2022-06-16 16:26:05

by Xianting Tian

[permalink] [raw]
Subject: [PATCH 4.9] mm: page_alloc: validate buddy page before using

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: [email protected]
Reported-by: [email protected]
Reported-by: [email protected]
Signed-off-by: Xianting Tian <[email protected]>
---
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


2022-06-17 08:38:04

by Xianting Tian

[permalink] [raw]
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: [email protected]
>> Reported-by: [email protected]
>> Reported-by: [email protected]
>> Signed-off-by: Xianting Tian <[email protected]>
>> ---
>> 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 <[email protected]>
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/[email protected]/
    Reported-and-tested-by: Steven Rostedt <[email protected]>
    Signed-off-by: Zi Yan <[email protected]>
    Signed-off-by: Linus Torvalds <[email protected]>

>
> thanks,
>
> greg k-h

2022-06-17 08:38:04

by Greg Kroah-Hartman

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

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: [email protected]
> Reported-by: [email protected]
> Reported-by: [email protected]
> Signed-off-by: Xianting Tian <[email protected]>
> ---
> 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?

thanks,

greg k-h

2022-06-20 10:23:38

by Greg Kroah-Hartman

[permalink] [raw]
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: [email protected]
> > > Reported-by: [email protected]
> > > Reported-by: [email protected]
> > > Signed-off-by: Xianting Tian <[email protected]>
> > > ---
> > > 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 <[email protected]>
> 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/[email protected]/
>     Reported-and-tested-by: Steven Rostedt <[email protected]>
>     Signed-off-by: Zi Yan <[email protected]>
>     Signed-off-by: Linus Torvalds <[email protected]>
>

All now queued up, thanks.

greg k-h