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mm/memory.c: recheck page table entry with page table lock held
commit ff09d7ec97
upstream.
We clear the pte temporarily during read/modify/write update of the pte.
If we take a page fault while the pte is cleared, the application can get
SIGBUS. One such case is with remap_pfn_range without a backing
vm_ops->fault callback. do_fault will return SIGBUS in that case.
cpu 0 cpu1
mprotect()
ptep_modify_prot_start()/pte cleared.
.
. page fault.
.
.
prep_modify_prot_commit()
Fix this by taking page table lock and rechecking for pte_none.
[aneesh.kumar@linux.ibm.com: fix crash observed with syzkaller run]
Link: http://lkml.kernel.org/r/87va6bwlfg.fsf@linux.ibm.com
Link: http://lkml.kernel.org/r/20180926031858.9692-1-aneesh.kumar@linux.ibm.com
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Ido Schimmel <idosch@idosch.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
parent
3996e891ec
commit
5999609a93
1 changed files with 30 additions and 4 deletions
34
mm/memory.c
34
mm/memory.c
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@ -3745,10 +3745,36 @@ static vm_fault_t do_fault(struct vm_fault *vmf)
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struct vm_area_struct *vma = vmf->vma;
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vm_fault_t ret;
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/* The VMA was not fully populated on mmap() or missing VM_DONTEXPAND */
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if (!vma->vm_ops->fault)
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ret = VM_FAULT_SIGBUS;
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else if (!(vmf->flags & FAULT_FLAG_WRITE))
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/*
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* The VMA was not fully populated on mmap() or missing VM_DONTEXPAND
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*/
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if (!vma->vm_ops->fault) {
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/*
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* If we find a migration pmd entry or a none pmd entry, which
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* should never happen, return SIGBUS
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*/
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if (unlikely(!pmd_present(*vmf->pmd)))
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ret = VM_FAULT_SIGBUS;
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else {
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vmf->pte = pte_offset_map_lock(vmf->vma->vm_mm,
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vmf->pmd,
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vmf->address,
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&vmf->ptl);
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/*
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* Make sure this is not a temporary clearing of pte
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* by holding ptl and checking again. A R/M/W update
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* of pte involves: take ptl, clearing the pte so that
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* we don't have concurrent modification by hardware
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* followed by an update.
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*/
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if (unlikely(pte_none(*vmf->pte)))
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ret = VM_FAULT_SIGBUS;
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else
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ret = VM_FAULT_NOPAGE;
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pte_unmap_unlock(vmf->pte, vmf->ptl);
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}
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} else if (!(vmf->flags & FAULT_FLAG_WRITE))
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ret = do_read_fault(vmf);
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else if (!(vma->vm_flags & VM_SHARED))
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ret = do_cow_fault(vmf);
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