Re: [PATCH 6.1.y 2/2] arm64: Reset KASAN tag in copy_highpage with HW tags only

[Greg KH <gregkh@linuxfoundation.org>]

On Tue, Mar 07, 2023 at 09:49:25AM -0800, Peter Collingbourne wrote:
> During page migration, the copy_highpage function is used to copy the
> page data to the target page. If the source page is a userspace page
> with MTE tags, the KASAN tag of the target page must have the match-all
> tag in order to avoid tag check faults during subsequent accesses to the
> page by the kernel. However, the target page may have been allocated in
> a number of ways, some of which will use the KASAN allocator and will
> therefore end up setting the KASAN tag to a non-match-all tag. Therefore,
> update the target page's KASAN tag to match the source page.
> 
> We ended up unintentionally fixing this issue as a result of a bad
> merge conflict resolution between commit e059853d14ca ("arm64: mte:
> Fix/clarify the PG_mte_tagged semantics") and commit 20794545c146 ("arm64:
> kasan: Revert "arm64: mte: reset the page tag in page->flags""), which
> preserved a tag reset for PG_mte_tagged pages which was considered to be
> unnecessary at the time. Because SW tags KASAN uses separate tag storage,
> update the code to only reset the tags when HW tags KASAN is enabled.
> 
> Signed-off-by: Peter Collingbourne <pcc@google.com>
> Link: https://linux-review.googlesource.com/id/If303d8a709438d3ff5af5fd85706505830f52e0c
> Reported-by: "Kuan-Ying Lee (李冠穎)" <Kuan-Ying.Lee@mediatek.com>
> Cc: <stable@vger.kernel.org> # 6.1
> Fixes: 20794545c146 ("arm64: kasan: Revert "arm64: mte: reset the page tag in page->flags"")
> Reviewed-by: Andrey Konovalov <andreyknvl@gmail.com>
> Link: https://lore.kernel.org/r/20230215050911.1433132-1-pcc@google.com
> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
> (cherry picked from commit e74a68468062d7ebd8ce17069e12ccc64cc6a58c)
> ---
>  arch/arm64/mm/copypage.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 

Both now queued up, thanks.

greg k-h