Re: [PATCH v3 2/5] mm/hugetlb: use nth_page() in place of direct struct page manipulation.

[Zi Yan <ziy@nvidia.com>]

[-- Attachment #1: Type: text/plain, Size: 1303 bytes --]

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: 57a196a58421 ("hugetlb: simplify hugetlb handling in follow_page_mask")
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Zi Yan <ziy@nvidia.com>
> Reviewed-by: Muchun Song <songmuchun@bytedance.com>
> ---
>  mm/hugetlb.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index af74e83d92aa..8e68e6c53e66 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -6469,7 +6469,7 @@ struct page *hugetlb_follow_page_mask(struct vm_area_struct *vma,
>  			}
>  		}
>
> -		page += ((address & ~huge_page_mask(h)) >> PAGE_SHIFT);
> +		page = nth_page(page, ((address & ~huge_page_mask(h)) >> PAGE_SHIFT));
>
>  		/*
>  		 * Note that page may be a sub-page, and with vmemmap
> -- 
> 2.40.1

A wrong or non-existing page might be tried to be grabbed, either leading to
a non freeable page or kernel memory access errors. No bug is reported.
It comes from code inspection.


--
Best Regards,
Yan, Zi

[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 854 bytes --]