linux-kernel - Re: [PATCH 5.15] mm: validate buddy page before using

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Message-ID: <2E1BD795-A6EA-4272-859B-A29DFAF6DC07@nvidia.com>
Date:   Mon, 20 Jun 2022 08:25:33 -0400
From:   Zi Yan <ziy@...dia.com>
To:     Xianting Tian <xianting.tian@...ux.alibaba.com>
Cc:     Greg KH <gregkh@...uxfoundation.org>, akpm@...ux-foundation.org,
        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 5.15] mm: validate buddy page before using

On 20 Jun 2022, at 8:18, Xianting Tian wrote:

> 在 2022/6/20 下午8:06, Greg KH 写道:
>> On Mon, Jun 20, 2022 at 07:57:05PM +0800, Xianting Tian wrote:
>>> 在 2022/6/20 下午7:42, Greg KH 写道:
>>>> On Mon, Jun 20, 2022 at 06:54:44PM +0800, Xianting Tian wrote:
>>>>> 在 2022/6/20 下午6:17, Greg KH 写道:
>>>>>> On Fri, Jun 17, 2022 at 12:17:45AM +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 unset_migratetype_isolate(), we also need the fix, so move page_is_buddy()
>>>>>>> from mm/page_alloc.c to mm/internal.h
>>>>>>>
>>>>>>> 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/internal.h       | 34 ++++++++++++++++++++++++++++++++++
>>>>>>>     mm/page_alloc.c     | 37 +++----------------------------------
>>>>>>>     mm/page_isolation.c |  3 ++-
>>>>>>>     3 files changed, 39 insertions(+), 35 deletions(-)
>>>>>> What is the commit id of this in Linus's tree?
>>>>> It is also 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>
>>>> This commit looks nothing like what you posted here.
>>>>
>>>> Why the vast difference with no explaination as to why these are so
>>>> different from the other backports you provided here?  Also why is the
>>>> subject lines changed?
>>> Yes, the changes of 5.15 are not same with others branches, because we need
>>> additional fix for 5.15,
>>>
>>> You can check it in the thread:
>>>
>>> https://lore.kernel.org/linux-mm/435B45C3-E6A5-43B2-A5A2-318C748691FC@nvidia.com/ <https://lore.kernel.org/linux-mm/435B45C3-E6A5-43B2-A5A2-318C748691FC@nvidia.com/>
>>>
>>> Right. But pfn_valid_within() was removed since 5.15. So your fix is
>>> required for kernels between 5.15 and 5.17 (inclusive).
>> What is "your fix" here?
>>
>> This change differs a lot from what is in Linus's tree now, so this all
>> needs to be resend and fixed up as I mention above if we are going to be
>> able to take this.  As-is, it's all not correct so are dropped.
>
> I think, for branches except 5.15,  you can just backport Zi Yan's commit 787af64d05cd in Linus tree. I won't send more patches further,

Please do not back port my commit 787af64d05cd directly, because although
it fixes the issue, the code indentation is not right. At least, I tried
to cherry-pick the commit and failed. The commit just happens to fix
the issue in commit d9dddbf55667.

>
> For 5.15, because it need additional fix except commit 787af64d05cd,  I will send a new patch as your comments.
>
> Is it ok for you?
>
>>
>> thanks,
>>
>> greg k-h

--
Best Regards,
Yan, Zi

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