linux-kernel - Re: [PATCH v4 03/13] PCI: pci_stub: Suppress kernel DMA ownership auto-claiming

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20211230222414.GA1805873@bhelgaas>
Date:   Thu, 30 Dec 2021 16:24:14 -0600
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Lu Baolu <baolu.lu@...ux.intel.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Joerg Roedel <joro@...tes.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Jason Gunthorpe <jgg@...dia.com>,
        Christoph Hellwig <hch@...radead.org>,
        Kevin Tian <kevin.tian@...el.com>,
        Ashok Raj <ashok.raj@...el.com>, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Dan Williams <dan.j.williams@...el.com>, rafael@...nel.org,
        Diana Craciun <diana.craciun@....nxp.com>,
        Cornelia Huck <cohuck@...hat.com>,
        Eric Auger <eric.auger@...hat.com>,
        Liu Yi L <yi.l.liu@...el.com>,
        Jacob jun Pan <jacob.jun.pan@...el.com>,
        Chaitanya Kulkarni <kch@...dia.com>,
        Stuart Yoder <stuyoder@...il.com>,
        Laurentiu Tudor <laurentiu.tudor@....com>,
        Thierry Reding <thierry.reding@...il.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Li Yang <leoyang.li@....com>,
        Dmitry Osipenko <digetx@...il.com>,
        iommu@...ts.linux-foundation.org, linux-pci@...r.kernel.org,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 03/13] PCI: pci_stub: Suppress kernel DMA ownership
 auto-claiming

On Thu, Dec 30, 2021 at 01:34:27PM +0800, Lu Baolu wrote:
> Hi Bjorn,
> 
> On 12/30/21 4:42 AM, Bjorn Helgaas wrote:
> > On Fri, Dec 17, 2021 at 02:36:58PM +0800, Lu Baolu wrote:
> > > The pci_dma_configure() marks the iommu_group as containing only devices
> > > with kernel drivers that manage DMA.
> > 
> > I'm looking at pci_dma_configure(), and I don't see the connection to
> > iommu_groups.
> 
> The 2nd patch "driver core: Set DMA ownership during driver bind/unbind"
> sets all drivers' DMA to be kernel-managed by default except a few ones
> which has a driver flag set. So by default, all iommu groups contains
> only devices with kernel drivers managing DMA.

It looks like that happens in device_dma_configure(), not
pci_dma_configure().

> > > Avoid this default behavior for the
> > > pci_stub because it does not program any DMA itself.  This allows the
> > > pci_stub still able to be used by the admin to block driver binding after
> > > applying the DMA ownership to vfio.
> > 
> > > 
> > > Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
> > > ---
> > >   drivers/pci/pci-stub.c | 3 +++
> > >   1 file changed, 3 insertions(+)
> > > 
> > > diff --git a/drivers/pci/pci-stub.c b/drivers/pci/pci-stub.c
> > > index e408099fea52..6324c68602b4 100644
> > > --- a/drivers/pci/pci-stub.c
> > > +++ b/drivers/pci/pci-stub.c
> > > @@ -36,6 +36,9 @@ static struct pci_driver stub_driver = {
> > >   	.name		= "pci-stub",
> > >   	.id_table	= NULL,	/* only dynamic id's */
> > >   	.probe		= pci_stub_probe,
> > > +	.driver		= {
> > > +		.suppress_auto_claim_dma_owner = true,
> > 
> > The new .suppress_auto_claim_dma_owner controls whether we call
> > iommu_device_set_dma_owner().  I guess you added
> > .suppress_auto_claim_dma_owner because iommu_device_set_dma_owner()
> > must be done *before* we call the driver's .probe() method?
> 
> As explained above, all drivers are set to kernel-managed dma by
> default. For those vfio and vfio-approved drivers,
> suppress_auto_claim_dma_owner is used to tell the driver core that "this
> driver is attached to device for userspace assignment purpose, do not
> claim it for kernel-management dma".
> 
> > Otherwise, we could call some new interface from .probe() instead of
> > adding the flag to struct device_driver.
> 
> Most device drivers are of the kernel-managed DMA type. Only a few vfio
> and vfio-approved drivers need to use this flag. That's the reason why
> we claim kernel-managed DMA by default.

Yes.  But you didn't answer the question of whether this must be done
by a new flag in struct device_driver, or whether it could be done by
having these few VFIO and "VFIO-approved" (whatever that means)
drivers call a new interface.

I was speculating that maybe the DMA ownership claiming must be done
*before* the driver's .probe() method?  If so, that would require a
new flag.  But I don't know whether that's the case.  If DMA
ownership could be claimed by the .probe() method, we wouldn't need
the new flag in struct device_driver.

Bjorn