linux-kernel - Re: [PATCH v4 1/2] iommu/sva: Tighten SVA bind API with explicit flags

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Date:   Thu, 13 May 2021 16:20:14 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     "Luck, Tony" <tony.luck@...el.com>
Cc:     Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        Christoph Hellwig <hch@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        Joerg Roedel <joro@...tes.org>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        "wangzhou1@...ilicon.com" <wangzhou1@...ilicon.com>,
        "zhangfei.gao@...aro.org" <zhangfei.gao@...aro.org>,
        "vkoul@...nel.org" <vkoul@...nel.org>,
        David Woodhouse <dwmw2@...radead.org>
Subject: Re: [PATCH v4 1/2] iommu/sva: Tighten SVA bind API with explicit
 flags

On Thu, May 13, 2021 at 07:14:54PM +0000, Luck, Tony wrote:
> > If you want this then be explicit about what it is you are making when
> > building the API. Don't try to hide it under some generic idea of
> > "kernel PCI DMA SVA"
> 
> So, a special API call (that Dave can call from IDXD) to set up this
> kernel PASID. With suitable documentation to explain the scope.
> Maybe with a separate CONFIG option so it can be completely
> stubbed out (IDXD does *NOT* "select" this option ... users have
> to explicitly pick it).
> 
> > I could easily see an admin option to "turn this off" entirely as
> > being too dangerous, especially if the users have no interest in IDXD.
> 
> And a kernel command line option to block IDXD from using that
> special API ... for users on generic kernels who want to block
> this use model (but still use IDXD in non-kernel cases). Users
> who don't want IDXD at all can block loading of the driver.

A generic IOMMU API should not be IDXD specific, if you want to allow
some special "integrated to the SOC accelerator PASID" mode then it
should be a global IOMMU API and any security toggles for it should be
global and unrelated to IDXD.

Concurrently it seems necessary to have a solution for secure kernel
PASID use under the DMA API and reserve this special mode for getting
higher performance.

I think you need to come with a proposal, and it is a bit alarming a
noteworthy security hole was added under the guise of "kernel SVA" :(

Jason