From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3E881C433DF for ; Fri, 10 Jul 2020 10:58:34 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id E56AC2078D for ; Fri, 10 Jul 2020 10:58:33 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E56AC2078D Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.cz Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 606386B0002; Fri, 10 Jul 2020 06:58:33 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 58D9A6B0005; Fri, 10 Jul 2020 06:58:33 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 47D9B8D0001; Fri, 10 Jul 2020 06:58:33 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0224.hostedemail.com [216.40.44.224]) by kanga.kvack.org (Postfix) with ESMTP id 2D8646B0002 for ; Fri, 10 Jul 2020 06:58:33 -0400 (EDT) Received: from smtpin24.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id 8468D5848 for ; Fri, 10 Jul 2020 10:58:32 +0000 (UTC) X-FDA: 77021867664.24.crime67_1b08db026ecd Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin24.hostedemail.com (Postfix) with ESMTP id 5DE5F1A4BB for ; Fri, 10 Jul 2020 10:58:32 +0000 (UTC) X-HE-Tag: crime67_1b08db026ecd X-Filterd-Recvd-Size: 3988 Received: from mx2.suse.de (mx2.suse.de [195.135.220.15]) by imf27.hostedemail.com (Postfix) with ESMTP for ; Fri, 10 Jul 2020 10:58:31 +0000 (UTC) X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 7A06BAD76; Fri, 10 Jul 2020 10:58:30 +0000 (UTC) Subject: Re: [PATCH] mm: Close race between munmap() and expand_upwards()/downwards() To: "Kirill A. Shutemov" , Andrew Morton Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Jann Horn , stable@vger.kernel.org, Yang Shi , Oleg Nesterov , Matthew Wilcox References: <20200709105309.42495-1-kirill.shutemov@linux.intel.com> From: Vlastimil Babka Message-ID: <6f96a9ed-3a24-2478-b84d-5e213baa16d4@suse.cz> Date: Fri, 10 Jul 2020 12:58:29 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.9.0 MIME-Version: 1.0 In-Reply-To: <20200709105309.42495-1-kirill.shutemov@linux.intel.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 5DE5F1A4BB X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam03 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 7/9/20 12:53 PM, Kirill A. Shutemov wrote: > VMA with VM_GROWSDOWN or VM_GROWSUP flag set can change their size under > mmap_read_lock(). It can lead to race with __do_munmap(): > > Thread A Thread B > __do_munmap() > detach_vmas_to_be_unmapped() > mmap_write_downgrade() > expand_downwards() > vma->vm_start = address; > // The VMA now overlaps with > // VMAs detached by the Thread A > // page fault populates expanded part > // of the VMA > unmap_region() > // Zaps pagetables partly > // populated by Thread B > > Similar race exists for expand_upwards(). > > The fix is to avoid downgrading mmap_lock in __do_munmap() if detached > VMAs are next to VM_GROWSDOWN or VM_GROWSUP VMA. > > Signed-off-by: Kirill A. Shutemov > Reported-by: Jann Horn > Fixes: dd2283f2605e ("mm: mmap: zap pages with read mmap_sem in munmap") > Cc: # 4.20 > Cc: Yang Shi > Cc: Vlastimil Babka > Cc: Oleg Nesterov > Cc: Matthew Wilcox Acked-by: Vlastimil Babka Thanks! > --- > mm/mmap.c | 16 ++++++++++++++-- > 1 file changed, 14 insertions(+), 2 deletions(-) > > diff --git a/mm/mmap.c b/mm/mmap.c > index 59a4682ebf3f..71df4b36b42a 100644 > --- a/mm/mmap.c > +++ b/mm/mmap.c > @@ -2620,7 +2620,7 @@ static void unmap_region(struct mm_struct *mm, > * Create a list of vma's touched by the unmap, removing them from the mm's > * vma list as we go.. > */ > -static void > +static bool > detach_vmas_to_be_unmapped(struct mm_struct *mm, struct vm_area_struct *vma, > struct vm_area_struct *prev, unsigned long end) > { > @@ -2645,6 +2645,17 @@ detach_vmas_to_be_unmapped(struct mm_struct *mm, struct vm_area_struct *vma, > > /* Kill the cache */ > vmacache_invalidate(mm); > + > + /* > + * Do not downgrade mmap_sem if we are next to VM_GROWSDOWN or > + * VM_GROWSUP VMA. Such VMAs can change their size under > + * down_read(mmap_sem) and collide with the VMA we are about to unmap. > + */ > + if (vma && (vma->vm_flags & VM_GROWSDOWN)) > + return false; > + if (prev && (prev->vm_flags & VM_GROWSUP)) > + return false; > + return true; > } > > /* > @@ -2825,7 +2836,8 @@ int __do_munmap(struct mm_struct *mm, unsigned long start, size_t len, > } > > /* Detach vmas from rbtree */ > - detach_vmas_to_be_unmapped(mm, vma, prev, end); > + if (!detach_vmas_to_be_unmapped(mm, vma, prev, end)) > + downgrade = false; > > if (downgrade) > mmap_write_downgrade(mm); >