* [PATCH v1] mm/hugetlb: fix refs calculation from unaligned @vaddr
@ 2021-07-13 15:24 Joao Martins
2021-07-13 20:29 ` Mike Kravetz
0 siblings, 1 reply; 4+ messages in thread
From: Joao Martins @ 2021-07-13 15:24 UTC (permalink / raw)
To: linux-mm; +Cc: Mike Kravetz, Andrew Morton, Joao Martins
commit 82e5d378b0e47 ("mm/hugetlb: refactor subpage recording")
refactored the count of subpages but missed an edge case when @vaddr is
not aligned to PAGE_SIZE e.g. when close to vma->vm_end. It would then
errousnly set @refs to 0 and record_subpages_vmas() wouldn't set the
@pages array element to its value, consequently causing the reported
null-deref by syzbot.
Fix it by aligning down @vaddr by PAGE_SIZE in @refs calculation.
Reported-by: syzbot+a3fcd59df1b372066f5a@syzkaller.appspotmail.com
Fixes: 82e5d378b0e47 ("mm/hugetlb: refactor subpage recording")
Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
---
An alternate approach is to have record_subpages_vmas() iterate while
addr < vm_end and renaming @refs to nr_pages (which would limit how many
pages we should store). But I felt that this approach would be slightly
more convoluted?
Side-Note: I could add a WARN_ON_ONCE(!refs) and/or create an
helper like vma_pages() but with a ulong addr argument e.g.
vma_pages_from(vma, vaddr).
The syzbot repro no longer reproduces after this patch. Additionally, ran
the libhugetlbfs tests (which were passing without this), gup_test and an
extra gup_test extension that take an offset to exercise gup() starting
address not being page aligned.
---
mm/hugetlb.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 924553aa8f78..dfc940d5221d 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -5440,8 +5440,9 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
continue;
}
- refs = min3(pages_per_huge_page(h) - pfn_offset,
- (vma->vm_end - vaddr) >> PAGE_SHIFT, remainder);
+ /* vaddr may not be aligned to PAGE_SIZE */
+ refs = min3(pages_per_huge_page(h) - pfn_offset, remainder,
+ (vma->vm_end - ALIGN_DOWN(vaddr, PAGE_SIZE)) >> PAGE_SHIFT);
if (pages || vmas)
record_subpages_vmas(mem_map_offset(page, pfn_offset),
--
2.17.1
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH v1] mm/hugetlb: fix refs calculation from unaligned @vaddr
2021-07-13 15:24 [PATCH v1] mm/hugetlb: fix refs calculation from unaligned @vaddr Joao Martins
@ 2021-07-13 20:29 ` Mike Kravetz
2021-07-14 1:02 ` Andrew Morton
2021-07-14 9:54 ` Joao Martins
0 siblings, 2 replies; 4+ messages in thread
From: Mike Kravetz @ 2021-07-13 20:29 UTC (permalink / raw)
To: Joao Martins, linux-mm; +Cc: Andrew Morton
On 7/13/21 8:24 AM, Joao Martins wrote:
> commit 82e5d378b0e47 ("mm/hugetlb: refactor subpage recording")
> refactored the count of subpages but missed an edge case when @vaddr is
> not aligned to PAGE_SIZE e.g. when close to vma->vm_end. It would then
> errousnly set @refs to 0 and record_subpages_vmas() wouldn't set the
> @pages array element to its value, consequently causing the reported
> null-deref by syzbot.
>
> Fix it by aligning down @vaddr by PAGE_SIZE in @refs calculation.
Thanks for finding and fixing!
>
> Reported-by: syzbot+a3fcd59df1b372066f5a@syzkaller.appspotmail.com
> Fixes: 82e5d378b0e47 ("mm/hugetlb: refactor subpage recording")
> Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
> ---
> An alternate approach is to have record_subpages_vmas() iterate while
> addr < vm_end and renaming @refs to nr_pages (which would limit how many
> pages we should store). But I felt that this approach would be slightly
> more convoluted?
I prefer the approach you have taken in this patch.
>
> Side-Note: I could add a WARN_ON_ONCE(!refs) and/or create an
> helper like vma_pages() but with a ulong addr argument e.g.
> vma_pages_from(vma, vaddr).
IIUC, the only way refs could be zero is if there was error in
caluclations within this routine. Correct?
IMO, the only reason to add a warning would be if there are any assumptions
based on things outside this routine which could cause refs to be zero.
> The syzbot repro no longer reproduces after this patch. Additionally, ran
> the libhugetlbfs tests (which were passing without this), gup_test and an
> extra gup_test extension that take an offset to exercise gup() starting
> address not being page aligned.
> ---
> mm/hugetlb.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 924553aa8f78..dfc940d5221d 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -5440,8 +5440,9 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
> continue;
> }
>
> - refs = min3(pages_per_huge_page(h) - pfn_offset,
> - (vma->vm_end - vaddr) >> PAGE_SHIFT, remainder);
> + /* vaddr may not be aligned to PAGE_SIZE */
> + refs = min3(pages_per_huge_page(h) - pfn_offset, remainder,
> + (vma->vm_end - ALIGN_DOWN(vaddr, PAGE_SIZE)) >> PAGE_SHIFT);
>
> if (pages || vmas)
> record_subpages_vmas(mem_map_offset(page, pfn_offset),
>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
--
Mike Kravetz
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH v1] mm/hugetlb: fix refs calculation from unaligned @vaddr
2021-07-13 20:29 ` Mike Kravetz
@ 2021-07-14 1:02 ` Andrew Morton
2021-07-14 9:54 ` Joao Martins
1 sibling, 0 replies; 4+ messages in thread
From: Andrew Morton @ 2021-07-14 1:02 UTC (permalink / raw)
To: Mike Kravetz; +Cc: Joao Martins, linux-mm
On Tue, 13 Jul 2021 13:29:20 -0700 Mike Kravetz <mike.kravetz@oracle.com> wrote:
> On 7/13/21 8:24 AM, Joao Martins wrote:
>
> > The syzbot repro no longer reproduces after this patch. Additionally, ran
> > the libhugetlbfs tests (which were passing without this), gup_test and an
> > extra gup_test extension that take an offset to exercise gup() starting
> > address not being page aligned.
