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[148.163.156.1]) by mx.google.com with ESMTPS id p17si5604641pge.55.2017.07.13.21.51.39 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 13 Jul 2017 21:51:39 -0700 (PDT) Received: from pps.filterd (m0098410.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.21/8.16.0.21) with SMTP id v6E4miC5042833 for ; Fri, 14 Jul 2017 00:51:39 -0400 Received: from e23smtp07.au.ibm.com (e23smtp07.au.ibm.com [202.81.31.140]) by mx0a-001b2d01.pphosted.com with ESMTP id 2bpmfsnd49-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Fri, 14 Jul 2017 00:51:38 -0400 Received: from localhost by e23smtp07.au.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Fri, 14 Jul 2017 14:51:36 +1000 Received: from d23av01.au.ibm.com (d23av01.au.ibm.com [9.190.234.96]) by d23relay08.au.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id v6E4pZTQ24313880 for ; Fri, 14 Jul 2017 14:51:35 +1000 Received: from d23av01.au.ibm.com (localhost [127.0.0.1]) by d23av01.au.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id v6E4pYdx021473 for ; Fri, 14 Jul 2017 14:51:34 +1000 Subject: Re: [PATCH] mm/mremap: Fail map duplication attempts for private mappings 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> From: Anshuman Khandual Date: Fri, 14 Jul 2017 10:21:26 +0530 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 Message-Id: Sender: owner-linux-mm@kvack.org List-ID: To: Mike Kravetz , Vlastimil Babka , linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: Andrew Morton , Andrea Arcangeli , Michal Hocko , Aaron Lu , "Kirill A . Shutemov" , Anshuman Khandual , Linux API 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. -- 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