Re: [PATCH] mm/page_table_check: fix accessing unmapped ptep

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On 2022/5/26 7:33 PM, Miaohe Lin wrote:
ptep is unmapped too early, so ptep will be accessed while it's unmapped.
Fix it by deferring pte_unmap() until page table checking is done.

In the beginning, page_table_check only supported x86_64, so there
is no problem. But then the commit 3fee229a8eb9 ("riscv/mm: enable
ARCH_SUPPORTS_PAGE_TABLE_CHECK") added support for riscv-32, it is indeed a problem in this case.

So:

Reviewed-by: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>


Fixes: 80110bbfbba6 ("mm/page_table_check: check entries at pmd levels")
Signed-off-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>
---
  mm/page_table_check.c | 2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/page_table_check.c b/mm/page_table_check.c
index 3692bea2ea2c..971c3129b0e3 100644
--- a/mm/page_table_check.c
+++ b/mm/page_table_check.c
@@ -234,11 +234,11 @@ void __page_table_check_pte_clear_range(struct mm_struct *mm,
  		pte_t *ptep = pte_offset_map(&pmd, addr);
  		unsigned long i;
- pte_unmap(ptep);
  		for (i = 0; i < PTRS_PER_PTE; i++) {
  			__page_table_check_pte_clear(mm, addr, *ptep);
  			addr += PAGE_SIZE;
  			ptep++;
  		}
+		pte_unmap(ptep);
  	}
  }

--
Thanks,
Qi




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