[PATCH v4 0/6] Add support for privileged mappings

Mitchel Humpherys
2016-07-25T19:16:28Z

The following patch to the ARM SMMU driver:

commit d346180e70b91b3d5a1ae7e5603e65593d4622bc
Author: Robin Murphy <robin.murphy@arm.com>
Date: Tue Jan 26 18:06:34 2016 +0000

iommu/arm-smmu: Treat all device transactions as unprivileged

started forcing all SMMU transactions to come through as "unprivileged".
The rationale given was that:

(1) There is no way in the IOMMU API to even request privileged mappings.

(2) It's difficult to implement a DMA mapper that correctly models the
ARM VMSAv8 behavior of unprivileged-writeable =>
privileged-execute-never.

This series rectifies (1) by introducing an IOMMU API for privileged
mappings and implements it in io-pgtable-arm.

This series rectifies (2) by introducing a new dma attribute
(DMA_ATTR_PRIVILEGED) for users of the DMA API that need privileged
mappings which are inaccessible to lesser-privileged execution levels, and
implements it in the arm64 IOMMU DMA mapper. The one known user (pl330.c)
is converted over to the new attribute.

Jordan and Jeremy can provide more info on the use case if needed, but the
high level is that it's a security feature to prevent attacks such as [1].

Joerg, the v3 series was previously acked by Will [2]. He also recommended
that we take all of this through your tree since it's touching multiple
subsystems [3]. Can you please take a look? Thanks!

[1] https://github.com/robclark/kilroy
[2] http://article.gmane.org/gmane.linux.kernel.iommu/14617
[3] http://article.gmane.org/gmane.linux.kernel/2272531

Changelog:

v3..v4

- Rebased and reworked on linux next due to the dma attrs rework going
on over there. Patches changed: 3/6, 4/6, and 5/6.

v2..v3

- Incorporated feedback from Robin:
* Various comments and re-wordings.
* Use existing bit definitions for IOMMU_PRIV implementation
in io-pgtable-arm.
* Renamed and redocumented dma_direction_to_prot.
* Don't worry about executability in new DMA attr.

v1..v2

- Added a new DMA attribute to make executable privileged mappings
work, and use that in the pl330 driver (suggested by Will).

Jeremy Gebben (1):
iommu/io-pgtable-arm: add support for the IOMMU_PRIV flag

Mitchel Humpherys (5):
iommu: add IOMMU_PRIV attribute
common: DMA-mapping: add DMA_ATTR_PRIVILEGED attribute
arm64/dma-mapping: Implement DMA_ATTR_PRIVILEGED
dmaengine: pl330: Make sure microcode is privileged
Revert "iommu/arm-smmu: Treat all device transactions as unprivileged"

Documentation/DMA-attributes.txt | 10 ++++++++++
arch/arm64/mm/dma-mapping.c | 6 +++---
drivers/dma/pl330.c | 6 ++++--
drivers/iommu/arm-smmu.c | 5 +----
drivers/iommu/dma-iommu.c | 16 +++++++++++-----
drivers/iommu/io-pgtable-arm.c | 5 ++++-
include/linux/dma-iommu.h | 3 ++-
include/linux/dma-mapping.h | 6 ++++++
include/linux/iommu.h | 1 +
9 files changed, 42 insertions(+), 16 deletions(-)