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From:   Sasha Levin <Alexander.Levin@microsoft.com>
To:     "stable@vger.kernel.org" <stable@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
CC:     Jiang Biao <jiang.biao2@zte.com.cn>,
        Thomas Gleixner <tglx@linutronix.de>,
        "dave.hansen@linux.intel.com" <dave.hansen@linux.intel.com>,
        "luto@kernel.org" <luto@kernel.org>,
        "hpa@zytor.com" <hpa@zytor.com>,
        "albcamus@gmail.com" <albcamus@gmail.com>,
        "zhong.weidong@zte.com.cn" <zhong.weidong@zte.com.cn>,
        Sasha Levin <Alexander.Levin@microsoft.com>
Subject: [PATCH AUTOSEL 4.18 86/88] x86/pti: Check the return value of
 pti_user_pagetable_walk_pmd()
Thread-Topic: [PATCH AUTOSEL 4.18 86/88] x86/pti: Check the return value of
 pti_user_pagetable_walk_pmd()
Thread-Index: AQHURkLe7723AeOjFkq8IrB4nNdPTQ==
Date:   Fri, 7 Sep 2018 00:36:52 +0000
Message-ID: <20180907003547.57567-86-alexander.levin@microsoft.com>
References: <20180907003547.57567-1-alexander.levin@microsoft.com>
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From: Jiang Biao <jiang.biao2@zte.com.cn>

[ Upstream commit 8c934e01a7ce685d98e970880f5941d79272c654 ]

pti_user_pagetable_walk_pmd() can return NULL, so the return value should
be checked to prevent a NULL pointer dereference.

Add the check and a warning when the PMD allocation fails.

Signed-off-by: Jiang Biao <jiang.biao2@zte.com.cn>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: dave.hansen@linux.intel.com
Cc: luto@kernel.org
Cc: hpa@zytor.com
Cc: albcamus@gmail.com
Cc: zhong.weidong@zte.com.cn
Link: https://lkml.kernel.org/r/1532045192-49622-2-git-send-email-jiang.bia=
o2@zte.com.cn
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
---
 arch/x86/mm/pti.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/arch/x86/mm/pti.c b/arch/x86/mm/pti.c
index 51abd8292b6d..ffa2f0f67904 100644
--- a/arch/x86/mm/pti.c
+++ b/arch/x86/mm/pti.c
@@ -206,7 +206,7 @@ static pmd_t *pti_user_pagetable_walk_pmd(unsigned long=
 address)
 	BUILD_BUG_ON(p4d_large(*p4d) !=3D 0);
 	if (p4d_none(*p4d)) {
 		unsigned long new_pud_page =3D __get_free_page(gfp);
-		if (!new_pud_page)
+		if (WARN_ON_ONCE(!new_pud_page))
 			return NULL;
=20
 		set_p4d(p4d, __p4d(_KERNPG_TABLE | __pa(new_pud_page)));
@@ -220,7 +220,7 @@ static pmd_t *pti_user_pagetable_walk_pmd(unsigned long=
 address)
 	}
 	if (pud_none(*pud)) {
 		unsigned long new_pmd_page =3D __get_free_page(gfp);
-		if (!new_pmd_page)
+		if (WARN_ON_ONCE(!new_pmd_page))
 			return NULL;
=20
 		set_pud(pud, __pud(_KERNPG_TABLE | __pa(new_pmd_page)));
@@ -242,9 +242,13 @@ static pmd_t *pti_user_pagetable_walk_pmd(unsigned lon=
g address)
 static __init pte_t *pti_user_pagetable_walk_pte(unsigned long address)
 {
 	gfp_t gfp =3D (GFP_KERNEL | __GFP_NOTRACK | __GFP_ZERO);
-	pmd_t *pmd =3D pti_user_pagetable_walk_pmd(address);
+	pmd_t *pmd;
 	pte_t *pte;
=20
+	pmd =3D 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)) {
 		WARN_ON(1);
--=20
2.17.1