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

[Andrew Morton]

On Fri, 5 Dec 2025 02:09:06 +0100 Andrey Konovalov <andreyknvl@xxxxxxxxx> 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;
 	}
_