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

Jason Gunthorpe
2021-05-13T19:20:19Z

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