linux-kernel - Re: [PATCH v4 02/12] mm/kasan: move kasan= code to common place

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Message-ID: <CA+fCnZeHZ4+8GOn0untumM0TE9TeSHqja9kAsbEb-+jbEFNQQQ@mail.gmail.com>
Date: Thu, 4 Dec 2025 17:39:10 +0100
From: Andrey Konovalov <andreyknvl@...il.com>
To: Baoquan He <bhe@...hat.com>
Cc: linux-mm@...ck.org, ryabinin.a.a@...il.com, glider@...gle.com, 
	dvyukov@...gle.com, vincenzo.frascino@....com, akpm@...ux-foundation.org, 
	kasan-dev@...glegroups.com, linux-kernel@...r.kernel.org, 
	kexec@...ts.infradead.org, elver@...gle.com, sj@...nel.org, 
	lorenzo.stoakes@...cle.com, snovitoll@...il.com, christophe.leroy@...roup.eu
Subject: Re: [PATCH v4 02/12] mm/kasan: move kasan= code to common place

On Fri, Nov 28, 2025 at 4:33 AM Baoquan He <bhe@...hat.com> wrote:
>
> This allows generic and sw_tags to be set in kernel cmdline too.
>
> When at it, rename 'kasan_arg' to 'kasan_arg_disabled' as a bool
> variable. And expose 'kasan_flag_enabled' to kasan common place
> too.

This asks to be two separate patches.

>
> This is prepared for later adding kernel parameter kasan=on|off for
> all three kasan modes.
>
> Signed-off-by: Baoquan He <bhe@...hat.com>
> ---
>  include/linux/kasan-enabled.h |  4 +++-
>  mm/kasan/common.c             | 20 ++++++++++++++++++--
>  mm/kasan/hw_tags.c            | 28 ++--------------------------
>  3 files changed, 23 insertions(+), 29 deletions(-)
>
> diff --git a/include/linux/kasan-enabled.h b/include/linux/kasan-enabled.h
> index 9eca967d8526..b05ec6329fbe 100644
> --- a/include/linux/kasan-enabled.h
> +++ b/include/linux/kasan-enabled.h
> @@ -4,13 +4,15 @@
>
>  #include <linux/static_key.h>
>
> -#if defined(CONFIG_ARCH_DEFER_KASAN) || defined(CONFIG_KASAN_HW_TAGS)

These changes of moving/removing CONFIG_ARCH_DEFER_KASAN also seem to
belong to a separate patch (or should be combined with patch 12?); the
commit message does not even mention them.

> +extern bool kasan_arg_disabled;
> +
>  /*
>   * Global runtime flag for KASAN modes that need runtime control.
>   * Used by ARCH_DEFER_KASAN architectures and HW_TAGS mode.
>   */
>  DECLARE_STATIC_KEY_FALSE(kasan_flag_enabled);

So kasan_flag_enabled is now always exposed here...

>
> +#if defined(CONFIG_ARCH_DEFER_KASAN) || defined(CONFIG_KASAN_HW_TAGS)

but the functions that use it are not. Why?


>  /*
>   * Runtime control for shadow memory initialization or HW_TAGS mode.
>   * Uses static key for architectures that need deferred KASAN or HW_TAGS.
> diff --git a/mm/kasan/common.c b/mm/kasan/common.c
> index 1d27f1bd260b..ac14956986ee 100644
> --- a/mm/kasan/common.c
> +++ b/mm/kasan/common.c
> @@ -32,14 +32,30 @@
>  #include "kasan.h"
>  #include "../slab.h"
>
> -#if defined(CONFIG_ARCH_DEFER_KASAN) || defined(CONFIG_KASAN_HW_TAGS)
>  /*
>   * Definition of the unified static key declared in kasan-enabled.h.
>   * This provides consistent runtime enable/disable across KASAN modes.
>   */
>  DEFINE_STATIC_KEY_FALSE(kasan_flag_enabled);
>  EXPORT_SYMBOL_GPL(kasan_flag_enabled);
> -#endif
> +
> +bool kasan_arg_disabled __ro_after_init;
> +/* kasan=off/on */
> +static int __init early_kasan_flag(char *arg)
> +{
> +       if (!arg)
> +               return -EINVAL;
> +
> +       if (!strcmp(arg, "off"))
> +               kasan_arg_disabled = true;
> +       else if (!strcmp(arg, "on"))
> +               kasan_arg_disabled = false;
> +       else
> +               return -EINVAL;
> +
> +       return 0;
> +}
> +early_param("kasan", early_kasan_flag);
>
>  struct slab *kasan_addr_to_slab(const void *addr)
>  {
> diff --git a/mm/kasan/hw_tags.c b/mm/kasan/hw_tags.c
> index 1c373cc4b3fa..709c91abc1b1 100644
> --- a/mm/kasan/hw_tags.c
> +++ b/mm/kasan/hw_tags.c
> @@ -22,12 +22,6 @@
>
>  #include "kasan.h"
>
> -enum kasan_arg {
> -       KASAN_ARG_DEFAULT,
> -       KASAN_ARG_OFF,
> -       KASAN_ARG_ON,
> -};
> -
>  enum kasan_arg_mode {
>         KASAN_ARG_MODE_DEFAULT,
>         KASAN_ARG_MODE_SYNC,
> @@ -41,7 +35,6 @@ enum kasan_arg_vmalloc {
>         KASAN_ARG_VMALLOC_ON,
>  };
>
> -static enum kasan_arg kasan_arg __ro_after_init;
>  static enum kasan_arg_mode kasan_arg_mode __ro_after_init;
>  static enum kasan_arg_vmalloc kasan_arg_vmalloc __initdata;
>
> @@ -81,23 +74,6 @@ unsigned int kasan_page_alloc_sample_order = PAGE_ALLOC_SAMPLE_ORDER_DEFAULT;
>
>  DEFINE_PER_CPU(long, kasan_page_alloc_skip);
>
> -/* kasan=off/on */
> -static int __init early_kasan_flag(char *arg)
> -{
> -       if (!arg)
> -               return -EINVAL;
> -
> -       if (!strcmp(arg, "off"))
> -               kasan_arg = KASAN_ARG_OFF;
> -       else if (!strcmp(arg, "on"))
> -               kasan_arg = KASAN_ARG_ON;
> -       else
> -               return -EINVAL;
> -
> -       return 0;
> -}
> -early_param("kasan", early_kasan_flag);
> -
>  /* kasan.mode=sync/async/asymm */
>  static int __init early_kasan_mode(char *arg)
>  {
> @@ -222,7 +198,7 @@ void kasan_init_hw_tags_cpu(void)
>          * When this function is called, kasan_flag_enabled is not yet
>          * set by kasan_init_hw_tags(). Thus, check kasan_arg instead.
>          */
> -       if (kasan_arg == KASAN_ARG_OFF)
> +       if (kasan_arg_disabled)
>                 return;
>
>         /*
> @@ -240,7 +216,7 @@ void __init kasan_init_hw_tags(void)
>                 return;
>
>         /* If KASAN is disabled via command line, don't initialize it. */
> -       if (kasan_arg == KASAN_ARG_OFF)
> +       if (kasan_arg_disabled)
>                 return;
>
>         switch (kasan_arg_mode) {
> --
> 2.41.0
>