linux-kernel - Re: [PATCH 4.9] mm: page_alloc: validate buddy page before using

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Date:   Fri, 17 Jun 2022 16:25:35 +0800
From:   Xianting Tian <xianting.tian@...ux.alibaba.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     akpm@...ux-foundation.org, ziy@...dia.com, stable@...r.kernel.org,
        guoren@...nel.org, huanyi.xj@...baba-inc.com, guohanjun@...wei.com,
        zjb194813@...baba-inc.com, tianhu.hh@...baba-inc.com,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4.9] mm: page_alloc: validate buddy page before using


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@...r.kernel.org
>> Reported-by: zjb194813@...baba-inc.com
>> Reported-by: tianhu.hh@...baba-inc.com
>> Signed-off-by: Xianting Tian <xianting.tian@...ux.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@...dia.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@...dmis.org>
     Signed-off-by: Zi Yan <ziy@...dia.com>
     Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>

>
> thanks,
>
> greg k-h