| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-ID: <696e5cdb-5292-c5fb-43f4-32c91ae82607@126.com>
Date: Thu, 31 Oct 2019 20:32:01 +0800
From: Li Xinhai <lixinhai_lxh@....com>
To: Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
Li Xinhai <lixinhai.lxh@...il.com>
Cc: "linux-mm@...ck.org" <linux-mm@...ck.org>,
akpm <akpm@...ux-foundation.org>,
Vlastimil Babka <vbabka@...e.cz>,
Michal Hocko <mhocko@...nel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Linux API <linux-api@...r.kernel.org>,
Hugh Dickins <hughd@...gle.com>
Subject: Re: [PATCH v2] mm: Fix checking unmapped holes for mbind
On 2019/10/31 17:06, Naoya Horiguchi wrote:
> On Thu, Oct 31, 2019 at 11:15:09AM +0800, Li Xinhai wrote:
>> On 2019-10-29 at 17:56 Li Xinhai wrote:
>>> queue_pages_range() will check for unmapped holes besides queue pages for
>>> migration. The rules for checking unmapped holes are:
>>> 1 Unmapped holes at any part of the specified range should be reported as
>>> EFAULT if mbind() for none MPOL_DEFAULT cases;
>>> 2 Unmapped holes at any part of the specified range should be ignored if
>>> mbind() for MPOL_DEFAULT case;
>>> Note that the second rule is the current implementation, but it seems
>>> conflicts the Linux API definition.
>>>
>>> queue_pages_test_walk() is fixed by introduce new fields in struct
>>> queue_pages which help to check:
>>> 1 holes at head and tail side of specified range;
>>> 2 the whole range is in a hole;
>>>
>>> Besides, queue_pages_test_walk() must update previous vma record no matter
>>> the current vma should be considered for queue pages or not.
>>>
>>
>> More details about current issue (which breaks the mbind() API definition):
>> 1. In queue_pages_test_walk()
>> checking on (!vma->vm_next && vma->vm_end < end) would never success,
>> because 'end' passed from walk_page_test() make sure "end <= vma->vm_end". so hole
>> beyond the last vma can't be detected.
>>
>> 2. queue_pages_test_walk() only called for vma, and 'start', 'end' parameters are guaranteed
>> within vma. Then, if the range starting or ending in an unmapped hole,
>> queue_pages_test_walk() don't have chance to be called to check. In other words, the
>> current code can detect this case (range span over hole):
>> [ vma ][ hole ][ vma]
>> [ range ]
>> but cant not detect these case :
>> [ vma ][ hole ][ vma]
>> [ range ]
>> [ vma ][ hole ][ vma ]
>> [ range ]
>
> IIRC, page table walker (walk_page_range()) should be designed to
> handle these range inputs by separating into sub-ranges by vma
> boundaries like below (with your notation):
>
> [ vma ][ hole ][ vma ]
> [ ][ ][ ] // for your 1st case
> [ ][ ] // for your 2nd case
> [ ][ ] // for your 3rd case
>
Yes, pagewalk works exactly as your description.
> And I found that .pte_hole is undefined in queue_pages_walk_ops.
> So I'm guessing now that that's why hole regions are ignored and
> the definition of EFAULT behavior in manpage is violated.
> So providing proper .pte_hole callback could be another approach
> for this issue which might fit better to the design.
Using the .pte_hole() can be one option, we may stop detecting the
unmapped holes when .pte_hole() been first called for a hole which
is outside vma. But, .pte_hole() would be called many times during
the walking, because it is called for holes inside and outside VMA.
.test_walk() is called once for one vma, and not called for other
situation, so better for cost.
> IOW, queue_pages_test_walk() might not the right place to handle
> hole regions by definition.
I guess the original design was to avoid walking those vma twice, one
for test holes and one for queue pages. Maybe we can find better
choice?
>
> Thanks,
> Naoya Horiguchi
>
>>
>> 3. a checking in mbind_range() try to recover if the hole is in head side, but can't
>> recover if hole is in tail side of range.
>>
>> - Xinhai
>>
>>> Fixes: 9d8cebd4bcd7 ("mm: fix mbind vma merge problem")
>>> Fixes: 6f4576e3687b ("mempolicy: apply page table walker on queue_pages_range()")
>>> Fixes: 48684a65b4e3 ("mm: pagewalk: fix misbehavior of walk_page_range for vma(VM_PFNMAP)")
>>> Signed-off-by: Li Xinhai <lixinhai.li@...il.com>
>>> ---
>>> Changes in v2:
>>> - Fix the unmapped holes checking in queue_pages_test_walk() instead of
>>> mbind_rnage().
