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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Tue, 26 Feb 2019 07:46:16 -0000 Received: from d06av26.portsmouth.uk.ibm.com (d06av26.portsmouth.uk.ibm.com [9.149.105.62]) by b06cxnps3075.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id x1Q7kFvv59703536 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=FAIL); Tue, 26 Feb 2019 07:46:15 GMT Received: from d06av26.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id B7B55AE045; Tue, 26 Feb 2019 07:46:15 +0000 (GMT) Received: from d06av26.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 459F6AE053; Tue, 26 Feb 2019 07:46:14 +0000 (GMT) Received: from rapoport-lnx (unknown [9.148.8.84]) by d06av26.portsmouth.uk.ibm.com (Postfix) with ESMTPS; Tue, 26 Feb 2019 07:46:14 +0000 (GMT) Date: Tue, 26 Feb 2019 09:46:12 +0200 From: Mike Rapoport To: Peter Xu 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 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> <20190226072027.GK13653@xz-x1> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190226072027.GK13653@xz-x1> User-Agent: Mutt/1.5.24 (2015-08-30) X-TM-AS-GCONF: 00 x-cbid: 19022607-4275-0000-0000-000003140664 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19022607-4276-0000-0000-0000382244BC Message-Id: <20190226074612.GG5873@rapoport-lnx> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-02-26_06:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1902260059 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Feb 26, 2019 at 03:20:28PM +0800, Peter Xu wrote: > 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... Yeah, we have quite a lot of them, so doing the replacement in a separate patch makes perfect sense. > (and if we really want to use WARN_ON, I would prefer WARN_ON_ONCE, or > directly return the errors to avoid DOS). Agree. > I'll see how you'd prefer to see how I should move on with this patch. Let's keep this patch as is and make the replacement on top of the WP series. Feel free to add r-b. > Thanks, > > -- > Peter Xu > -- Sincerely yours, Mike.