From: Miaohe Lin <linmiaohe@huawei.com>
Date: Thu, 26 May 2022 11:33:50 +0000 (+0800)
Subject: mm/page_table_check: fix accessing unmapped ptep
X-Git-Tag: v6.6.17~7420^2
X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=24c8e27e63224ce832b4723cb60632d3eddb55de;p=platform%2Fkernel%2Flinux-rpi.git

mm/page_table_check: fix accessing unmapped ptep

ptep is unmapped too early, so ptep could theoretically be accessed while
it's unmapped.  This might become a problem if/when CONFIG_HIGHPTE becomes
available on riscv.

Fix it by deferring pte_unmap() until page table checking is done.

[akpm@linux-foundation.org: account for ptep alteration, per Matthew]
Link: https://lkml.kernel.org/r/20220526113350.30806-1-linmiaohe@huawei.com
Fixes: 80110bbfbba6 ("mm/page_table_check: check entries at pmd levels")
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Acked-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Cc: Qi Zheng <zhengqi.arch@bytedance.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

diff --git a/mm/page_table_check.c b/mm/page_table_check.c
index 2458281..bc55be2 100644
--- a/mm/page_table_check.c
+++ b/mm/page_table_check.c
@@ -251,11 +251,11 @@ 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 - PTRS_PER_PTE);
 	}
 }