>>>
>>> mm/mempolicy.c | 44 +++++++++++++++++++++++++++++---------------
>>> 1 file changed, 29 insertions(+), 15 deletions(-)
>>>
>>> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
>>> index 4ae967bcf954..24087dfa4dcd 100644
>>> --- a/mm/mempolicy.c
>>> +++ b/mm/mempolicy.c
>>> @@ -411,6 +411,9 @@ struct queue_pages {
>>> unsigned long flags;
>>> nodemask_t *nmask;
>>> struct vm_area_struct *prev;
>>> + unsigned long start;
>>> + unsigned long end;
>>> + int in_hole;
>>> };
>>>
>>> /*
>>> @@ -618,28 +621,31 @@ static int queue_pages_test_walk(unsigned long start, unsigned long end,
>>> unsigned long endvma = vma->vm_end;
>>> unsigned long flags = qp->flags;
>>>
>>> - /*
>>> - * Need check MPOL_MF_STRICT to return -EIO if possible
>>> - * regardless of vma_migratable
>>> - */
>>> - if (!vma_migratable(vma) &&
>>> - !(flags & MPOL_MF_STRICT))
>>> - return 1;
>>> -
>>> + /* range check first */
>>> if (endvma > end)
>>> endvma = end;
>>> - if (vma->vm_start > start)
>>> - start = vma->vm_start;
>>> + BUG_ON((vma->vm_start > start) || (vma->vm_end < end));
>>>
>>> + qp->in_hole = 0;
>>> if (!(flags & MPOL_MF_DISCONTIG_OK)) {
>>> - if (!vma->vm_next && vma->vm_end < end)
>>> + if ((!vma->vm_next && vma->vm_end < qp->end) ||
>>> + (vma->vm_next && qp->end < vma->vm_next->vm_start))
>>> return -EFAULT;
>>> - if (qp->prev && qp->prev->vm_end < vma->vm_start)
>>> + if ((qp->prev && qp->prev->vm_end < vma->vm_start) ||
>>> + (!qp->prev && qp->start < vma->vm_start))
>>> return -EFAULT;
>>> }
>>>
>>> qp->prev = vma;
>>>
>>> + /*
>>> + * Need check MPOL_MF_STRICT to return -EIO if possible
>>> + * regardless of vma_migratable
>>> + */
>>> + if (!vma_migratable(vma) &&
>>> + !(flags & MPOL_MF_STRICT))
>>> + return 1;
>>> +
>>> if (flags & MPOL_MF_LAZY) {
>>> /* Similar to task_numa_work, skip inaccessible VMAs */
>>> if (!is_vm_hugetlb_page(vma) &&
>>> @@ -679,14 +685,23 @@ queue_pages_range(struct mm_struct *mm, unsigned long start, unsigned long end,
>>> nodemask_t *nodes, unsigned long flags,
>>> struct list_head *pagelist)
>>> {
>>> + int err;
>>> struct queue_pages qp = {
>>> .pagelist = pagelist,
>>> .flags = flags,
>>> .nmask = nodes,
>>> .prev = NULL,
>>> + .start = start,
>>> + .end = end,
>>> + .in_hole = 1,
>>> };
>>>
>>> - return walk_page_range(mm, start, end, &queue_pages_walk_ops, &qp);
>>> + err = walk_page_range(mm, start, end, &queue_pages_walk_ops, &qp);
>>> + /* whole range in unmapped hole */
>>> + if (qp->in_hole && !(flags & MPOL_MF_DISCONTIG_OK))
>>> + err = -EFAULT;
>>> +
>>> + return err;
>>> }
>>>
>>> /*
>>> @@ -738,8 +753,7 @@ static int mbind_range(struct mm_struct *mm, unsigned long start,
>>> unsigned long vmend;
>>>
>>> vma = find_vma(mm, start);
>>> - if (!vma || vma->vm_start > start)
>>> - return -EFAULT;
>>> + BUG_ON(!vma);
>>>
>>> prev = vma->vm_prev;
>>> if (start > vma->vm_start)
>>> --
>>> 2.22.0
Powered by blists - more mailing lists