From: Lu Baolu <baolu.lu@linux.intel.com>
To: Bjorn Helgaas <helgaas@kernel.org>
Cc: baolu.lu@linux.intel.com,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Joerg Roedel <joro@8bytes.org>,
Alex Williamson <alex.williamson@redhat.com>,
Bjorn Helgaas <bhelgaas@google.com>,
Jason Gunthorpe <jgg@nvidia.com>,
Christoph Hellwig <hch@infradead.org>,
Kevin Tian <kevin.tian@intel.com>,
Ashok Raj <ashok.raj@intel.com>, Will Deacon <will@kernel.org>,
Robin Murphy <robin.murphy@arm.com>,
Dan Williams <dan.j.williams@intel.com>,
rafael@kernel.org, Diana Craciun <diana.craciun@oss.nxp.com>,
Cornelia Huck <cohuck@redhat.com>,
Eric Auger <eric.auger@redhat.com>, Liu Yi L <yi.l.liu@intel.com>,
Jacob jun Pan <jacob.jun.pan@intel.com>,
Chaitanya Kulkarni <kch@nvidia.com>,
Stuart Yoder <stuyoder@gmail.com>,
Laurentiu Tudor <laurentiu.tudor@nxp.com>,
Thierry Reding <thierry.reding@gmail.com>,
David Airlie <airlied@linux.ie>, Daniel Vetter <daniel@ffwll.ch>,
Jonathan Hunter <jonathanh@nvidia.com>,
Li Yang <leoyang.li@nxp.com>, Dmitry Osipenko <digetx@gmail.com>,
iommu@lists.linux-foundation.org, linux-pci@vger.kernel.org,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v4 04/13] PCI: portdrv: Suppress kernel DMA ownership auto-claiming
Date: Thu, 30 Dec 2021 13:49:53 +0800 [thread overview]
Message-ID: <1af0f6c6-c39b-c018-3ca1-20e778cb926b@linux.intel.com> (raw)
In-Reply-To: <20211229211626.GA1701512@bhelgaas>
Hi Bjorn,
On 12/30/21 5:16 AM, Bjorn Helgaas wrote:
> On Fri, Dec 17, 2021 at 02:36:59PM +0800, Lu Baolu wrote:
>> IOMMU grouping on PCI necessitates that if we lack isolation on a bridge
>> then all of the downstream devices will be part of the same IOMMU group
>> as the bridge. The existing vfio framework allows the portdrv driver to
>> be bound to the bridge while its downstream devices are assigned to user
>> space. The pci_dma_configure() marks the iommu_group as containing only
>> devices with kernel drivers that manage DMA. Avoid this default behavior
>> for the portdrv driver in order for compatibility with the current vfio
>> policy.
>
> A word about the isolation would be useful. I think you're referring
> to some specific ACS controls, probably P2P Request Redirect?
>
> I guess this is just a wording issue, but I think it's actually the
> *lack* of some ACS controls that forces us to put several devices in
> the same IOMMU group, isn't it? It's not that we start with "IOMMU
> grouping" and that necessitates something else.
>
> Maybe something like this?
>
> If a switch lacks ACS P2P Request Redirect (and possibly other
> controls?), a device below the switch can bypass the IOMMU and DMA
> directly to other devices below the switch, so all the downstream
> devices must be in the same IOMMU group as the switch itself.
Yes. That's what it means from the perspective of PCI/PCIe. I will use
this in the next version. Thanks!
>
>> The commit 5f096b14d421b ("vfio: Whitelist PCI bridges") extended above
>> policy to all kernel drivers of bridge class. This is not always safe.
>> For example, The shpchp_core driver relies on the PCI MMIO access for the
>> controller functionality. With its downstream devices assigned to the
>> userspace, the MMIO might be changed through user initiated P2P accesses
>> without any notification. This might break the kernel driver integrity
>> and lead to some unpredictable consequences.
>>
>> For any bridge driver, in order to avoiding default kernel DMA ownership
>> claiming, we should consider:
>>
>> 1) Does the bridge driver use DMA? Calling pci_set_master() or
>> a dma_map_* API is a sure indicate the driver is doing DMA
>>
>> 2) If the bridge driver uses MMIO, is it tolerant to hostile
>> userspace also touching the same MMIO registers via P2P DMA
>> attacks?
>>
>> Conservatively if the driver maps an MMIO region at all, we can say that
>> it fails the test.
>
> I'm not sure what all this explanation is telling me. It says
> something done by 5f096b14d421 is not always safe, but this patch
> doesn't fix any of those unsafe things.
>
> If it doesn't explain why we need this patch or how this patch works,
> I don't think we need it in the commit log.
>
> Maybe this is an explanation for why you didn't set
> .suppress_auto_claim_dma_owner for shpc_driver?
You are right. This doesn't explain why this is needed and how it works.
It only explains why we don't do the same thing to other pci port
drivers. I will move this out of the commit message. Perhaps put it
in the cover letter or some patches for vifo.
