From: Steven Price <steven.price@xxxxxxx>
[ 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@xxxxxxxxxx>
Signed-off-by: Steven Price <steven.price@xxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Thomas Hellström <thomas.hellstrom@xxxxxxxxxxxxxxx>
Cc: Konstantin Khlebnikov <koct9i@xxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
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);
--
2.35.1
