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

["Maciej Wieczór-Retman" <m.wieczorretman@pm.me>]

Thanks for checking the patches out, do you want me to send v4 with this
correction or is it redundant now that Andrew already wrote it?

Kind regards
Maciej Wieczór-Retman

On 2025-12-05 at 04:38:27 +0100, Andrey Konovalov wrote:
>On Fri, Dec 5, 2025 at 4:22 AM Andrew Morton <akpm@linux-foundation.org> wrote:
>>
>> On Fri, 5 Dec 2025 02:09:06 +0100 Andrey Konovalov <andreyknvl@gmail.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!