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From:   Jiang Biao <jiang.biao2@zte.com.cn>
To:     tglx@linutronix.de, mingo@redhat.com
Cc:     dave.hansen@linux.intel.com, luto@kernel.org, hpa@zytor.com,
        x86@kernel.org, albcamus@gmail.com, linux-kernel@vger.kernel.org,
        zhong.weidong@zte.com.cn, jiang.biao2@zte.com.cn
Subject: [PATCH v2 2/2] x86/pti: check the return value of pti_user_pagetable_walk_pmd
Date:   Tue, 17 Jul 2018 15:23:22 +0800
Message-Id: <1531812202-37778-2-git-send-email-jiang.biao2@zte.com.cn>
In-Reply-To: <1531812202-37778-1-git-send-email-jiang.biao2@zte.com.cn>
References: <1531812202-37778-1-git-send-email-jiang.biao2@zte.com.cn>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Check the return value of pti_user_pagetable_walk_pmd() to avoid
NULL pointer dereference. And add warning for fail allocation.

Signed-off-by: Jiang Biao <jiang.biao2@zte.com.cn>
---
 arch/x86/mm/pti.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/arch/x86/mm/pti.c b/arch/x86/mm/pti.c
index 7c402e9..3dba6a7 100644
--- a/arch/x86/mm/pti.c
+++ b/arch/x86/mm/pti.c
@@ -203,7 +203,7 @@ static pmd_t *pti_user_pagetable_walk_pmd(unsigned long address)
 	BUILD_BUG_ON(p4d_large(*p4d) != 0);
 	if (p4d_none(*p4d)) {
 		unsigned long new_pud_page = __get_free_page(gfp);
-		if (!new_pud_page)
+		if (WARN_ON(!new_pud_page))
 			return NULL;
 
 		set_p4d(p4d, __p4d(_KERNPG_TABLE | __pa(new_pud_page)));
@@ -217,7 +217,7 @@ static pmd_t *pti_user_pagetable_walk_pmd(unsigned long address)
 	}
 	if (pud_none(*pud)) {
 		unsigned long new_pmd_page = __get_free_page(gfp);
-		if (!new_pmd_page)
+		if (WARN_ON(!new_pmd_page))
 			return NULL;
 
 		set_pud(pud, __pud(_KERNPG_TABLE | __pa(new_pmd_page)));
@@ -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 (!pmd)
+		return NULL;
 
 	/* We can't do anything sensible if we hit a large mapping. */
 	if (pmd_large(*pmd)) {
-- 
2.7.4