On Thu, Sep 20, 2018 at 10:23:40AM -0400, Jerome Glisse wrote: > Received: from popscn.huawei.com [10.3.17.45] by Turing-Arch-b with POP3 > (fetchmail-6.3.26) for <kenny@localhost> (single-drop); Thu, 20 Sep 2018 > 22:30:01 +0800 (CST) > Received: from DGGEMM401-HUB.china.huawei.com (10.3.20.209) by > dggeml405-hub.china.huawei.com (10.3.17.49) with Microsoft SMTP Server > (TLS) id 14.3.382.0; Thu, 20 Sep 2018 22:23:57 +0800 > Received: from dggwg01-in.huawei.com (172.30.65.35) by > DGGEMM401-HUB.china.huawei.com (10.3.20.209) with Microsoft SMTP Server id > 14.3.399.0; Thu, 20 Sep 2018 22:23:56 +0800 > Received: from mx1.redhat.com (unknown [209.132.183.28]) by Forcepoint > Email with ESMTPS id 18963FA9B6FA9; Thu, 20 Sep 2018 22:23:50 +0800 (CST) > Received: from smtp.corp.redhat.com > (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using > TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client > certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id > CF1D9C058CBE; Thu, 20 Sep 2018 14:23:47 +0000 (UTC) > Received: from redhat.com (unknown [10.20.6.215]) by > smtp.corp.redhat.com (Postfix) with ESMTPS id 1B030106A780; Thu, 20 Sep > 2018 14:23:41 +0000 (UTC) > Date: Thu, 20 Sep 2018 10:23:40 -0400 > From: Jerome Glisse <jglisse@xxxxxxxxxx> > To: Kenneth Lee <liguozhu@xxxxxxxxxxxxx> > CC: Kenneth Lee <nek.in.cn@xxxxxxxxx>, Alex Williamson > <alex.williamson@xxxxxxxxxx>, Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>, > kvm@xxxxxxxxxxxxxxx, Jonathan Corbet <corbet@xxxxxxx>, Greg Kroah-Hartman > <gregkh@xxxxxxxxxxxxxxxxxxx>, Joerg Roedel <joro@xxxxxxxxxx>, > linux-doc@xxxxxxxxxxxxxxx, Sanjay Kumar <sanjay.k.kumar@xxxxxxxxx>, Hao > Fang <fanghao11@xxxxxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx, > linuxarm@xxxxxxxxxx, iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx, "David S . Miller" > <davem@xxxxxxxxxxxxx>, linux-crypto@xxxxxxxxxxxxxxx, Zhou Wang > <wangzhou1@xxxxxxxxxxxxx>, Philippe Ombredanne <pombredanne@xxxxxxxx>, > Thomas Gleixner <tglx@xxxxxxxxxxxxx>, Zaibo Xu <xuzaibo@xxxxxxxxxx>, > linux-accelerators@xxxxxxxxxxxxxxxx, Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx> > Subject: Re: [RFCv2 PATCH 0/7] A General Accelerator Framework, WarpDrive > Message-ID: <20180920142340.GA3341@xxxxxxxxxx> > References: <20180903005204.26041-1-nek.in.cn@xxxxxxxxx> > <20180917014244.GA27596@xxxxxxxxxx> > <20180917083940.GE207969@Turing-Arch-b> <20180917123744.GA3605@xxxxxxxxxx> > <20180918060014.GF207969@Turing-Arch-b> <20180918130314.GA3500@xxxxxxxxxx> > <20180920055543.GG207969@Turing-Arch-b> > Content-Type: text/plain; charset="iso-8859-1" > Content-Disposition: inline > Content-Transfer-Encoding: 8bit > In-Reply-To: <20180920055543.GG207969@Turing-Arch-b> > User-Agent: Mutt/1.10.0 (2018-05-17) > X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 > X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 > (mx1.redhat.com [10.5.110.32]); Thu, 20 Sep 2018 14:23:48 +0000 (UTC) > Return-Path: jglisse@xxxxxxxxxx > X-MS-Exchange-Organization-AuthSource: DGGEMM401-HUB.china.huawei.com > X-MS-Exchange-Organization-AuthAs: Anonymous > MIME-Version: 1.0 > > On Thu, Sep 20, 2018 at 01:55:43PM +0800, Kenneth Lee wrote: > > On Tue, Sep 18, 2018 at 09:03:14AM -0400, Jerome Glisse wrote: > > > On Tue, Sep 18, 2018 at 02:00:14PM +0800, Kenneth Lee wrote: > > > > On Mon, Sep 17, 2018 at 08:37:45AM -0400, Jerome Glisse wrote: > > > > > On Mon, Sep 17, 2018 at 04:39:40PM +0800, Kenneth Lee wrote: > > > > > > On Sun, Sep 16, 2018 at 09:42:44PM -0400, Jerome Glisse wrote: > > > > > > > So i want to summarize issues i have as this threads have dig deep into > > > > > > > details. For this i would like to differentiate two cases first the easy > > > > > > > one when relying on SVA/SVM. Then the second one when there is no SVA/SVM. > > > > > > > > > > > > Thank you very much for the summary. > > > > > > > > > > > > > In both cases your objectives as i understand them: > > > > > > > > > > > > > > [R1]- expose a common user space API that make it easy to share boiler > > > > > > > plate code accross many devices (discovering devices, opening > > > > > > > device, creating context, creating command queue ...). > > > > > > > [R2]- try to share the device as much as possible up to device limits > > > > > > > (number of independant queues the device has) > > > > > > > [R3]- minimize syscall by allowing user space to directly schedule on the > > > > > > > device queue without a round trip to the kernel > > > > > > > > > > > > > > I don't think i missed any. > > > > > > > > > > > > > > > > > > > > > (1) Device with SVA/SVM > > > > > > > > > > > > > > For that case it is easy, you