[PATCH v4 11/15] pci: Add pci_iomap_shared{,_range}

Andi Kleen
Tue, 24 Aug 2021 17:20:44 -0000

> I see. Hmm. It's a bit of a random thing to do it at the map time
> though. E.g. DMA is all handled transparently behind the DMA API.
> Hardening is much more than just replacing map with map_shared
> and I suspect what you will end up with is basically
> vendors replacing map with map shared to make things work
> for their users and washing their hands.

That concept exists too. There is a separate allow list for the drivers.
So just adding shared to a driver is not enough, until it's also added
to the allowlist

Users can of course chose to disable the allowlist, but they need to
understand the security implications.


>
> I would say an explicit flag in the driver that says "hardened"
> and refusing to init a non hardened one would be better.


We have that too (that's the device filtering)

But the problem is that device filtering just stops the probe functions,
not the initcalls, and lot of legacy drivers do MMIO interactions before
going into probe. In some cases it's unavoidable because of the device
doesn't have a separate enumeration mechanism it needs some kind of
probing to even check for its existence And since we don't want to
change all of them it's far safer to make the ioremap opt-in.


-Andi