Re: [PATCH v3 1/5] mm/cma: use nth_page() in place of direct struct page manipulation.

Zi Yan
2023-09-14T02:17:10Z

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On 13 Sep 2023, at 16:12, Zi Yan wrote:

> From: Zi Yan <ziy@nvidia.com>
>
> When dealing with hugetlb pages, manipulating struct page pointers
> directly can get to wrong struct page, since struct page is not guaranteed
> to be contiguous on SPARSEMEM without VMEMMAP. Use nth_page() to handle
> it properly.
>
> Fixes: 2813b9c02962 ("kasan, mm, arm64: tag non slab memory allocated via pagealloc")
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Zi Yan <ziy@nvidia.com>
> Reviewed-by: Muchun Song <songmuchun@bytedance.com>
> ---
> mm/cma.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/cma.c b/mm/cma.c
> index da2967c6a223..2b2494fd6b59 100644
> --- a/mm/cma.c
> +++ b/mm/cma.c
> @@ -505,7 +505,7 @@ struct page *cma_alloc(struct cma *cma, unsigned long count,
> */
> if (page) {
> for (i = 0; i < count; i++)
> - page_kasan_tag_reset(page + i);
> + page_kasan_tag_reset(nth_page(page, i));
> }
>
> if (ret && !no_warn) {
> --
> 2.40.1

Without the fix, page_kasan_tag_reset() could reset wrong page tags, causing
a wrong kasan result. No related bug is reported. The fix comes from code
inspection.

--
Best Regards,
Yan, Zi

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