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

[Xianting Tian]

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@xxxxxxxxxxxxxxx
> > Reported-by: zjb194813@xxxxxxxxxxxxxxx
> > Reported-by: tianhu.hh@xxxxxxxxxxxxxxx
> > Signed-off-by: Xianting Tian <xianting.tian@xxxxxxxxxxxxxxxxx>
> > ---
> >   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@xxxxxxxxxx>
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@xxxxxxxxxxxxxxxxxx/
    Reported-and-tested-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
    Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
    Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>

> thanks,
>
> greg k-h