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Subject: Re: [PATCH 4.9] mm: page_alloc: validate buddy page before using
To:     Greg KH <gregkh@linuxfoundation.org>
Cc:     akpm@linux-foundation.org, ziy@nvidia.com, stable@vger.kernel.org,
        guoren@kernel.org, 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: <20220616161928.3565294-1-xianting.tian@linux.alibaba.com>
 <Yqw5ZPyeMemfeKKY@kroah.com>
From:   Xianting Tian <xianting.tian@linux.alibaba.com>
Message-ID: <c091b3a2-394a-59b4-dd98-98774e33afea@linux.alibaba.com>
Date:   Fri, 17 Jun 2022 16:25:35 +0800
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在 2022/6/17 下午4:20, Greg KH 写道:
> On Fri, Jun 17, 2022 at 12:19:28AM +0800, Xianting Tian wrote:
>> 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
>> -- 
>> 2.17.1
>>
> What is the git commit id of this change in Linus's tree?

It is this one,

commit 787af64d05cd528aac9ad16752d11bb1c6061bb9
Author: Zi Yan <ziy@nvidia.com>
Date:   Wed Mar 30 15:45:43 2022 -0700

     mm: page_alloc: validate buddy before check its migratetype.

     Whenever a buddy page is found, page_is_buddy() should be called to
     check its validity.  Add the missing check during pageblock merge 
check.

     Fixes: 1dd214b8f21c ("mm: page_alloc: avoid merging 
non-fallbackable pageblocks with others")
     Link: 
https://lore.kernel.org/all/20220330154208.71aca532@gandalf.local.home/
     Reported-and-tested-by: Steven Rostedt <rostedt@goodmis.org>
     Signed-off-by: Zi Yan <ziy@nvidia.com>
     Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

>
> thanks,
>
> greg k-h