From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0a-001b2d01.pphosted.com (mx0b-001b2d01.pphosted.com [148.163.158.5]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 40GJw14VFWzDrnp for ; Wed, 4 Apr 2018 18:26:41 +1000 (AEST) Received: from pps.filterd (m0098414.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.22/8.16.0.22) with SMTP id w348QN13030407 for ; Wed, 4 Apr 2018 04:26:39 -0400 Received: from e06smtp14.uk.ibm.com (e06smtp14.uk.ibm.com [195.75.94.110]) by mx0b-001b2d01.pphosted.com with ESMTP id 2h4tv4rvny-1 (version=TLSv1.2 cipher=AES256-SHA256 bits=256 verify=NOT) for ; Wed, 04 Apr 2018 04:26:27 -0400 Received: from localhost by e06smtp14.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Wed, 4 Apr 2018 09:25:06 +0100 Subject: Re: [PATCH v9 09/24] mm: protect mremap() against SPF hanlder To: David Rientjes Cc: paulmck@linux.vnet.ibm.com, peterz@infradead.org, akpm@linux-foundation.org, kirill@shutemov.name, ak@linux.intel.com, mhocko@kernel.org, dave@stgolabs.net, jack@suse.cz, Matthew Wilcox , benh@kernel.crashing.org, mpe@ellerman.id.au, paulus@samba.org, Thomas Gleixner , Ingo Molnar , hpa@zytor.com, Will Deacon , Sergey Senozhatsky , Andrea Arcangeli , Alexei Starovoitov , kemi.wang@intel.com, sergey.senozhatsky.work@gmail.com, Daniel Jordan , linux-kernel@vger.kernel.org, linux-mm@kvack.org, haren@linux.vnet.ibm.com, khandual@linux.vnet.ibm.com, npiggin@gmail.com, bsingharora@gmail.com, Tim Chen , linuxppc-dev@lists.ozlabs.org, x86@kernel.org References: <1520963994-28477-1-git-send-email-ldufour@linux.vnet.ibm.com> <1520963994-28477-10-git-send-email-ldufour@linux.vnet.ibm.com> <1fe7529a-947c-fdb2-12d2-b38bdd41bb04@linux.vnet.ibm.com> From: Laurent Dufour Date: Wed, 4 Apr 2018 10:24:55 +0200 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Message-Id: List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On 28/03/2018 23:21, David Rientjes wrote: > On Wed, 28 Mar 2018, Laurent Dufour wrote: > >>>> @@ -326,7 +336,10 @@ static unsigned long move_vma(struct vm_area_struct *vma, >>>> mremap_userfaultfd_prep(new_vma, uf); >>>> arch_remap(mm, old_addr, old_addr + old_len, >>>> new_addr, new_addr + new_len); >>>> + if (vma != new_vma) >>>> + vm_raw_write_end(vma); >>>> } >>>> + vm_raw_write_end(new_vma); >>> >>> Just do >>> >>> vm_raw_write_end(vma); >>> vm_raw_write_end(new_vma); >>> >>> here. >> >> Are you sure ? we can have vma = new_vma done if (unlikely(err)) >> > > Sorry, what I meant was do > > if (vma != new_vma) > vm_raw_write_end(vma); > vm_raw_write_end(new_vma); > > after the conditional. Having the locking unnecessarily embedded in the > conditional has been an issue in the past with other areas of core code, > unless you have a strong reason for it. Unfortunately, I can't see how doing this in another way since vma = new_vma is done in the error branch. So releasing the VMAs outside of the conditional may lead to miss 'vma' if the error branch is taken. Here is the code snippet as a reminder: new_vma = copy_vma(&vma, new_addr, new_len, new_pgoff, &need_rmap_locks); [...] if (vma != new_vma) vm_raw_write_begin(vma); [...] if (unlikely(err)) { [...] if (vma != new_vma) vm_raw_write_end(vma); vma = new_vma; <<<< here we lost reference to vma [...] } else { [...] if (vma != new_vma) vm_raw_write_end(vma); } vm_raw_write_end(new_vma);