Re: [PATCH] [EFI,PCI] Allow disabling PCI busmastering on bridges during boot

[Matthew Garrett]

On Mon, Dec 2, 2019 at 4:40 PM Matthew Garrett
<matthewgarrett@xxxxxxxxxx> wrote:
>
> Add an option to disable the busmaster bit in the control register on
> all PCI bridges before calling ExitBootServices() and passing control to
> the runtime kernel. System firmware may configure the IOMMU to prevent
> malicious PCI devices from being able to attack the OS via DMA. However,
> since firmware can't guarantee that the OS is IOMMU-aware, it will tear
> down IOMMU configuration when ExitBootServices() is called. This leaves
> a window between where a hostile device could still cause damage before
> Linux configures the IOMMU again.

I don't know enough about ARM to know if this makes sense there as well. Anyone?