> > ---
> > mm/hugetlb.c | 5 +++--
> > 1 file changed, 3 insertions(+), 2 deletions(-)
> >
> > diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> > index 924553aa8f78..dfc940d5221d 100644
> > --- a/mm/hugetlb.c
> > +++ b/mm/hugetlb.c
> > @@ -5440,8 +5440,9 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
> > continue;
> > }
> >
> > - refs = min3(pages_per_huge_page(h) - pfn_offset,
> > - (vma->vm_end - vaddr) >> PAGE_SHIFT, remainder);
> > + /* vaddr may not be aligned to PAGE_SIZE */
> > + refs = min3(pages_per_huge_page(h) - pfn_offset, remainder,
> > + (vma->vm_end - ALIGN_DOWN(vaddr, PAGE_SIZE)) >> PAGE_SHIFT);
> >
> > if (pages || vmas)
> > record_subpages_vmas(mem_map_offset(page, pfn_offset),
> >
>
> Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
I'll add cc:stable to this.
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH v1] mm/hugetlb: fix refs calculation from unaligned @vaddr
2021-07-13 20:29 ` Mike Kravetz
2021-07-14 1:02 ` Andrew Morton
@ 2021-07-14 9:54 ` Joao Martins
1 sibling, 0 replies; 4+ messages in thread
From: Joao Martins @ 2021-07-14 9:54 UTC (permalink / raw)
To: Mike Kravetz; +Cc: Andrew Morton, linux-mm
On 7/13/21 9:29 PM, Mike Kravetz wrote:
> On 7/13/21 8:24 AM, Joao Martins wrote:
>> commit 82e5d378b0e47 ("mm/hugetlb: refactor subpage recording")
>> refactored the count of subpages but missed an edge case when @vaddr is
>> not aligned to PAGE_SIZE e.g. when close to vma->vm_end. It would then
>> errousnly set @refs to 0 and record_subpages_vmas() wouldn't set the
>> @pages array element to its value, consequently causing the reported
>> null-deref by syzbot.
>>
>> Fix it by aligning down @vaddr by PAGE_SIZE in @refs calculation.
>
> Thanks for finding and fixing!
>
>>
>> Reported-by: syzbot+a3fcd59df1b372066f5a@syzkaller.appspotmail.com
>> Fixes: 82e5d378b0e47 ("mm/hugetlb: refactor subpage recording")
>> Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
>> ---
>> An alternate approach is to have record_subpages_vmas() iterate while
>> addr < vm_end and renaming @refs to nr_pages (which would limit how many
>> pages we should store). But I felt that this approach would be slightly
>> more convoluted?
>
> I prefer the approach you have taken in this patch.
>
OK.
>>
>> Side-Note: I could add a WARN_ON_ONCE(!refs) and/or create an
>> helper like vma_pages() but with a ulong addr argument e.g.
>> vma_pages_from(vma, vaddr).
>
> IIUC, the only way refs could be zero is if there was error in
> caluclations within this routine. Correct?
Right. Albeit vaddr initialization is originally set with gup() starting address.
> IMO, the only reason to add a warning would be if there are any assumptions
> based on things outside this routine which could cause refs to be zero.
>
/me nods
>> The syzbot repro no longer reproduces after this patch. Additionally, ran
>> the libhugetlbfs tests (which were passing without this), gup_test and an
>> extra gup_test extension that take an offset to exercise gup() starting
>> address not being page aligned.
>> ---
>> mm/hugetlb.c | 5 +++--
>> 1 file changed, 3 insertions(+), 2 deletions(-)
>>
>> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
>> index 924553aa8f78..dfc940d5221d 100644
>> --- a/mm/hugetlb.c
>> +++ b/mm/hugetlb.c
>> @@ -5440,8 +5440,9 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
>> continue;
>> }
>>
>> - refs = min3(pages_per_huge_page(h) - pfn_offset,
>> - (vma->vm_end - vaddr) >> PAGE_SHIFT, remainder);
>> + /* vaddr may not be aligned to PAGE_SIZE */
>> + refs = min3(pages_per_huge_page(h) - pfn_offset, remainder,
>> + (vma->vm_end - ALIGN_DOWN(vaddr, PAGE_SIZE)) >> PAGE_SHIFT);
>>
>> if (pages || vmas)
>> record_subpages_vmas(mem_map_offset(page, pfn_offset),
>>
>
> Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
>
Thanks!
^ permalink raw reply [flat|nested] 4+ messages in thread
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2021-07-13 15:24 [PATCH v1] mm/hugetlb: fix refs calculation from unaligned @vaddr Joao Martins
2021-07-13 20:29 ` Mike Kravetz
2021-07-14 1:02 ` Andrew Morton
2021-07-14 9:54 ` Joao Martins
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