do not need to be in VFIO or part of any > > > > > > > thing specific in the kernel. There is no security risk (modulo bug in > > > > > > > the SVA/SVM silicon). Fork/exec is properly handle and binding a process > > > > > > > to a device is just couple dozen lines of code. > > > > > > > > > > > > > > > > > > > This is right...logically. But the kernel has no clear definition about "Device > > > > > > with SVA/SVM" and no boiler plate for doing so. Then VFIO may become one of the > > > > > > boiler plate. > > > > > > > > > > > > VFIO is one of the wrappers for IOMMU for user space. And maybe it is the only > > > > > > one. If we add that support within VFIO, which solve most of the problem of > > > > > > SVA/SVM, it will save a lot of work in the future. > > > > > > > > > > You do not need to "wrap" IOMMU for SVA/SVM. Existing upstream SVA/SVM user > > > > > all do the SVA/SVM setup in couple dozen lines and i failed to see how it > > > > > would require any more than that in your case. > > > > > > > > > > > > > > > > I think this is the key confliction between us. So could Alex please say > > > > > > something here? If the VFIO is going to take this into its scope, we can try > > > > > > together to solve all the problem on the way. If it it is not, it is also > > > > > > simple, we can just go to another way to fulfill this part of requirements even > > > > > > we have to duplicate most of the code. > > > > > > > > > > > > Another point I need to emphasis here: because we have to replace the hardware > > > > > > queue when fork, so it won't be very simple even in SVA/SVM case. > > > > > > > > > > I am assuming hardware queue can only be setup by the kernel and thus > > > > > you are totaly safe forkwise as the queue is setup against a PASID and > > > > > the child does not bind to any PASID and you use VM_DONTCOPY on the > > > > > mmap of the hardware MMIO queue because you should really use that flag > > > > > for that. > > > > > > > > > > > > > > > > > (2) Device does not have SVA/SVM (or it is disabled) > > > > > > > > > > > > > > You want to still allow device to be part of your framework. However > > > > > > > here i see fundamentals securities issues and you move the burden of > > > > > > > being careful to user space which i think is a bad idea. We should > > > > > > > never trus the userspace from kernel space. > > > > > > > > > > > > > > To keep the same API for the user space code you want a 1:1 mapping > > > > > > > between device physical address and process virtual address (ie if > > > > > > > device access device physical address A it is accessing the same > > > > > > > memory as what is backing the virtual address A in the process. > > > > > > > > > > > > > > Security issues are on two things: > > > > > > > [I1]- fork/exec, a process who opened any such device and created an > > > > > > > active queue can transfer without its knowledge control of its > > > > > > > commands queue through COW. The parent map some anonymous region > > > > > > > to the device as a command queue buffer but because of COW the > > > > > > > parent can be the first to copy on write and thus the child can > > > > > > > inherit the original pages that are mapped to the hardware. > > > > > > > Here parent lose control and child gain it. > > > > > > > > > > > > This is indeed an issue. But it remains an issue only if you continue to use the > > > > > > queue and the memory after fork. We can use at_fork kinds of gadget to fix it in > > > > > > user space. > > > > > > > > > > Trusting user space is a no go from my point of view. > > > > > > > > Can we dive deeper on this? Maybe we have different understanding on "Trusting > > > > user space". As my understanding, "trusting user space" means "no matter what > > > > the user process does, it should only hurt itself and anything give to it, no > > > > the kernel and the other process". > > > > > > > > In our case, we create a channel between a process and the hardware. The process > > > > can do whateven it like to its own memory the channel itself. It won't hurt the > > > > other process and the kernel. And if the process fork a child and give the > > > > channel to the child, it should the freedom on those resource remain within the > > > > parent and the child. We are not trust another else. > > > > > > > > So do you refer to something else here? > > > > > > > > > > I am refering to COW giving control to the child on to what happens > > > in the parent from device point of view. A process hurting itself is > > > fine, but if process now has to do special steps to protect from > > > its child ie make sure that its childs can not hurt it, then i see > > > that as a kernel bug. We can not ask user space process to know about > > > all the thousands things that needs to be done to avoid issues with > > > each device driver that the process may use (process can be totaly > > > ignorant it is using a device if that device is use by a library it > > > links to). > > > > > > > > > Maybe what needs to happen will explain it better. So if userspace > > > wants to be secure and protect itself from its child taking over the > > > device through COW: > > > > > > - parent opened a device and is using it > > > > > > ... when parent wants to fork/exec it must: > > > > > > - parent _must_ flush device command queue and wait for the > > > device to finish all pending jobs > > > > > > - parent _must_ unmap all range mapped to the device > > > > > > - parent should first close device file (unless you force set > > > the CLOEXEC flag in the kernel)/it could also just flush > > > but if you are not mapping the device command queue with > > > VM_DONTCOPY then you should really be closing the device > > > > > > - now parent can fork/exec > > > > > > - parent must force COW ie write at least one byte to _all_ > > > pages in the range it wants to use with the device > > > > > > - parent re-open the device and re-initialize everything > > > > > > > > > So this is putting quite a burden on a number of steps the parent > > > _must_ do in order to keep control of memory exposed to the device. > > > Not doing so can potentialy lead (it depends on who does the COW > > > first) to the child taking control of memory use by the device, > > > memory which was mapped by the parent before the child was created. > > > > > > Forcing CLOEXEC and VM_DONTCOPY somewhat help to simplify this, > > > but you still need to stop, flush, unmap, before fork/exec and then > > > re-init everything after. > > > > > > > > > This is only when not using SVA/SVM, SVA/SVM is totaly fine from > > > that point of view, no issues whatsoever. > > > > > > The solution i outlined in previous email do not have that above > > > issue either, no need to rely on user space doing that dance. > > > > Thank you. I get the point. I'm now trying to see if I can solve the problem by > > seting the vma to VM_SHARED when the portiong is "shared to the hardware". > > > > FYI you can not convert a private anonymous vma to a share one it is > illegal AFAIK at least i never heard of it and i am pretty sure the > mm code would break if that happens. The user space is the one that > decide what flags a vma has, not the kernel. Modulo few flags like > DONTCOPY that can be force set by device driver for their vma ie vma > of an mmap against the device file. > > If you don't like my solution here is another one but it is ugly and > i think it is a bad idea. Again this is for the non SVA/SVM case and > it assumes that the command queue is a mmap() of the device file: > (A) register mmu_notifier > (B) on _every_ invalidate range callback (_no matter_ what is the > range) you zap the command queue mapped to user space (this is > because you can't tell if the callback happens for a fork or > something else) wait for the hardware queue to finish and clear > all the iommu/dma mapping and you unpin all the pages ie > put_page() > (C) in device file vma page fault handler (vm_operations_struct. > fault) you redo all the GUP and redo all the iommu/dma mapping > and you remap the command queue to the userspace > > In (C) you can remap different command queue if you are in the child > than in the parent (just look at current->mm and compare it to the > one the command queue was created against). > > Note that this solution will be much __slower__ than what i described > in my previous email. You will see that mmu notifier callbacks happens > often and for tons of reasons and you will be _constantly_ undoing and > redoing tons of work. > > This can be mitigated if you can differentiate reasons behind a mmu > notifier callback. I posted patchset to do that a while ago and i > intend to post it again in the next month or so. But this would still > be a bad idea and solution i described previously is much more sane. > > Trying to pretend you can have the same thing as SVA/SVM without SVA > is not a good idea. The non SVA case can still expose same API (like > i described previously) but should go through kernel for _every_ > hardware submission (you can batch multiple commands in one submission). > Not doing so is way too risky from my POV. > > Cheers, > Jérôme You are quite right. I tried all the way to find a leak in the mm system and fail to. I will tried other way or maybe discard the non-SVA scenario. Cheers, -- -Kenneth(Hisilicon)
