From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751410AbdGNEvp (ORCPT ); Fri, 14 Jul 2017 00:51:45 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:58085 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751383AbdGNEvn (ORCPT ); Fri, 14 Jul 2017 00:51:43 -0400 Subject: Re: [PATCH] mm/mremap: Fail map duplication attempts for private mappings To: Mike Kravetz , Vlastimil Babka , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <1499961495-8063-1-git-send-email-mike.kravetz@oracle.com> <4e921eb5-8741-3337-9a7d-5ec9473412da@suse.cz> <415625d2-1be9-71f0-ca11-a014cef98a3f@oracle.com> Cc: Andrew Morton , Andrea Arcangeli , Michal Hocko , Aaron Lu , "Kirill A . Shutemov" , Anshuman Khandual , Linux API From: Anshuman Khandual Date: Fri, 14 Jul 2017 10:21:26 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.5.1 MIME-Version: 1.0 In-Reply-To: <415625d2-1be9-71f0-ca11-a014cef98a3f@oracle.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-TM-AS-MML: disable x-cbid: 17071404-1617-0000-0000-000001F757B1 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17071404-1618-0000-0000-0000483FBA67 Message-Id: X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-07-13_13:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=0 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1706020000 definitions=main-1707140079 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07/14/2017 04:03 AM, Mike Kravetz wrote: > On 07/13/2017 12:11 PM, Vlastimil Babka wrote: >> [+CC linux-api] >> >> On 07/13/2017 05:58 PM, Mike Kravetz wrote: >>> mremap will create a 'duplicate' mapping if old_size == 0 is >>> specified. Such duplicate mappings make no sense for private >>> mappings. If duplication is attempted for a private mapping, >>> mremap creates a separate private mapping unrelated to the >>> original mapping and makes no modifications to the original. >>> This is contrary to the purpose of mremap which should return >>> a mapping which is in some way related to the original. >>> >>> Therefore, return EINVAL in the case where if an attempt is >>> made to duplicate a private mapping. >>> >>> Signed-off-by: Mike Kravetz >> Acked-by: Vlastimil Babka >> > In another e-mail thread, Andrea makes the case that mremap(old_size == 0) > of private file backed mappings could possibly be used for something useful. > For example to create a private COW mapping. Of course, a better way to do > this would be simply using the fd to create a private mapping. > > If returning EINVAL for all private mappings is too general, the following > patch adds a check to only return EINVAL for private anon mappings. > > mm/mremap: Fail map duplication attempts for private anon mappings > > mremap will create a 'duplicate' mapping if old_size == 0 is > specified. Such duplicate mappings make no sense for private > anonymous mappings. If duplication is attempted for a private > anon mapping, mremap creates a separate private mapping unrelated > to the original mapping and makes no modifications to the original. > This is contrary to the purpose of mremap which should return a > mapping which is in some way related to the original. > > Therefore, return EINVAL in the case where an attempt is made to > duplicate a private anon mapping. > > Signed-off-by: Mike Kravetz > --- > mm/mremap.c | 8 ++++++++ > 1 file changed, 8 insertions(+) > > diff --git a/mm/mremap.c b/mm/mremap.c > index cd8a1b1..586ea3d 100644 > --- a/mm/mremap.c > +++ b/mm/mremap.c > @@ -383,6 +383,14 @@ static struct vm_area_struct *vma_to_resize(unsigned long addr, > if (!vma || vma->vm_start > addr) > return ERR_PTR(-EFAULT); > > + /* > + * !old_len is a special case where a mapping is 'duplicated'. > + * Do not allow this for private anon mappings. > + */ > + if (!old_len && vma_is_anonymous(vma) && > + !(vma->vm_flags & (VM_SHARED | VM_MAYSHARE))) > + return ERR_PTR(-EINVAL); Sounds better compared to rejecting everything private.