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

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Date:   Mon, 20 Jun 2022 12:17:22 +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 4.9] mm: page_alloc: validate buddy page before using

On Fri, Jun 17, 2022 at 04:25:35PM +0800, Xianting Tian wrote:
> 
> 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>
> 

All now queued up, thanks.

greg k-h