linux-kernel - [PATCH 02/14] arm: adjust_pte() use pte_offset_map_maywrite

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Message-Id: <3d151aaf876b93a97fd3f070780345a3bf572123.1724226076.git.zhengqi.arch@bytedance.com>
Date: Wed, 21 Aug 2024 16:18:45 +0800
From: Qi Zheng <zhengqi.arch@...edance.com>
To: david@...hat.com,
	hughd@...gle.com,
	willy@...radead.org,
	muchun.song@...ux.dev,
	vbabka@...nel.org,
	akpm@...ux-foundation.org,
	rppt@...nel.org,
	vishal.moola@...il.com,
	peterx@...hat.com,
	ryan.roberts@....com
Cc: linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	linux-arm-kernel@...ts.infradead.org,
	linuxppc-dev@...ts.ozlabs.org,
	Qi Zheng <zhengqi.arch@...edance.com>
Subject: [PATCH 02/14] arm: adjust_pte() use pte_offset_map_maywrite_nolock()

In do_adjust_pte(), we may modify the pte entry. At this time, the write
lock of mmap_lock is not held, and the pte_same() check is not performed
after the PTL held. The corresponding pmd entry may have been modified
concurrently. Therefore, in order to ensure the stability if pmd entry,
use pte_offset_map_maywrite_nolock() to replace pte_offset_map_nolock(),
and do pmd_same() check after holding the PTL.

Signed-off-by: Qi Zheng <zhengqi.arch@...edance.com>
---
 arch/arm/mm/fault-armv.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/arch/arm/mm/fault-armv.c b/arch/arm/mm/fault-armv.c
index 831793cd6ff94..5371920ec0550 100644
--- a/arch/arm/mm/fault-armv.c
+++ b/arch/arm/mm/fault-armv.c
@@ -94,6 +94,7 @@ static int adjust_pte(struct vm_area_struct *vma, unsigned long address,
 	pud_t *pud;
 	pmd_t *pmd;
 	pte_t *pte;
+	pmd_t pmdval;
 	int ret;
 
 	pgd = pgd_offset(vma->vm_mm, address);
@@ -112,16 +113,22 @@ static int adjust_pte(struct vm_area_struct *vma, unsigned long address,
 	if (pmd_none_or_clear_bad(pmd))
 		return 0;
 
+again:
 	/*
 	 * This is called while another page table is mapped, so we
 	 * must use the nested version.  This also means we need to
 	 * open-code the spin-locking.
 	 */
-	pte = pte_offset_map_nolock(vma->vm_mm, pmd, address, &ptl);
+	pte = pte_offset_map_maywrite_nolock(vma->vm_mm, pmd, address, &pmdval, &ptl);
 	if (!pte)
 		return 0;
 
 	do_pte_lock(ptl);
+	if (unlikely(!pmd_same(pmdval, pmdp_get_lockless(pmd)))) {
+		do_pte_unlock(ptl);
+		pte_unmap(pte);
+		goto again;
+	}
 
 	ret = do_adjust_pte(vma, address, pfn, pte);
 
-- 
2.20.1