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Subject: Re: [PATCH] mm: page_alloc: validate buddy page before using
To:     akpm@linux-foundation.org, ziy@nvidia.com,
        gregkh@linuxfoundation.org, stable@vger.kernel.org,
        guoren@kernel.org
Cc:     huanyi.xj@alibaba-inc.com, guohanjun@huawei.com,
        zjb194813@alibaba-inc.com, tianhu.hh@alibaba-inc.com,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org
References: <20220616161746.3565225-1-xianting.tian@linux.alibaba.com>
From:   Xianting Tian <xianting.tian@linux.alibaba.com>
Message-ID: <b08725b1-2f4b-cea0-43fc-1ce0a2a7e8f4@linux.alibaba.com>
Date:   Fri, 17 Jun 2022 00:20:19 +0800
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Sorry, please ignore this one.

?? 2022/6/17 ????12:17, Xianting Tian д??:
> Commit 787af64d05cd ("mm: page_alloc: validate buddy before check its migratetype.")
> fixes a bug in 1dd214b8f21c and there is a similar bug in d9dddbf55667 that
> can be fixed in a similar way too.
>
> In addition, for RISC-V arch the first 2MB RAM could be reserved for opensbi,
> so it would have pfn_base=512 and mem_map began with 512th PFN when
> CONFIG_FLATMEM=y.
> But __find_buddy_pfn algorithm thinks the start pfn 0, it could get 0 pfn or
> less than the pfn_base value. We need page_is_buddy() to verify the buddy to
> prevent accessing an invalid buddy.
>
> Fixes: d9dddbf55667 ("mm/page_alloc: prevent merging between isolated and other pageblocks")
> Cc: stable@vger.kernel.org
> Reported-by: zjb194813@alibaba-inc.com
> Reported-by: tianhu.hh@alibaba-inc.com
> Signed-off-by: Xianting Tian <xianting.tian@linux.alibaba.com>
> ---
>   mm/page_alloc.c | 3 +++
>   1 file changed, 3 insertions(+)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index a6e682569e5b..1c423faa4b62 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -864,6 +864,9 @@ static inline void __free_one_page(struct page *page,
>   
>   			buddy_idx = __find_buddy_index(page_idx, order);
>   			buddy = page + (buddy_idx - page_idx);
> +
> +			if (!page_is_buddy(page, buddy, order))
> +				goto done_merging;
>   			buddy_mt = get_pageblock_migratetype(buddy);
>   
>   			if (migratetype != buddy_mt