From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jerome Glisse Subject: Re: [PATCH 2/5] drm/radeon: add userptr flag to limit it to anonymous memory v2 Date: Wed, 6 Aug 2014 23:45:48 -0400 Message-ID: <20140807034547.GA7046@gmail.com> References: <1407254732-8332-1-git-send-email-deathsimple@vodafone.de> <1407254732-8332-2-git-send-email-deathsimple@vodafone.de> <20140805173932.GA2854@gmail.com> <53E11831.1010809@vodafone.de> <20140805221334.GA3991@gmail.com> <53E1D160.4040804@vodafone.de> <20140806160847.GA3142@gmail.com> <53E26325.8070309@vodafone.de> <20140806183415.GA4716@gmail.com> <20140806202431.GW8727@phenom.ffwll.local> Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Return-path: Received: from mail-qa0-f46.google.com (mail-qa0-f46.google.com [209.85.216.46]) by gabe.freedesktop.org (Postfix) with ESMTP id D4A226E0D0 for ; Wed, 6 Aug 2014 20:45:45 -0700 (PDT) Received: by mail-qa0-f46.google.com with SMTP id v10so3461683qac.5 for ; Wed, 06 Aug 2014 20:45:45 -0700 (PDT) Content-Disposition: inline In-Reply-To: <20140806202431.GW8727@phenom.ffwll.local> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" To: Daniel Vetter Cc: dri-devel@lists.freedesktop.org List-Id: dri-devel@lists.freedesktop.org On Wed, Aug 06, 2014 at 10:24:31PM +0200, Daniel Vetter wrote: > On Wed, Aug 06, 2014 at 02:34:16PM -0400, Jerome Glisse wrote: > > On Wed, Aug 06, 2014 at 07:17:25PM +0200, Christian K=F6nig wrote: > > > Am 06.08.2014 um 18:08 schrieb Jerome Glisse: > > > >On Wed, Aug 06, 2014 at 08:55:28AM +0200, Christian K=F6nig wrote: > > > >>Am 06.08.2014 um 00:13 schrieb Jerome Glisse: > > > >>>On Tue, Aug 05, 2014 at 07:45:21PM +0200, Christian K=F6nig wrote: > > > >>>>Am 05.08.2014 um 19:39 schrieb Jerome Glisse: > > > >>>>>On Tue, Aug 05, 2014 at 06:05:29PM +0200, Christian K=F6nig wrot= e: > > > >>>>>>From: Christian K=F6nig > > > >>>>>> > > > >>>>>>Avoid problems with writeback by limiting userptr to anonymous = memory. > > > >>>>>> > > > >>>>>>v2: add commit and code comments > > > >>>>>I guess, i have not expressed myself clearly. This is bogus, you= pretend > > > >>>>>you want to avoid writeback issue but you still allow userspace = to map > > > >>>>>file backed pages (which by the way might be a regular bo object= from > > > >>>>>another device for instance and that would be fun). > > > >>>>> > > > >>>>>So this patch is a no go and i would rather see that this userpt= r to > > > >>>>>be restricted to anon vma only no matter what. No flags here. > > > >>>>Mapping of non anonymous memory (e.g. everything get_user_pages w= on't fail > > > >>>>with) is restricted to read only access by the GPU. > > > >>>> > > > >>>>I'm fine with making it a hard requirement for all mappings if yo= u say it's > > > >>>>a must have. > > > >>>> > > > >>>Well for time being you should force read only. The way you implem= ent write > > > >>>is broken. Here is how it can abuse to allow write to a file backe= d mmap. > > > >>> > > > >>>mmap(fixaddress,fixedsize,NOFD) > > > >>>userptr_ioctl(fixedaddress, RADEON_GEM_USERPTR_ANONONLY) > > > >>>// bo is created successfully because fixedaddress is part of anon= vma > > > >>>munmap(fixedaddress,fixedsize) > > > >>>// radeon get mmu_notifier_range_start callback and unbind page fr= om the > > > >>>// bo but radeon does not know there was an unmap. > > > >>>mmap(fixaddress,fixedsize,fd_to_this_read_only_file_i_want_to_writ= e_to) > > > >>>radeon_ioctl_use_my_userptrbo > > > >>>// bo is bind again by radeon and because all flag are set at crea= tion > > > >>>// it is map with write permission allowing someone to write to a = file > > > >>>// that might be read only for the user. > > > >>>// > > > >>>// Script kiddies it's time to learn about gpu ... > > > >>> > > > >>>Of course if you this patch (kind of selling my own junk here) : > > > >>> > > > >>>http://www.spinics.net/lists/linux-mm/msg75878.html > > > >>> > > > >>>then you could know inside the range_start that you should remove = the > > > >>>write permission and that it should be rechecked on next bind. > > > >>> > > > >>>Note that i have not read much of your code so maybe you handle th= is > > > >>>case somehow. > > > >>I've stumbled over this attack vector as well and it's the reason w= hy I've > > > >>moved checking the access rights to the bind callback instead of BO= creation > > > >>time with V5 of the patch. > > > >> > > > >>This way you get an -EFAULT if you try something like this on comma= nd > > > >>submission time. > > > >So you seem immune to that issue but you are still not checking if t= he anon > > > >vma is writeable which you should again security concern here. > > > = > > > We check the access rights of the pointer using: > > > > if (!access_ok(write ? VERIFY_WRITE : VERIFY_READ, > > > >(long)gtt->userptr, > > > > ttm->num_pages * PAGE_SIZE)) > > > > return -EFAULT; > > > = > > > Shouldn't that be enough? > > = > > No, access_ok only check against special area on some architecture and = i am > > pretty sure on x86 the VERIFY_WRITE or VERIFY_READ is just flat out ign= ored. > > = > > What you need to test is the vma vm_flags somethings like > > = > > if (write && !(vma->vm_flags VM_WRITE)) > > return -EPERM; > > = > > Which need to happen on all bind. > = > access_ok is _only_ valid in combination with copy_from/to_user and > friends and is an optimization of the access checks depending upon > architecture. You always need them both, one alone is useless. ENOPARSE, access_ok will always return the same value for a given address a= t least on x86 so if address supplied at ioctl time is a valid userspace address th= en it will still be a valid userspace address at buffer object bind time (note th= at the user address is immutable here). So access_ok can be done once and only onc= e inside the ioctl and then for the write permission you need to recheck the vma eac= h time you bind the object (or rather each time the previous bind was invalidated = by some mmu_notifier call). That being said access_ok is kind of useless given that get_user_page will = fail on kernel address and i assume for any special address any architecture might = have. So strictly speaking the access_ok is just a way to fail early and flatout ins= tead of delaying the failure to bind time. Or do i need to go read x86 code again ? Cheers, J=E9r=F4me > -Daniel > -- = > Daniel Vetter > Software Engineer, Intel Corporation > +41 (0) 79 365 57 48 - http://blog.ffwll.ch