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[209.132.183.28]) by mx.google.com with ESMTPS id p18si2024698qtc.229.2019.02.25.23.20.42 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 25 Feb 2019 23:20:42 -0800 (PST) Received-SPF: pass (google.com: domain of peterx@redhat.com designates 209.132.183.28 as permitted sender) client-ip=209.132.183.28; Authentication-Results: mx.google.com; spf=pass (google.com: domain of peterx@redhat.com designates 209.132.183.28 as permitted sender) smtp.mailfrom=peterx@redhat.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 000A0309705F; Tue, 26 Feb 2019 07:20:40 +0000 (UTC) Received: from xz-x1 (dhcp-14-116.nay.redhat.com [10.66.14.116]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 5F8BB5C6B8; Tue, 26 Feb 2019 07:20:30 +0000 (UTC) Date: Tue, 26 Feb 2019 15:20:28 +0800 From: Peter Xu To: Mike Rapoport Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, David Hildenbrand , Hugh Dickins , Maya Gokhale , Jerome Glisse , Pavel Emelyanov , Johannes Weiner , Martin Cracauer , Shaohua Li , Marty McFadden , Andrea Arcangeli , Mike Kravetz , Denis Plotnikov , Mike Rapoport , Mel Gorman , "Kirill A . Shutemov" , "Dr . David Alan Gilbert" , Rik van Riel Subject: Re: [PATCH v2 20/26] userfaultfd: wp: support write protection for userfault vma range Message-ID: <20190226072027.GK13653@xz-x1> References: <20190212025632.28946-1-peterx@redhat.com> <20190212025632.28946-21-peterx@redhat.com> <20190225205233.GC10454@rapoport-lnx> <20190226060627.GG13653@xz-x1> <20190226064347.GB5873@rapoport-lnx> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20190226064347.GB5873@rapoport-lnx> User-Agent: Mutt/1.10.1 (2018-07-13) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.43]); Tue, 26 Feb 2019 07:20:41 +0000 (UTC) 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 Tue, Feb 26, 2019 at 08:43:47AM +0200, Mike Rapoport wrote: > On Tue, Feb 26, 2019 at 02:06:27PM +0800, Peter Xu wrote: > > On Mon, Feb 25, 2019 at 10:52:34PM +0200, Mike Rapoport wrote: > > > On Tue, Feb 12, 2019 at 10:56:26AM +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: 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 > > > > [peterx: > > > > - use the helper to find VMA; > > > > - return -ENOENT if not found to match mcopy case; > > > > - use the new MM_CP_UFFD_WP* flags for change_protection > > > > - check against mmap_changing for failures] > > > > Signed-off-by: Peter Xu > > > > --- > > > > include/linux/userfaultfd_k.h | 3 ++ > > > > mm/userfaultfd.c | 54 +++++++++++++++++++++++++++++++++++ > > > > 2 files changed, 57 insertions(+) > > > > > > > > diff --git a/include/linux/userfaultfd_k.h b/include/linux/userfaultfd_k.h > > > > index 765ce884cec0..8f6e6ed544fb 100644 > > > > --- a/include/linux/userfaultfd_k.h > > > > +++ b/include/linux/userfaultfd_k.h > > > > @@ -39,6 +39,9 @@ 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, bool *mmap_changing); > > > > > > > > /* 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 fefa81c301b7..529d180bb4d7 100644 > > > > --- a/mm/userfaultfd.c > > > > +++ b/mm/userfaultfd.c > > > > @@ -639,3 +639,57 @@ ssize_t mfill_zeropage(struct mm_struct *dst_mm, unsigned long start, > > > > { > > > > return __mcopy_atomic(dst_mm, start, 0, len, true, mmap_changing, 0); > > > > } > > > > + > > > > +int mwriteprotect_range(struct mm_struct *dst_mm, unsigned long start, > > > > + unsigned long len, bool enable_wp, bool *mmap_changing) > > > > +{ > > > > + 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); > > > > > > I'd replace these BUG_ON()s with > > > > > > if (WARN_ON()) > > > return -EINVAL; > > > > I believe BUG_ON() is used because these parameters should have been > > checked in userfaultfd_writeprotect() already by the common > > validate_range() even before calling mwriteprotect_range(). So I'm > > fine with the WARN_ON() approach but I'd slightly prefer to simply > > keep the patch as is to keep Jerome's r-b if you won't disagree. :) > > Right, userfaultfd_writeprotect() should check these parameters and if it > didn't it was a bug indeed. But still, it's not severe enough to crash the > kernel. > > I hope Jerome wouldn't mind to keep his r-b with s/BUG_ON/WARN_ON ;-) > > With this change you can also add > > Reviewed-by: Mike Rapoport Thanks! Though before I change anything... please note that the BUG_ON()s are really what we've done in existing MISSING code. One example is userfaultfd_copy() which did validate_range() first, then in __mcopy_atomic() we've used BUG_ON()s. They make sense to me becauase userspace should never be able to trigger it. And if we really want to change the BUG_ON()s in this patch, IMHO we probably want to change the other BUG_ON()s as well, then that can be a standalone patch or patchset to address another issue... (and if we really want to use WARN_ON, I would prefer WARN_ON_ONCE, or directly return the errors to avoid DOS). I'll see how you'd prefer to see how I should move on with this patch. Thanks, -- Peter Xu