linux-kernel - Re: [PATCH 4/4] mm/kasan: make kasan=on|off take effect for all three modes

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Message-ID: <9ca2790c-1214-47a0-abdc-212ee3ea5e18@lucifer.local>
Date: Wed, 6 Aug 2025 17:26:11 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: SeongJae Park <sj@...nel.org>
Cc: Baoquan He <bhe@...hat.com>, linux-mm@...ck.org, ryabinin.a.a@...il.com,
        glider@...gle.com, andreyknvl@...il.com, dvyukov@...gle.com,
        vincenzo.frascino@....com, akpm@...ux-foundation.org,
        kasan-dev@...glegroups.com, linux-kernel@...r.kernel.org,
        kexec@...ts.infradead.org
Subject: Re: [PATCH 4/4] mm/kasan: make kasan=on|off take effect for all
 three modes

On Tue, Aug 05, 2025 at 10:22:31PM -0700, SeongJae Park wrote:
> Hello Baoqua,
>
> On Tue,  5 Aug 2025 14:23:33 +0800 Baoquan He <bhe@...hat.com> wrote:
>
> > Now everything is ready, set kasan=off can disable kasan for all
> > three modes.
> >
> > Signed-off-by: Baoquan He <bhe@...hat.com>
> > ---
> >  include/linux/kasan-enabled.h | 11 +----------
> >  1 file changed, 1 insertion(+), 10 deletions(-)
> >
> > diff --git a/include/linux/kasan-enabled.h b/include/linux/kasan-enabled.h
> > index 32f2d19f599f..b5857e15ef14 100644
> > --- a/include/linux/kasan-enabled.h
> > +++ b/include/linux/kasan-enabled.h
> > @@ -8,30 +8,21 @@ extern bool kasan_arg_disabled;
> >
> >  DECLARE_STATIC_KEY_FALSE(kasan_flag_enabled);
> >
> > -#ifdef CONFIG_KASAN_HW_TAGS
> > -
> >  static __always_inline bool kasan_enabled(void)
> >  {
> >  	return static_branch_likely(&kasan_flag_enabled);
> >  }
>
> I found mm-new build fails when CONFIG_KASAN is unset as below, and 'git
> bisect' points this patch.

Yup just hit this + bisected here.

>
>       LD      .tmp_vmlinux1
>     ld: lib/stackdepot.o:(__jump_table+0x8): undefined reference to `kasan_flag_enabled'
>
> Since kasna_flag_enabled is defined in mm/kasan/common.c, I confirmed diff like
> below fixes this.  I think it may not be a correct fix though, since I didn't
> read this patchset thoroughly.
>
> diff --git a/include/linux/kasan-enabled.h b/include/linux/kasan-enabled.h
> index b5857e15ef14..a53d112b1020 100644
> --- a/include/linux/kasan-enabled.h
> +++ b/include/linux/kasan-enabled.h
> @@ -8,11 +8,22 @@ extern bool kasan_arg_disabled;
>
>  DECLARE_STATIC_KEY_FALSE(kasan_flag_enabled);
>
> +#ifdef CONFIG_KASAN
> +

Shouldn't we put this above the static key declaration?

Feels like the whole header should be included really.

>  static __always_inline bool kasan_enabled(void)
>  {
>  	return static_branch_likely(&kasan_flag_enabled);
>  }
>
> +#else /* CONFIG_KASAN */
> +
> +static inline bool kasan_enabled(void)
> +{
> +	return false;
> +}
> +
> +#endif
> +
>  #ifdef CONFIG_KASAN_HW_TAGS
>  static inline bool kasan_hw_tags_enabled(void)
>  {
>
>
> [...]
>
> Thanks,
> SJ
>

Cheers, Lorenzo