On Mon, Aug 25, 2025 at 10:31 PM Maciej Wieczor-Retman
<maciej.wieczor-retman@xxxxxxxxx> wrote:
>
> The problem presented here is related to NUMA systems and tag-based
> KASAN mode. It can be explained in the following points:
>
> 1. There can be more than one virtual memory chunk.
> 2. Chunk's base address has a tag.
> 3. The base address points at the first chunk and thus inherits
> the tag of the first chunk.
> 4. The subsequent chunks will be accessed with the tag from the
> first chunk.
> 5. Thus, the subsequent chunks need to have their tag set to
> match that of the first chunk.
>
> Unpoison all vms[]->addr memory and pointers with the same tag to
> resolve the mismatch.
>
> Signed-off-by: Maciej Wieczor-Retman <maciej.wieczor-retman@xxxxxxxxx>
> ---
> Changelog v4:
> - Move tagging the vms[]->addr to this new patch and leave refactoring
> there.
> - Comment the fix to provide some context.
>
> mm/kasan/shadow.c | 10 +++++++++-
> 1 file changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/mm/kasan/shadow.c b/mm/kasan/shadow.c
> index b41f74d68916..ee2488371784 100644
> --- a/mm/kasan/shadow.c
> +++ b/mm/kasan/shadow.c
> @@ -646,13 +646,21 @@ void __kasan_poison_vmalloc(const void *start, unsigned long size)
> kasan_poison(start, size, KASAN_VMALLOC_INVALID, false);
> }
>
> +/*
> + * A tag mismatch happens when calculating per-cpu chunk addresses, because
> + * they all inherit the tag from vms[0]->addr, even when nr_vms is bigger
> + * than 1. This is a problem because all the vms[]->addr come from separate
> + * allocations and have different tags so while the calculated address is
> + * correct the tag isn't.
> + */
> void __kasan_unpoison_vmap_areas(struct vm_struct **vms, int nr_vms)
> {
> int area;
>
> for (area = 0 ; area < nr_vms ; area++) {
> kasan_poison(vms[area]->addr, vms[area]->size,
> - arch_kasan_get_tag(vms[area]->addr), false);
> + arch_kasan_get_tag(vms[0]->addr), false);
> + arch_kasan_set_tag(vms[area]->addr, arch_kasan_get_tag(vms[0]->addr));
> }
> }
>
> --
> 2.50.1
>
Do we need this fix for the HW_TAGS mode too?
