Re: [PATCH v4 01/12] mm/kasan: add conditional checks in functions to return directly if kasan is disabled

[Andrey Konovalov <andreyknvl@gmail.com>]

On Fri, Nov 28, 2025 at 4:33 AM Baoquan He <bhe@redhat.com> wrote:
>
> The current codes only check if kasan is disabled for hw_tags
> mode. Here add the conditional checks for functional functions of
> generic mode and sw_tags mode.
>
> This is prepared for later adding kernel parameter kasan=on|off for
> all three kasan modes.
>
> Signed-off-by: Baoquan He <bhe@redhat.com>
> ---
>  mm/kasan/generic.c    | 17 +++++++++++++++--
>  mm/kasan/init.c       |  6 ++++++
>  mm/kasan/quarantine.c |  3 +++
>  mm/kasan/report.c     |  4 +++-
>  mm/kasan/shadow.c     | 11 ++++++++++-
>  mm/kasan/sw_tags.c    |  3 +++
>  6 files changed, 40 insertions(+), 4 deletions(-)
>
> diff --git a/mm/kasan/generic.c b/mm/kasan/generic.c
> index 2b8e73f5f6a7..aff822aa2bd6 100644
> --- a/mm/kasan/generic.c
> +++ b/mm/kasan/generic.c
> @@ -214,12 +214,13 @@ bool kasan_byte_accessible(const void *addr)
>
>  void kasan_cache_shrink(struct kmem_cache *cache)
>  {
> -       kasan_quarantine_remove_cache(cache);
> +       if (kasan_enabled())

Please move these checks to include/linux/kasan.h and add __helpers to
consistent with how it's done for other KASAN annotation calls.
Otherwise eventually these checks start creeping into lower level
functions and the logic of checking when and whether KASAN is enabled
becomes a mess.



