linux-kernel - [PATCH 2/5] x86/pti: check the return value of pti_user_pagetable_walk

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Date:   Mon, 16 Jul 2018 12:03:37 +0800
From:   Jiang Biao <jiang.biao2@....com.cn>
To:     tglx@...utronix.de, mingo@...hat.com
Cc:     dave.hansen@...ux.intel.com, luto@...nel.org, hpa@...or.com,
        x86@...nel.org, albcamus@...il.com, linux-kernel@...r.kernel.org,
        zhong.weidong@....com.cn, jiang.biao2@....com.cn
Subject: [PATCH 2/5] x86/pti: check the return value of pti_user_pagetable_walk_pmd

pti_user_pagetable_walk_pmd() may return NULL, we should check the
return value in pti_user_pagetable_walk_pte() to avoid NULL pointer
dereference like it is checked in pti_clone_pmds().

Signed-off-by: Jiang Biao <jiang.biao2@....com.cn>
---
 arch/x86/mm/pti.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/x86/mm/pti.c b/arch/x86/mm/pti.c
index be9e5bc..bb6f608 100644
--- a/arch/x86/mm/pti.c
+++ b/arch/x86/mm/pti.c
@@ -239,8 +239,10 @@ static pmd_t *pti_user_pagetable_walk_pmd(unsigned long address)
 static __init pte_t *pti_user_pagetable_walk_pte(unsigned long address)
 {
 	gfp_t gfp = (GFP_KERNEL | __GFP_NOTRACK | __GFP_ZERO);
-	pmd_t *pmd = pti_user_pagetable_walk_pmd(address);
 	pte_t *pte;
+	pmd_t *pmd = pti_user_pagetable_walk_pmd(address);
+	if (WARN_ON(!pmd))
+		return NULL;
 
 	/* We can't do anything sensible if we hit a large mapping. */
 	if (pmd_large(*pmd)) {
-- 
2.7.4