From: Steven Price steven.price@arm.com
[ Upstream commit 8782fb61cc848364e1e1599d76d3c9dd58a1cc06 ]
The mmap lock protects the page walker from changes to the page tables during the walk. However a read lock is insufficient to protect those areas which don't have a VMA as munmap() detaches the VMAs before downgrading to a read lock and actually tearing down PTEs/page tables.
For users of walk_page_range() the solution is to simply call pte_hole() immediately without checking the actual page tables when a VMA is not present. We now never call __walk_page_range() without a valid vma.
For walk_page_range_novma() the locking requirements are tightened to require the mmap write lock to be taken, and then walking the pgd directly with 'no_vma' set.
This in turn means that all page walkers either have a valid vma, or it's that special 'novma' case for page table debugging. As a result, all the odd '(!walk->vma && !walk->no_vma)' tests can be removed.
Fixes: dd2283f2605e ("mm: mmap: zap pages with read mmap_sem in munmap") Reported-by: Jann Horn jannh@google.com Signed-off-by: Steven Price steven.price@arm.com Cc: Vlastimil Babka vbabka@suse.cz Cc: Thomas Hellström thomas.hellstrom@linux.intel.com Cc: Konstantin Khlebnikov koct9i@gmail.com Cc: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Sasha Levin sashal@kernel.org --- arch/riscv/mm/pageattr.c | 4 ++-- mm/pagewalk.c | 21 ++++++++++++--------- mm/ptdump.c | 4 ++-- 3 files changed, 16 insertions(+), 13 deletions(-)
diff --git a/arch/riscv/mm/pageattr.c b/arch/riscv/mm/pageattr.c index 5e49e4b4a4ccc..86c56616e5dea 100644 --- a/arch/riscv/mm/pageattr.c +++ b/arch/riscv/mm/pageattr.c @@ -118,10 +118,10 @@ static int __set_memory(unsigned long addr, int numpages, pgprot_t set_mask, if (!numpages) return 0;
- mmap_read_lock(&init_mm); + mmap_write_lock(&init_mm); ret = walk_page_range_novma(&init_mm, start, end, &pageattr_ops, NULL, &masks); - mmap_read_unlock(&init_mm); + mmap_write_unlock(&init_mm);
flush_tlb_kernel_range(start, end);
diff --git a/mm/pagewalk.c b/mm/pagewalk.c index 9b3db11a4d1db..fa7a3d21a7518 100644 --- a/mm/pagewalk.c +++ b/mm/pagewalk.c @@ -110,7 +110,7 @@ static int walk_pmd_range(pud_t *pud, unsigned long addr, unsigned long end, do { again: next = pmd_addr_end(addr, end); - if (pmd_none(*pmd) || (!walk->vma && !walk->no_vma)) { + if (pmd_none(*pmd)) { if (ops->pte_hole) err = ops->pte_hole(addr, next, depth, walk); if (err) @@ -171,7 +171,7 @@ static int walk_pud_range(p4d_t *p4d, unsigned long addr, unsigned long end, do { again: next = pud_addr_end(addr, end); - if (pud_none(*pud) || (!walk->vma && !walk->no_vma)) { + if (pud_none(*pud)) { if (ops->pte_hole) err = ops->pte_hole(addr, next, depth, walk); if (err) @@ -366,19 +366,19 @@ static int __walk_page_range(unsigned long start, unsigned long end, struct vm_area_struct *vma = walk->vma; const struct mm_walk_ops *ops = walk->ops;
- if (vma && ops->pre_vma) { + if (ops->pre_vma) { err = ops->pre_vma(start, end, walk); if (err) return err; }
- if (vma && is_vm_hugetlb_page(vma)) { + if (is_vm_hugetlb_page(vma)) { if (ops->hugetlb_entry) err = walk_hugetlb_range(start, end, walk); } else err = walk_pgd_range(start, end, walk);
- if (vma && ops->post_vma) + if (ops->post_vma) ops->post_vma(walk);
return err; @@ -450,9 +450,13 @@ int walk_page_range(struct mm_struct *mm, unsigned long start, if (!vma) { /* after the last vma */ walk.vma = NULL; next = end; + if (ops->pte_hole) + err = ops->pte_hole(start, next, -1, &walk); } else if (start < vma->vm_start) { /* outside vma */ walk.vma = NULL; next = min(end, vma->vm_start); + if (ops->pte_hole) + err = ops->pte_hole(start, next, -1, &walk); } else { /* inside vma */ walk.vma = vma; next = min(end, vma->vm_end); @@ -470,9 +474,8 @@ int walk_page_range(struct mm_struct *mm, unsigned long start, } if (err < 0) break; - } - if (walk.vma || walk.ops->pte_hole) err = __walk_page_range(start, next, &walk); + } if (err) break; } while (start = next, start < end); @@ -501,9 +504,9 @@ int walk_page_range_novma(struct mm_struct *mm, unsigned long start, if (start >= end || !walk.mm) return -EINVAL;
- mmap_assert_locked(walk.mm); + mmap_assert_write_locked(walk.mm);
- return __walk_page_range(start, end, &walk); + return walk_pgd_range(start, end, &walk); }
int walk_page_vma(struct vm_area_struct *vma, const struct mm_walk_ops *ops, diff --git a/mm/ptdump.c b/mm/ptdump.c index eea3d28d173c2..8adab455a68b3 100644 --- a/mm/ptdump.c +++ b/mm/ptdump.c @@ -152,13 +152,13 @@ void ptdump_walk_pgd(struct ptdump_state *st, struct mm_struct *mm, pgd_t *pgd) { const struct ptdump_range *range = st->range;
- mmap_read_lock(mm); + mmap_write_lock(mm); while (range->start != range->end) { walk_page_range_novma(mm, range->start, range->end, &ptdump_ops, pgd, st); range++; } - mmap_read_unlock(mm); + mmap_write_unlock(mm);
/* Flush out the last page */ st->note_page(st, 0, -1, 0);