From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wr0-f197.google.com (mail-wr0-f197.google.com [209.85.128.197]) by kanga.kvack.org (Postfix) with ESMTP id D1A8C6B0275 for ; Wed, 22 Nov 2017 07:36:47 -0500 (EST) Received: by mail-wr0-f197.google.com with SMTP id f9so10067344wra.2 for ; Wed, 22 Nov 2017 04:36:47 -0800 (PST) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id c40si2405840edf.117.2017.11.22.04.36.46 for (version=TLS1 cipher=AES128-SHA bits=128/128); Wed, 22 Nov 2017 04:36:46 -0800 (PST) Subject: Re: [PATCH] mm/hugetlb: Fix NULL-pointer dereference on 5-level paging machine References: <20171122121921.64822-1-kirill.shutemov@linux.intel.com> From: Vlastimil Babka Message-ID: <88a7a176-6070-2bf1-4579-d5fccdfc7f37@suse.cz> Date: Wed, 22 Nov 2017 13:36:43 +0100 MIME-Version: 1.0 In-Reply-To: <20171122121921.64822-1-kirill.shutemov@linux.intel.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: "Kirill A. Shutemov" , Andrew Morton Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-api@vger.kernel.org, Michal Hocko , stable@vger.kernel.org On 11/22/2017 01:19 PM, Kirill A. Shutemov wrote: > I've made mistake during converting hugetlb code to 5-level paging: > in huge_pte_alloc() we have to use p4d_alloc(), not p4d_offset(). > Otherwise it leads to crash -- NULL-pointer dereference in pud_alloc() > if p4d table is not yet allocated. > > It only can happen in 5-level paging mode. In 4-level paging mode > p4d_offset() always returns pgd, so we are fine. > > Signed-off-by: Kirill A. Shutemov > Fixes: c2febafc6773 ("mm: convert generic code to 5-level paging") > Cc: # v4.11+ Acked-by: Vlastimil Babka > --- > mm/hugetlb.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/mm/hugetlb.c b/mm/hugetlb.c > index 2d2ff5e8bf2b..94a4c0b63580 100644 > --- a/mm/hugetlb.c > +++ b/mm/hugetlb.c > @@ -4617,7 +4617,9 @@ pte_t *huge_pte_alloc(struct mm_struct *mm, > pte_t *pte = NULL; > > pgd = pgd_offset(mm, addr); > - p4d = p4d_offset(pgd, addr); > + p4d = p4d_alloc(mm, pgd, addr); > + if (!p4d) > + return NULL; > pud = pud_alloc(mm, p4d, addr); > if (pud) { > if (sz == PUD_SIZE) { > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org