From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg0-f71.google.com (mail-pg0-f71.google.com [74.125.83.71]) by kanga.kvack.org (Postfix) with ESMTP id 22D3A6B027E for ; Wed, 22 Nov 2017 07:47:26 -0500 (EST) Received: by mail-pg0-f71.google.com with SMTP id r12so16138422pgu.9 for ; Wed, 22 Nov 2017 04:47:26 -0800 (PST) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id h89si4588361pld.202.2017.11.22.04.47.24 for (version=TLS1 cipher=AES128-SHA bits=128/128); Wed, 22 Nov 2017 04:47:25 -0800 (PST) Date: Wed, 22 Nov 2017 13:47:23 +0100 From: Michal Hocko Subject: Re: [PATCH] mm/hugetlb: Fix NULL-pointer dereference on 5-level paging machine Message-ID: <20171122124723.pr2yazh2g3zqjula@dhcp22.suse.cz> References: <20171122121921.64822-1-kirill.shutemov@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20171122121921.64822-1-kirill.shutemov@linux.intel.com> Sender: owner-linux-mm@kvack.org List-ID: To: "Kirill A. Shutemov" Cc: Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-api@vger.kernel.org, stable@vger.kernel.org On Wed 22-11-17 15:19:21, 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. Ups, I have completely missed that when reviewing the patch. Sorry about that. > 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: Michal Hocko > --- > 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) { > -- > 2.15.0 -- Michal Hocko SUSE Labs -- 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