> +               kasan_quarantine_remove_cache(cache);
>  }
>
>  void kasan_cache_shutdown(struct kmem_cache *cache)
>  {
> -       if (!__kmem_cache_empty(cache))
> +       if (kasan_enabled() && !__kmem_cache_empty(cache))
>                 kasan_quarantine_remove_cache(cache);
>  }
>
> @@ -239,6 +240,9 @@ void __asan_register_globals(void *ptr, ssize_t size)
>         int i;
>         struct kasan_global *globals = ptr;
>
> +       if (!kasan_enabled())
> +               return;
> +
>         for (i = 0; i < size; i++)
>                 register_global(&globals[i]);
>  }
> @@ -369,6 +373,9 @@ void kasan_cache_create(struct kmem_cache *cache, unsigned int *size,
>         unsigned int rem_free_meta_size;
>         unsigned int orig_alloc_meta_offset;
>
> +       if (!kasan_enabled())
> +               return;
> +
>         if (!kasan_requires_meta())
>                 return;
>
> @@ -518,6 +525,9 @@ size_t kasan_metadata_size(struct kmem_cache *cache, bool in_object)
>  {
>         struct kasan_cache *info = &cache->kasan_info;
>
> +       if (!kasan_enabled())
> +               return 0;
> +
>         if (!kasan_requires_meta())
>                 return 0;
>
> @@ -543,6 +553,9 @@ void kasan_record_aux_stack(void *addr)
>         struct kasan_alloc_meta *alloc_meta;
>         void *object;
>
> +       if (!kasan_enabled())
> +               return;
> +
>         if (is_kfence_address(addr) || !slab)
>                 return;
>
> diff --git a/mm/kasan/init.c b/mm/kasan/init.c
> index f084e7a5df1e..c78d77ed47bc 100644
> --- a/mm/kasan/init.c
> +++ b/mm/kasan/init.c
> @@ -447,6 +447,9 @@ void kasan_remove_zero_shadow(void *start, unsigned long size)
>         unsigned long addr, end, next;
>         pgd_t *pgd;
>
> +       if (!kasan_enabled())
> +               return;
> +
>         addr = (unsigned long)kasan_mem_to_shadow(start);
>         end = addr + (size >> KASAN_SHADOW_SCALE_SHIFT);
>
> @@ -482,6 +485,9 @@ int kasan_add_zero_shadow(void *start, unsigned long size)
>         int ret;
>         void *shadow_start, *shadow_end;
>
> +       if (!kasan_enabled())
> +               return 0;
> +
>         shadow_start = kasan_mem_to_shadow(start);
>         shadow_end = shadow_start + (size >> KASAN_SHADOW_SCALE_SHIFT);
>
> diff --git a/mm/kasan/quarantine.c b/mm/kasan/quarantine.c
> index 6958aa713c67..a6dc2c3d8a15 100644
> --- a/mm/kasan/quarantine.c
> +++ b/mm/kasan/quarantine.c
> @@ -405,6 +405,9 @@ static int __init kasan_cpu_quarantine_init(void)
>  {
>         int ret = 0;
>
> +       if (!kasan_enabled())
> +               return 0;
> +
>         ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "mm/kasan:online",
>                                 kasan_cpu_online, kasan_cpu_offline);
>         if (ret < 0)
> diff --git a/mm/kasan/report.c b/mm/kasan/report.c
> index 62c01b4527eb..884357fa74ed 100644
> --- a/mm/kasan/report.c
> +++ b/mm/kasan/report.c
> @@ -576,7 +576,9 @@ bool kasan_report(const void *addr, size_t size, bool is_write,
>         unsigned long irq_flags;
>         struct kasan_report_info info;
>
> -       if (unlikely(report_suppressed_sw()) || unlikely(!report_enabled())) {
> +       if (unlikely(report_suppressed_sw()) ||
> +           unlikely(!report_enabled()) ||
> +           !kasan_enabled()) {
>                 ret = false;
>                 goto out;
>         }
> diff --git a/mm/kasan/shadow.c b/mm/kasan/shadow.c
> index 29a751a8a08d..f73a691421de 100644
> --- a/mm/kasan/shadow.c
> +++ b/mm/kasan/shadow.c
> @@ -164,6 +164,8 @@ void kasan_unpoison(const void *addr, size_t size, bool init)
>  {
>         u8 tag = get_tag(addr);
>
> +       if (!kasan_enabled())
> +               return;
>         /*
>          * Perform shadow offset calculation based on untagged address, as
>          * some of the callers (e.g. kasan_unpoison_new_object) pass tagged
> @@ -277,7 +279,8 @@ static int __meminit kasan_mem_notifier(struct notifier_block *nb,
>
>  static int __init kasan_memhotplug_init(void)
>  {
> -       hotplug_memory_notifier(kasan_mem_notifier, DEFAULT_CALLBACK_PRI);
> +       if (kasan_enabled())
> +               hotplug_memory_notifier(kasan_mem_notifier, DEFAULT_CALLBACK_PRI);
>
>         return 0;
>  }
> @@ -658,6 +661,9 @@ int kasan_alloc_module_shadow(void *addr, size_t size, gfp_t gfp_mask)
>         size_t shadow_size;
>         unsigned long shadow_start;
>
> +       if (!kasan_enabled())
> +               return 0;
> +
>         shadow_start = (unsigned long)kasan_mem_to_shadow(addr);
>         scaled_size = (size + KASAN_GRANULE_SIZE - 1) >>
>                                 KASAN_SHADOW_SCALE_SHIFT;
> @@ -694,6 +700,9 @@ int kasan_alloc_module_shadow(void *addr, size_t size, gfp_t gfp_mask)
>
>  void kasan_free_module_shadow(const struct vm_struct *vm)
>  {
> +       if (!kasan_enabled())
> +               return;
> +
>         if (IS_ENABLED(CONFIG_UML))
>                 return;
>
> diff --git a/mm/kasan/sw_tags.c b/mm/kasan/sw_tags.c
> index c75741a74602..6c1caec4261a 100644
> --- a/mm/kasan/sw_tags.c
> +++ b/mm/kasan/sw_tags.c
> @@ -79,6 +79,9 @@ bool kasan_check_range(const void *addr, size_t size, bool write,
>         u8 *shadow_first, *shadow_last, *shadow;
>         void *untagged_addr;
>
> +       if (!kasan_enabled())
> +               return true;
> +
>         if (unlikely(size == 0))
>                 return true;
>
> --
> 2.41.0
>