linux-kernel - Re: [RFC PATCH v2 00/58] KVM: Arm SMMUv3 driver for pKVM

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: <20250122191616.GW674319@ziepe.ca>
Date: Wed, 22 Jan 2025 15:16:16 -0400
From: Jason Gunthorpe <jgg@...pe.ca>
To: Mostafa Saleh <smostafa@...gle.com>
Cc: "Tian, Kevin" <kevin.tian@...el.com>,
	"iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
	"kvmarm@...ts.linux.dev" <kvmarm@...ts.linux.dev>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>,
	"catalin.marinas@....com" <catalin.marinas@....com>,
	"will@...nel.org" <will@...nel.org>,
	"maz@...nel.org" <maz@...nel.org>,
	"oliver.upton@...ux.dev" <oliver.upton@...ux.dev>,
	"joey.gouly@....com" <joey.gouly@....com>,
	"suzuki.poulose@....com" <suzuki.poulose@....com>,
	"yuzenghui@...wei.com" <yuzenghui@...wei.com>,
	"robdclark@...il.com" <robdclark@...il.com>,
	"joro@...tes.org" <joro@...tes.org>,
	"robin.murphy@....com" <robin.murphy@....com>,
	"jean-philippe@...aro.org" <jean-philippe@...aro.org>,
	"nicolinc@...dia.com" <nicolinc@...dia.com>,
	"vdonnefort@...gle.com" <vdonnefort@...gle.com>,
	"qperret@...gle.com" <qperret@...gle.com>,
	"tabba@...gle.com" <tabba@...gle.com>,
	"danielmentz@...gle.com" <danielmentz@...gle.com>,
	"tzukui@...gle.com" <tzukui@...gle.com>
Subject: Re: [RFC PATCH v2 00/58] KVM: Arm SMMUv3 driver for pKVM

On Wed, Jan 22, 2025 at 05:17:50PM +0000, Mostafa Saleh wrote:
> On Wed, Jan 22, 2025 at 12:20:55PM -0400, Jason Gunthorpe wrote:
> > On Wed, Jan 22, 2025 at 11:04:24AM +0000, Mostafa Saleh wrote:
> > > AFAIK, the most common use cases would be:
> > > - Devices using DMA API because it requires a lot of memory to be
> > >   contiguous in IOVA, which is hard to do with identity
> > 
> > This is not a feature of the DMA API any driver should rely on .. Are
> > you aware of one that does?
> > 
> 
> I’d guess one example is media drivers, they usually need large contiguous
> buffers, and would use for ex dma_alloc_coherent(), if the IOMMU is disabled or
> bypassed, that means that the kernel has to find such contiguous size in the
> physical address which can be impossible on devices with small memory as
> mobile devices. Similarly.

I see, that make sense

> It’s not just about completely external devices, it’s a defence in depth
> measure, where for example, network devices can be poked externally an
> there have cases in the past where exploits were found[1], so some vendors
> might have a policy to isolate such devices. Which I believe is a valid.

The performance cost of doing isolation like that with networking is
probably prohibitive with paravirt..

Jason