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 12:08:49 -0400 Message-ID: <20140806160847.GA3142@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> Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Return-path: Received: from mail-qa0-f45.google.com (mail-qa0-f45.google.com [209.85.216.45]) by gabe.freedesktop.org (Postfix) with ESMTP id 8F60A6E28C for ; Wed, 6 Aug 2014 09:08:47 -0700 (PDT) Received: by mail-qa0-f45.google.com with SMTP id cm18so2613777qab.32 for ; Wed, 06 Aug 2014 09:08:46 -0700 (PDT) Content-Disposition: inline In-Reply-To: <53E1D160.4040804@vodafone.de> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" To: Christian =?iso-8859-1?Q?K=F6nig?= Cc: dri-devel@lists.freedesktop.org List-Id: dri-devel@lists.freedesktop.org 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 wrote: > >>>>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 prete= nd > >>>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 userptr to > >>>be restricted to anon vma only no matter what. No flags here. > >>Mapping of non anonymous memory (e.g. everything get_user_pages won't f= ail > >>with) is restricted to read only access by the GPU. > >> > >>I'm fine with making it a hard requirement for all mappings if you say = it's > >>a must have. > >> > >Well for time being you should force read only. The way you implement wr= ite > >is broken. Here is how it can abuse to allow write to a file backed mmap. > > > >mmap(fixaddress,fixedsize,NOFD) > >userptr_ioctl(fixedaddress, RADEON_GEM_USERPTR_ANONONLY) > >// bo is created successfully because fixedaddress is part of anonvma > >munmap(fixedaddress,fixedsize) > >// radeon get mmu_notifier_range_start callback and unbind page from the > >// bo but radeon does not know there was an unmap. > >mmap(fixaddress,fixedsize,fd_to_this_read_only_file_i_want_to_write_to) > >radeon_ioctl_use_my_userptrbo > >// bo is bind again by radeon and because all flag are set at creation > >// 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 this > >case somehow. > = > I've stumbled over this attack vector as well and it's the reason why I've > moved checking the access rights to the bind callback instead of BO creat= ion > time with V5 of the patch. > = > This way you get an -EFAULT if you try something like this on command > submission time. So you seem immune to that issue but you are still not checking if the anon vma is writeable which you should again security concern here. Cheers, J=E9r=F4me