan_mem_to_shadow(const void *addr);
>  #define kasan_shadow_to_mem kasan_shadow_to_mem
>  const void *kasan_shadow_to_mem(const void *shadow_addr);
>  
> -#define kasan_arch_is_ready kasan_arch_is_ready
> -static __always_inline bool kasan_arch_is_ready(void)
> -{
> -	return !kasan_early_stage;
> -}
> -
>  #define addr_has_metadata addr_has_metadata
>  static __always_inline bool addr_has_metadata(const void *addr)
>  {
> diff --git a/arch/loongarch/mm/kasan_init.c b/arch/loongarch/mm/kasan_init.c
> index d2681272d8f..57fb6e98376 100644
> --- a/arch/loongarch/mm/kasan_init.c
> +++ b/arch/loongarch/mm/kasan_init.c
> @@ -40,11 +40,9 @@ static pgd_t kasan_pg_dir[PTRS_PER_PGD] __initdata __aligned(PAGE_SIZE);
>  #define __pte_none(early, pte) (early ? pte_none(pte) : \
>  ((pte_val(pte) & _PFN_MASK) == (unsigned long)__pa(kasan_early_shadow_page)))
>  
> -bool kasan_early_stage = true;
> -
>  void *kasan_mem_to_shadow(const void *addr)
>  {
> -	if (!kasan_arch_is_ready()) {
> +	if (!kasan_shadow_initialized()) {
>  		return (void *)(kasan_early_shadow_page);
>  	} else {
>  		unsigned long maddr = (unsigned long)addr;
> @@ -298,8 +296,6 @@ void __init kasan_init(void)
>  	kasan_populate_early_shadow(kasan_mem_to_shadow((void *)VMALLOC_START),
>  					kasan_mem_to_shadow((void *)KFENCE_AREA_END));
>  
> -	kasan_early_stage = false;
> -

There is a reason for this line to be here.
Your patch will change the result of the follow up kasan_mem_to_shadow() call and
feed the wrong address to kasan_map_populate()


>  	/* Populate the linear mapping */
>  	for_each_mem_range(i, &pa_start, &pa_end) {
>  		void *start = (void *)phys_to_virt(pa_start);
> @@ -329,5 +325,5 @@ void __init kasan_init(void)
>  
>  	/* At this point kasan is fully initialized. Enable error messages */
>  	init_task.kasan_depth = 0;
> -	pr_info("KernelAddressSanitizer initialized.\n");
> +	kasan_init_generic();
>  }