On Tue, 25 Jun 2024 14:06:43 -0700 Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote: > On Wed, 13 Mar 2024 09:29:13 +0800 Peng Zhang <zhangpeng362@xxxxxxxxxx> wrote: > > > From: ZhangPeng <zhangpeng362@xxxxxxxxxx> > > > > The vmf->ptl in filemap_fault_recheck_pte_none() is still set from > > handle_pte_fault(). But at the same time, we did a pte_unmap(vmf->pte). > > After a pte_unmap(vmf->pte) unmap and rcu_read_unlock(), the page table > > may be racily changed and vmf->ptl maybe fails to protect the actual > > page table. > > Fix this by replacing pte_offset_map() with pte_offset_map_nolock(). > > > > ... > > > > --- a/mm/filemap.c > > +++ b/mm/filemap.c > > @@ -3207,7 +3207,8 @@ static vm_fault_t filemap_fault_recheck_pte_none(struct vm_fault *vmf) > > if (!(vmf->flags & FAULT_FLAG_ORIG_PTE_VALID)) > > return 0; > > > > - ptep = pte_offset_map(vmf->pmd, vmf->address); > > + ptep = pte_offset_map_nolock(vma->vm_mm, vmf->pmd, vmf->address, > > + &vmf->ptl); > > if (unlikely(!ptep)) > > return VM_FAULT_NOPAGE; > > > > whoops, I'm still sitting on this because I didn't know whether we > should backport it. > > And... guess what I say next. Can we please describe what are the > userspace visible effects of the bug? > Nobody? Oh well, I'll add cc:stable amd move this into mm-hotfixes. From: ZhangPeng <zhangpeng362@xxxxxxxxxx> Subject: filemap: replace pte_offset_map() with pte_offset_map_nolock() Date: Wed, 13 Mar 2024 09:29:13 +0800 The vmf->ptl in filemap_fault_recheck_pte_none() is still set from handle_pte_fault(). But at the same time, we did a pte_unmap(vmf->pte). After a pte_unmap(vmf->pte) unmap and rcu_read_unlock(), the page table may be racily changed and vmf->ptl maybe fails to protect the actual page table. Fix this by replacing pte_offset_map() with pte_offset_map_nolock(). Link: https://lkml.kernel.org/r/20240313012913.2395414-1-zhangpeng362@xxxxxxxxxx Fixes: 58f327f2ce80 ("filemap: avoid unnecessary major faults in filemap_fault()") Signed-off-by: ZhangPeng <zhangpeng362@xxxxxxxxxx> Suggested-by: David Hildenbrand <david@xxxxxxxxxx> Reviewed-by: David Hildenbrand <david@xxxxxxxxxx> Cc: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxx> Cc: "Huang, Ying" <ying.huang@xxxxxxxxx> Cc: Hugh Dickins <hughd@xxxxxxxxxx> Cc: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx> Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx> Cc: Nanyong Sun <sunnanyong@xxxxxxxxxx> Cc: Yang Shi <shy828301@xxxxxxxxx> Cc: Yin Fengwei <fengwei.yin@xxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/filemap.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) --- a/mm/filemap.c~filemap-replace-pte_offset_map-with-pte_offset_map_nolock +++ a/mm/filemap.c @@ -3231,7 +3231,8 @@ static vm_fault_t filemap_fault_recheck_ if (!(vmf->flags & FAULT_FLAG_ORIG_PTE_VALID)) return 0; - ptep = pte_offset_map(vmf->pmd, vmf->address); + ptep = pte_offset_map_nolock(vma->vm_mm, vmf->pmd, vmf->address, + &vmf->ptl); if (unlikely(!ptep)) return VM_FAULT_NOPAGE; _
