linux-kernel - Re: [PATCH v3 3/3] kasan: Unpoison vms[area] addresses with a common tag

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Message-ID: <CA+fCnZfBqNKAkwKmdu7YAPWjPDWY=wRkUiWuYjEzK4_tNhSGFA@mail.gmail.com>
Date: Fri, 5 Dec 2025 04:38:27 +0100
From: Andrey Konovalov <andreyknvl@...il.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Maciej Wieczor-Retman <m.wieczorretman@...me>, Andrey Ryabinin <ryabinin.a.a@...il.com>, 
	Alexander Potapenko <glider@...gle.com>, Dmitry Vyukov <dvyukov@...gle.com>, 
	Vincenzo Frascino <vincenzo.frascino@....com>, Marco Elver <elver@...gle.com>, jiayuan.chen@...ux.dev, 
	stable@...r.kernel.org, 
	Maciej Wieczor-Retman <maciej.wieczor-retman@...el.com>, kasan-dev@...glegroups.com, 
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 3/3] kasan: Unpoison vms[area] addresses with a common tag

On Fri, Dec 5, 2025 at 4:22 AM Andrew Morton <akpm@...ux-foundation.org> wrote:
>
> On Fri, 5 Dec 2025 02:09:06 +0100 Andrey Konovalov <andreyknvl@...il.com> wrote:
>
> > > --- a/mm/kasan/common.c
> > > +++ b/mm/kasan/common.c
> > > @@ -591,11 +591,28 @@ void __kasan_unpoison_vmap_areas(struct vm_struct **vms, int nr_vms,
> > >         unsigned long size;
> > >         void *addr;
> > >         int area;
> > > +       u8 tag;
> > > +
> > > +       /*
> > > +        * If KASAN_VMALLOC_KEEP_TAG was set at this point, all vms[] pointers
> > > +        * would be unpoisoned with the KASAN_TAG_KERNEL which would disable
> > > +        * KASAN checks down the line.
> > > +        */
> > > +       if (flags & KASAN_VMALLOC_KEEP_TAG) {
> >
> > I think we can do a WARN_ON() here: passing KASAN_VMALLOC_KEEP_TAG to
> > this function would be a bug in KASAN annotations and thus a kernel
> > bug. Therefore, printing a WARNING seems justified.
>
> This?
>
> --- a/mm/kasan/common.c~kasan-unpoison-vms-addresses-with-a-common-tag-fix
> +++ a/mm/kasan/common.c
> @@ -598,7 +598,7 @@ void __kasan_unpoison_vmap_areas(struct
>          * would be unpoisoned with the KASAN_TAG_KERNEL which would disable
>          * KASAN checks down the line.
>          */
> -       if (flags & KASAN_VMALLOC_KEEP_TAG) {
> +       if (WARN_ON_ONCE(flags & KASAN_VMALLOC_KEEP_TAG)) {
>                 pr_warn("KASAN_VMALLOC_KEEP_TAG flag shouldn't be already set!\n");
>                 return;
>         }
> _
>

Can also drop pr_warn(), but this is fine too. Thanks!