Re: [RFT][PATCH v1 5/6] vfio/ccw: Add kmap_local_page() for memcpy

Christoph Hellwig
2022-06-20T06:32:18Z

On Sun, Jun 19, 2022 at 11:57:26PM -0300, Jason Gunthorpe wrote:
> The remark about io memory is because on s390 memcpy() will crash even
> on ioremapped memory, you have to use the memcpy_to/fromio() which
> uses the special s390 io access instructions.

Yes. The same is true for various other architectures, inluding arm64
under the right circumstances.

> This helps because we now block io memory from ever getting into these
> call paths. I'm pretty sure this is a serious security bug, but would
> let the IBM folks remark as I don't know it all that well..

Prevent as in crash when trying to convert it to a page?

> As for the kmap, I thought it was standard practice even if it is a
> non-highmem? Aren't people trying to use this for other security
> stuff these days?

Ira has been lookin into the protection keys, although they don't
apply to s390. Either way I don't object to using kmap, but the
commit log doesn't make much sense to me.