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

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Date:   Mon, 20 Jun 2022 14:24:51 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Xianting Tian <xianting.tian@...ux.alibaba.com>
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 5.15] mm: validate buddy page before using

On Mon, Jun 20, 2022 at 08:18:40PM +0800, 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,

So just for 5.18?  I am confused.

> 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?

No, please send fixed up patches for all branches you want them applied
to as I do not understand what to do here at all, sorry.

greg k-h