From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pl1-f200.google.com (mail-pl1-f200.google.com [209.85.214.200]) by kanga.kvack.org (Postfix) with ESMTP id 438A18E0001 for ; Mon, 21 Jan 2019 05:20:50 -0500 (EST) Received: by mail-pl1-f200.google.com with SMTP id a9so12938426pla.2 for ; Mon, 21 Jan 2019 02:20:50 -0800 (PST) Received: from mx0a-001b2d01.pphosted.com (mx0a-001b2d01.pphosted.com. [148.163.156.1]) by mx.google.com with ESMTPS id v34si11832901plg.205.2019.01.21.02.20.48 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 21 Jan 2019 02:20:49 -0800 (PST) Received: from pps.filterd (m0098404.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.27/8.16.0.27) with SMTP id x0LADtjo110482 for ; Mon, 21 Jan 2019 05:20:48 -0500 Received: from e06smtp07.uk.ibm.com (e06smtp07.uk.ibm.com [195.75.94.103]) by mx0a-001b2d01.pphosted.com with ESMTP id 2q5b92tqap-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Mon, 21 Jan 2019 05:20:48 -0500 Received: from localhost by e06smtp07.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Mon, 21 Jan 2019 10:20:45 -0000 Date: Mon, 21 Jan 2019 12:20:35 +0200 From: Mike Rapoport Subject: Re: [PATCH RFC 06/24] userfaultfd: wp: support write protection for userfault vma range References: <20190121075722.7945-1-peterx@redhat.com> <20190121075722.7945-7-peterx@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190121075722.7945-7-peterx@redhat.com> Message-Id: <20190121102035.GC19725@rapoport-lnx> Sender: owner-linux-mm@kvack.org List-ID: To: Peter Xu Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Hugh Dickins , Maya Gokhale , Jerome Glisse , Johannes Weiner , Martin Cracauer , Denis Plotnikov , Shaohua Li , Andrea Arcangeli , Pavel Emelyanov , Mike Kravetz , Marty McFadden , Mike Rapoport , Mel Gorman , "Kirill A . Shutemov" , "Dr . David Alan Gilbert" , Rik van Riel On Mon, Jan 21, 2019 at 03:57:04PM +0800, Peter Xu wrote: > From: Shaohua Li > > Add API to enable/disable writeprotect a vma range. Unlike mprotect, > this doesn't split/merge vmas. > > Cc: Andrea Arcangeli > Cc: Pavel Emelyanov > Cc: Rik van Riel > Cc: Kirill A. Shutemov > Cc: Mel Gorman > Cc: Hugh Dickins > Cc: Johannes Weiner > Signed-off-by: Shaohua Li > Signed-off-by: Andrea Arcangeli > Signed-off-by: Peter Xu > --- > include/linux/userfaultfd_k.h | 2 ++ > mm/userfaultfd.c | 52 +++++++++++++++++++++++++++++++++++ > 2 files changed, 54 insertions(+) > > diff --git a/include/linux/userfaultfd_k.h b/include/linux/userfaultfd_k.h > index 38f748e7186e..e82f3156f4e9 100644 > --- a/include/linux/userfaultfd_k.h > +++ b/include/linux/userfaultfd_k.h > @@ -37,6 +37,8 @@ extern ssize_t mfill_zeropage(struct mm_struct *dst_mm, > unsigned long dst_start, > unsigned long len, > bool *mmap_changing); > +extern int mwriteprotect_range(struct mm_struct *dst_mm, > + unsigned long start, unsigned long len, bool enable_wp); > > /* mm helpers */ > static inline bool is_mergeable_vm_userfaultfd_ctx(struct vm_area_struct *vma, > diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c > index 458acda96f20..c38903f501c7 100644 > --- a/mm/userfaultfd.c > +++ b/mm/userfaultfd.c > @@ -615,3 +615,55 @@ ssize_t mfill_zeropage(struct mm_struct *dst_mm, unsigned long start, > { > return __mcopy_atomic(dst_mm, start, 0, len, true, mmap_changing); > } > + > +int mwriteprotect_range(struct mm_struct *dst_mm, unsigned long start, > + unsigned long len, bool enable_wp) > +{ > + struct vm_area_struct *dst_vma; > + pgprot_t newprot; > + int err; > + > + /* > + * Sanitize the command parameters: > + */ > + BUG_ON(start & ~PAGE_MASK); > + BUG_ON(len & ~PAGE_MASK); > + > + /* Does the address range wrap, or is the span zero-sized? */ > + BUG_ON(start + len <= start); > + > + down_read(&dst_mm->mmap_sem); > + > + /* > + * Make sure the vma is not shared, that the dst range is > + * both valid and fully within a single existing vma. > + */ > + err = -EINVAL; In non-cooperative mode, there can be a race between VM layout changes and mcopy_atomic [1]. I believe the same races are possible here, so can we please make err = -ENOENT for consistency with mcopy? > + dst_vma = find_vma(dst_mm, start); > + if (!dst_vma || (dst_vma->vm_flags & VM_SHARED)) > + goto out_unlock; > + if (start < dst_vma->vm_start || > + start + len > dst_vma->vm_end) > + goto out_unlock; > + > + if (!dst_vma->vm_userfaultfd_ctx.ctx) > + goto out_unlock; > + if (!userfaultfd_wp(dst_vma)) > + goto out_unlock; > + > + if (!vma_is_anonymous(dst_vma)) > + goto out_unlock; The sanity checks here seem to repeat those in mcopy_atomic(). I'd suggest splitting them out to a helper function. > + if (enable_wp) > + newprot = vm_get_page_prot(dst_vma->vm_flags & ~(VM_WRITE)); > + else > + newprot = vm_get_page_prot(dst_vma->vm_flags); > + > + change_protection(dst_vma, start, start + len, newprot, > + !enable_wp, 0); > + > + err = 0; > +out_unlock: > + up_read(&dst_mm->mmap_sem); > + return err; > +} > -- > 2.17.1 [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=27d02568f529e908399514dfbee8ee43bdfd5299 -- Sincerely yours, Mike.