>
> Minor typos above:
> s/in order to avoiding default/before avoiding default/
> s/relies on the PCI MMIO access/relies on PCI MMIO access/
> s/For example, The/For example, the/
> s/is a sure indicate the/is a sure indication the/
Thank you! I will correct these.
>
>> Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
>> Suggested-by: Kevin Tian <kevin.tian@intel.com>
>> Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
>> ---
>> drivers/pci/pcie/portdrv_pci.c | 5 ++++-
>> 1 file changed, 4 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/pci/pcie/portdrv_pci.c b/drivers/pci/pcie/portdrv_pci.c
>> index 35eca6277a96..c48a8734f9c4 100644
>> --- a/drivers/pci/pcie/portdrv_pci.c
>> +++ b/drivers/pci/pcie/portdrv_pci.c
>> @@ -202,7 +202,10 @@ static struct pci_driver pcie_portdriver = {
>>
>> .err_handler = &pcie_portdrv_err_handler,
>>
>> - .driver.pm = PCIE_PORTDRV_PM_OPS,
>> + .driver = {
>> + .pm = PCIE_PORTDRV_PM_OPS,
>> + .suppress_auto_claim_dma_owner = true,
>> + },
>> };
>>
>> static int __init dmi_pcie_pme_disable_msi(const struct dmi_system_id *d)
>> --
>> 2.25.1
>>
Best regards,
baolu
next prev parent reply other threads:[~2021-12-30 5:50 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-17 6:36 [PATCH v4 00/13] Fix BUG_ON in vfio_iommu_group_notifier() Lu Baolu
2021-12-17 6:36 ` [PATCH v4 01/13] iommu: Add device dma ownership set/release interfaces Lu Baolu
2021-12-17 6:36 ` [PATCH v4 02/13] driver core: Set DMA ownership during driver bind/unbind Lu Baolu
2021-12-22 12:47 ` Greg Kroah-Hartman
2021-12-22 17:52 ` Jason Gunthorpe
2021-12-23 2:08 ` Lu Baolu
2021-12-23 3:02 ` Lu Baolu
2021-12-23 7:13 ` Greg Kroah-Hartman
2021-12-23 7:23 ` Lu Baolu
2021-12-31 0:36 ` Jason Gunthorpe
2021-12-17 6:36 ` [PATCH v4 03/13] PCI: pci_stub: Suppress kernel DMA ownership auto-claiming Lu Baolu
2021-12-29 20:42 ` Bjorn Helgaas
2021-12-30 5:34 ` Lu Baolu
2021-12-30 22:24 ` Bjorn Helgaas
2021-12-31 0:40 ` Jason Gunthorpe
2021-12-31 1:10 ` Lu Baolu
2021-12-31 1:58 ` Lu Baolu
2022-01-03 19:53 ` Jason Gunthorpe
2022-01-04 1:54 ` Lu Baolu
2021-12-31 1:06 ` Lu Baolu
2021-12-17 6:36 ` [PATCH v4 04/13] PCI: portdrv: " Lu Baolu
2021-12-29 21:16 ` Bjorn Helgaas
2021-12-30 5:49 ` Lu Baolu [this message]
2021-12-17 6:37 ` [PATCH v4 05/13] iommu: Add security context management for assigned devices Lu Baolu
2021-12-17 6:37 ` [PATCH v4 06/13] iommu: Expose group variants of dma ownership interfaces Lu Baolu
2021-12-17 6:37 ` [PATCH v4 07/13] iommu: Add iommu_at[de]tach_device_shared() for multi-device groups Lu Baolu
2021-12-21 16:50 ` Robin Murphy
2021-12-21 18:46 ` Jason Gunthorpe
2021-12-22 4:22 ` Lu Baolu
2021-12-22 4:25 ` Lu Baolu
2021-12-22 20:26 ` Robin Murphy
2021-12-23 0:57 ` Jason Gunthorpe
2021-12-23 5:53 ` Lu Baolu
2021-12-23 14:03 ` Jason Gunthorpe
2021-12-24 1:30 ` Lu Baolu
2021-12-24 2:50 ` Jason Gunthorpe
2021-12-24 6:44 ` Lu Baolu
2022-01-04 1:53 ` Lu Baolu
2021-12-24 3:19 ` Lu Baolu
2021-12-24 14:24 ` Jason Gunthorpe
2021-12-17 6:37 ` [PATCH v4 08/13] vfio: Set DMA USER ownership for VFIO devices Lu Baolu
2021-12-17 6:37 ` [PATCH v4 09/13] vfio: Remove use of vfio_group_viable() Lu Baolu
2021-12-17 6:37 ` [PATCH v4 10/13] vfio: Delete the unbound_list Lu Baolu
2021-12-17 6:37 ` [PATCH v4 11/13] vfio: Remove iommu group notifier Lu Baolu
2021-12-17 6:37 ` [PATCH v4 12/13] iommu: Remove iommu group changes notifier Lu Baolu
2021-12-17 6:37 ` [PATCH v4 13/13] drm/tegra: Use the iommu dma_owner mechanism Lu Baolu
2022-01-04 5:23 ` [PATCH v4 00/13] Fix BUG_ON in vfio_iommu_group_notifier() Lu Baolu
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