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

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Message-ID: <aJtBJgC82CpUkwTi@MiWiFi-R3L-srv>
Date: Tue, 12 Aug 2025 21:27:02 +0800
From: Baoquan He <bhe@...hat.com>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Cc: SeongJae Park <sj@...nel.org>, 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 08/08/25 at 02:24pm, Lorenzo Stoakes wrote:
> On Fri, Aug 08, 2025 at 09:08:35PM +0800, Baoquan He wrote:
> > On 08/06/25 at 05:26pm, Lorenzo Stoakes wrote:
......
> > > > 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.
> >
> > You are right, kasan_flag_enabled should be included in CONFIG_KASAN
> > ifdeffery scope.
> 
> Firstly I _LOVE_ the term 'ifdeffery scope'. Fantastic :)

Learned from upstream people with expertise on both english and kernel, :-)

> 
> >
> > Since CONFIG_KASAN_HW_TAGS depends on CONFIG_KASAN, we may not need
> > include below CONFIG_KASAN_HW_TAGS ifdeffery into CONFIG_KASAN ifdeffery
> > scope. Not sure if this is incorrect.
> 
> Well I don't think CONFIG_KASAN_HW_TAGS is necessarily implied right? So these
> should remain I think, just nested in CONFIG_KASAN, should be fine.

After investigation, I keep the CONFIG_KASAN_HW_TAGS ifdeffery scope out
of CONFIG_KASAN scope. Otherwise, I need define the dummy
kasan_hw_tags_enabled() function twice. I am personally not fan of the
style. While if that is preferred in kernel, I can change it.

#ifdef CONFIG_KASAN

#ifdef CONFIG_KASAN_HW_TAGS
......
#ifdef CONFIG_KASAN_HW_TAGS
static inline bool kasan_hw_tags_enabled(void)
{
        return kasan_enabled();
}
#else /* CONFIG_KASAN_HW_TAGS */
static inline bool kasan_hw_tags_enabled(void)
{
        return false;
}
#endif /* CONFIG_KASAN_HW_TAGS */
.....
#else /* CONFIG_KASAN */
static inline bool kasan_hw_tags_enabled(void)
{
        return false;
}
#endif