linux-kernel - RE: [PATCH v8 5/9] hisi_acc_vfio_pci: Restrict access to VF dev BAR2 migration region

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Date:   Tue, 8 Mar 2022 08:33:16 +0000
From:   Shameerali Kolothum Thodi <shameerali.kolothum.thodi@...wei.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>
CC:     "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "jgg@...dia.com" <jgg@...dia.com>,
        "cohuck@...hat.com" <cohuck@...hat.com>,
        "mgurtovoy@...dia.com" <mgurtovoy@...dia.com>,
        "yishaih@...dia.com" <yishaih@...dia.com>,
        Linuxarm <linuxarm@...wei.com>,
        liulongfang <liulongfang@...wei.com>,
        "Zengtao (B)" <prime.zeng@...ilicon.com>,
        "Jonathan Cameron" <jonathan.cameron@...wei.com>,
        "Wangzhou (B)" <wangzhou1@...ilicon.com>
Subject: RE: [PATCH v8 5/9] hisi_acc_vfio_pci: Restrict access to VF dev BAR2
 migration region

Hi Kevin,

> -----Original Message-----
> From: Tian, Kevin [mailto:kevin.tian@...el.com]
> Sent: 08 March 2022 06:23
> To: Shameerali Kolothum Thodi <shameerali.kolothum.thodi@...wei.com>;
> kvm@...r.kernel.org; linux-kernel@...r.kernel.org;
> linux-crypto@...r.kernel.org
> Cc: linux-pci@...r.kernel.org; alex.williamson@...hat.com; jgg@...dia.com;
> cohuck@...hat.com; mgurtovoy@...dia.com; yishaih@...dia.com; Linuxarm
> <linuxarm@...wei.com>; liulongfang <liulongfang@...wei.com>; Zengtao (B)
> <prime.zeng@...ilicon.com>; Jonathan Cameron
> <jonathan.cameron@...wei.com>; Wangzhou (B) <wangzhou1@...ilicon.com>
> Subject: RE: [PATCH v8 5/9] hisi_acc_vfio_pci: Restrict access to VF dev BAR2
> migration region
> 
> Hi, Shameer,
> 
> > From: Shameer Kolothum <shameerali.kolothum.thodi@...wei.com>
> > Sent: Friday, March 4, 2022 7:01 AM
> >
> > HiSilicon ACC VF device BAR2 region consists of both functional
> > register space and migration control register space. From a
> > security point of view, it's not advisable to export the migration
> > control region to Guest.
> >
> > Hence, introduce a separate struct vfio_device_ops for migration
> > support which will override the ioctl/read/write/mmap methods to
> > hide the migration region and limit the access only to the
> > functional register space.
> >
> > This will be used in subsequent patches when we add migration
> > support to the driver.
> 
> As a security concern the migration control region should be always
> disabled regardless of whether migration support is added to the
> driver for such device... It sounds like we should first fix this security
> hole for acc device assignment and then add the migration support
> atop (at least organize the series in this way).

By exposing the migration BAR region, there is a possibility that a malicious
Guest can prevent migration from happening by manipulating the migration
BAR region. I don't think there are any other security concerns now especially
since we only support the STOP_COPY state.  And the approach has been that
we only restrict this if migration support is enabled. I think I can change the
above "security concern" description to "malicious Guest can prevent migration"
to make it more clear.

Hope this is fine.

Thanks,
Shameer