linux-kernel - [PATCH V3 2/3] mm/ksm: Handle protnone saved writes when making page write protect

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Date:   Sun, 19 Feb 2017 15:33:44 +0530
From:   "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To:     akpm@...ux-foundation.org, Rik van Riel <riel@...riel.com>,
        Mel Gorman <mgorman@...hsingularity.net>, paulus@...abs.org,
        benh@...nel.crashing.org
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Subject: [PATCH V3 2/3] mm/ksm: Handle protnone saved writes when making page write protect

Without this KSM will consider the page write protected, but a numa fault can
later mark the page writable. This can result in memory corruption.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>
---
 include/asm-generic/pgtable.h | 8 ++++++++
 mm/ksm.c                      | 9 +++++++--
 2 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pgtable.h
index b6f3a8a4b738..8c8ba48bef0b 100644
--- a/include/asm-generic/pgtable.h
+++ b/include/asm-generic/pgtable.h
@@ -200,6 +200,10 @@ static inline void ptep_set_wrprotect(struct mm_struct *mm, unsigned long addres
 #define pte_mk_savedwrite pte_mkwrite
 #endif
 
+#ifndef pte_clear_savedwrite
+#define pte_clear_savedwrite pte_wrprotect
+#endif
+
 #ifndef pmd_savedwrite
 #define pmd_savedwrite pmd_write
 #endif
@@ -208,6 +212,10 @@ static inline void ptep_set_wrprotect(struct mm_struct *mm, unsigned long addres
 #define pmd_mk_savedwrite pmd_mkwrite
 #endif
 
+#ifndef pmd_clear_savedwrite
+#define pmd_clear_savedwrite pmd_wrprotect
+#endif
+
 #ifndef __HAVE_ARCH_PMDP_SET_WRPROTECT
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 static inline void pmdp_set_wrprotect(struct mm_struct *mm,
diff --git a/mm/ksm.c b/mm/ksm.c
index 9ae6011a41f8..768202831578 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -872,7 +872,8 @@ static int write_protect_page(struct vm_area_struct *vma, struct page *page,
 	if (!ptep)
 		goto out_mn;
 
-	if (pte_write(*ptep) || pte_dirty(*ptep)) {
+	if (pte_write(*ptep) || pte_dirty(*ptep) ||
+	    (pte_protnone(*ptep) && pte_savedwrite(*ptep))) {
 		pte_t entry;
 
 		swapped = PageSwapCache(page);
@@ -897,7 +898,11 @@ static int write_protect_page(struct vm_area_struct *vma, struct page *page,
 		}
 		if (pte_dirty(entry))
 			set_page_dirty(page);
-		entry = pte_mkclean(pte_wrprotect(entry));
+
+		if (pte_protnone(entry))
+			entry = pte_mkclean(pte_clear_savedwrite(entry));
+		else
+			entry = pte_mkclean(pte_wrprotect(entry));
 		set_pte_at_notify(mm, addr, ptep, entry);
 	}
 	*orig_pte = *ptep;
-- 
2.7.4