linux-kernel - RE: [PATCH v3 00/10] Add Intel VT-d nested translation

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Message-ID: <BN9PR11MB5276281676BAC321CB08D1048C58A@BN9PR11MB5276.namprd11.prod.outlook.com>
Date:   Fri, 16 Jun 2023 02:29:34 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Jason Gunthorpe <jgg@...dia.com>
CC:     "Liu, Yi L" <yi.l.liu@...el.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "robin.murphy@....com" <robin.murphy@....com>,
        "baolu.lu@...ux.intel.com" <baolu.lu@...ux.intel.com>,
        "cohuck@...hat.com" <cohuck@...hat.com>,
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        "nicolinc@...dia.com" <nicolinc@...dia.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "mjrosato@...ux.ibm.com" <mjrosato@...ux.ibm.com>,
        "chao.p.peng@...ux.intel.com" <chao.p.peng@...ux.intel.com>,
        "yi.y.sun@...ux.intel.com" <yi.y.sun@...ux.intel.com>,
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        <shameerali.kolothum.thodi@...wei.com>,
        "lulu@...hat.com" <lulu@...hat.com>,
        "suravee.suthikulpanit@....com" <suravee.suthikulpanit@....com>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>,
        "Duan, Zhenzhong" <zhenzhong.duan@...el.com>
Subject: RE: [PATCH v3 00/10] Add Intel VT-d nested translation

> From: Jason Gunthorpe <jgg@...dia.com>
> Sent: Wednesday, June 14, 2023 7:53 PM
> 
> On Wed, Jun 14, 2023 at 08:07:30AM +0000, Tian, Kevin wrote:
> 
> > think of a scenario where the vbios memory is shared by multiple qemu
> > instances then RW allows a malicious VM to modify the shared content
> > then potentially attacking other VMs.
> 
> qemu would have to map the vbios as MAP_PRIVATE WRITE before the
> iommu
> side could map it writable, so this is not a real worry.
> 

Make sense.

but IMHO it's still safer to reduce the permission (RO->NP) than increasing
the permission (RO->RW) when faithfully emulating bare metal behavior
is impossible, especially when there is no real usage counting on it. 😊