At least the boot process gets all the information it needs (including the
physical addresses associated with untyped memory frames) and also gets the
master I/O capability.
On Sun, Jan 3, 2016 at 3:49 PM, Gerwin Klein <Gerwin.Klein(a)nicta.com.au>
On 26 Dec 2015, at 21:24, Corey Richardson
On Fri, Dec 25, 2015 at 11:19:55PM -0800, Raymond Jennings wrote:
> Speaking of which, how exactly does seL4 enforce no dma on systems
I've been unable to determine this myself. Consider the example of an ATA
controller: it seems you could put any arbitrary address in the PRDT and
it spray disk contents into physical memory. In
this case, all one needs
IOPort for that device's range on the IO bus
and potentially for its
PCI configuration space (to enable bus
The manual seems to be self-contradictory here. In the section about the
BootInfo it indicates that the physical addresses are given to initiate
when no IOMMU is present, but the IOSpace section
states that to use DMA
IOMMU must be used.
I can't really find any way that this is enforced or could be enforced
kernel. In userland it can be done quite easily
by just not giving out
seL4 does not enforce absence of DMA. In general it’s not possible to do
that, that’s why it’s an assumption to the proof that you need to validate
for your system.
Without an IOMMU, you will need to trust the drivers and the hardware of
DMA-capable devices to either not use DMA or to use it safely only.
You can lock down systems to not provide any access at all to DMA-devices,
which sometimes is enough for simple separation-style systems. There are
more trade-off points in the design space, but the trust story does become
massively simpler and better when you have IOMMU support.
With an IOMMU, seL4 is in control and you’re fine.
The information in this e-mail may be confidential and subject to legal
professional privilege and/or copyright. National ICT Australia Limited
accepts no liability for any damage caused by this email or its attachments.