Re: [PATCH v8 00/11] Fix BUG_ON in vfio_iommu_group_notifier()

[Eric Auger]

Hi Lu,

On 3/8/22 6:44 AM, Lu Baolu wrote:
> Hi folks,
>
> The iommu group is the minimal isolation boundary for DMA. Devices in
> a group can access each other's MMIO registers via peer to peer DMA
> and also need share the same I/O address space.
>
> Once the I/O address space is assigned to user control it is no longer
> available to the dma_map* API, which effectively makes the DMA API
> non-working.
>
> Second, userspace can use DMA initiated by a device that it controls
> to access the MMIO spaces of other devices in the group. This allows
> userspace to indirectly attack any kernel owned device and it's driver.
>
> Therefore groups must either be entirely under kernel control or
> userspace control, never a mixture. Unfortunately some systems have
> problems with the granularity of groups and there are a couple of
> important exceptions:
>
>  - pci_stub allows the admin to block driver binding on a device and
>    make it permanently shared with userspace. Since PCI stub does not
>    do DMA it is safe, however the admin must understand that using
>    pci_stub allows userspace to attack whatever device it was bound
>    it.
>
>  - PCI bridges are sometimes included in groups. Typically PCI bridges
>    do not use DMA, and generally do not have MMIO regions.
>
> Generally any device that does not have any MMIO registers is a
> possible candidate for an exception.
>
> Currently vfio adopts a workaround to detect violations of the above
> restrictions by monitoring the driver core BOUND event, and hardwiring
> the above exceptions. Since there is no way for vfio to reject driver
> binding at this point, BUG_ON() is triggered if a violation is
> captured (kernel driver BOUND event on a group which already has some
> devices assigned to userspace). Aside from the bad user experience
> this opens a way for root userspace to crash the kernel, even in high
> integrity configurations, by manipulating the module binding and
> triggering the BUG_ON.
>
> This series solves this problem by making the user/kernel ownership a
> core concept at the IOMMU layer. The driver core enforces kernel
> ownership while drivers are bound and violations now result in a error
> codes during probe, not BUG_ON failures.
>
> Patch partitions:
>   [PATCH 1-4]: Detect DMA ownership conflicts during driver binding;
>   [PATCH 5-7]: Add security context management for assigned devices;
>   [PATCH 8-11]: Various cleanups.
>
> This is also part one of three initial series for IOMMUFD:
>  * Move IOMMU Group security into the iommu layer
>  - Generic IOMMUFD implementation
>  - VFIO ability to consume IOMMUFD
>
> Change log:
> v1: initial post
>   - https://lore.kernel.org/linux-iommu/20211115020552.2378167-1-baolu.lu@xxxxxxxxxxxxxxx/
>
> v2:
>   - https://lore.kernel.org/linux-iommu/20211128025051.355578-1-baolu.lu@xxxxxxxxxxxxxxx/
>
>   - Move kernel dma ownership auto-claiming from driver core to bus
>     callback. [Greg/Christoph/Robin/Jason]
>     https://lore.kernel.org/linux-iommu/20211115020552.2378167-1-baolu.lu@xxxxxxxxxxxxxxx/T/#m153706912b770682cb12e3c28f57e171aa1f9d0c
>
>   - Code and interface refactoring for iommu_set/release_dma_owner()
>     interfaces. [Jason]
>     https://lore.kernel.org/linux-iommu/20211115020552.2378167-1-baolu.lu@xxxxxxxxxxxxxxx/T/#mea70ed8e4e3665aedf32a5a0a7db095bf680325e
>
>   - [NEW]Add new iommu_attach/detach_device_shared() interfaces for
>     multiple devices group. [Robin/Jason]
>     https://lore.kernel.org/linux-iommu/20211115020552.2378167-1-baolu.lu@xxxxxxxxxxxxxxx/T/#mea70ed8e4e3665aedf32a5a0a7db095bf680325e
>
>   - [NEW]Use iommu_attach/detach_device_shared() in drm/tegra drivers.
>
>   - Refactoring and description refinement.
>
> v3:
>   - https://lore.kernel.org/linux-iommu/20211206015903.88687-1-baolu.lu@xxxxxxxxxxxxxxx/
>
>   - Rename bus_type::dma_unconfigure to bus_type::dma_cleanup. [Greg]
>     https://lore.kernel.org/linux-iommu/c3230ace-c878-39db-1663-2b752ff5384e@xxxxxxxxxxxxxxx/T/#m6711e041e47cb0cbe3964fad0a3466f5ae4b3b9b
>
>   - Avoid _platform_dma_configure for platform_bus_type::dma_configure.
>     [Greg]
>     https://lore.kernel.org/linux-iommu/c3230ace-c878-39db-1663-2b752ff5384e@xxxxxxxxxxxxxxx/T/#m43fc46286611aa56a5c0eeaad99d539e5519f3f6
>
>   - Patch "0012-iommu-Add-iommu_at-de-tach_device_shared-for-mult.patch"
>     and "0018-drm-tegra-Use-the-iommu-dma_owner-mechanism.patch" have
>     been tested by Dmitry Osipenko <digetx@xxxxxxxxx>.
>
> v4:
>   - https://lore.kernel.org/linux-iommu/20211217063708.1740334-1-baolu.lu@xxxxxxxxxxxxxxx/
>   - Remove unnecessary tegra->domain chech in the tegra patch. (Jason)
>   - Remove DMA_OWNER_NONE. (Joerg)
>   - Change refcount to unsigned int. (Christoph)
>   - Move mutex lock into group set_dma_owner functions. (Christoph)
>   - Add kernel doc for iommu_attach/detach_domain_shared(). (Christoph)
>   - Move dma auto-claim into driver core. (Jason/Christoph)
>
> v5:
>   - https://lore.kernel.org/linux-iommu/20220104015644.2294354-1-baolu.lu@xxxxxxxxxxxxxxx/
>   - Move kernel dma ownership auto-claiming from driver core to bus
>     callback. (Greg)
>   - Refactor the iommu interfaces to make them more specific.
>     (Jason/Robin)
>   - Simplify the dma ownership implementation by removing the owner
>     type. (Jason)
>   - Commit message refactoring for PCI drivers. (Bjorn)
>   - Move iommu_attach/detach_device() improvement patches into another
>     series as there are a lot of code refactoring and cleanup staffs
>     in various device drivers.
>
> v6:
>   - https://lore.kernel.org/linux-iommu/20220218005521.172832-1-baolu.lu@xxxxxxxxxxxxxxx/
>   - Refine comments and commit mesages.
>   - Rename iommu_group_set_dma_owner() to iommu_group_claim_dma_owner().
>   - Rename iommu_device_use/unuse_kernel_dma() to
>     iommu_device_use/unuse_default_domain().
>   - Remove unnecessary EXPORT_SYMBOL_GPL.
>   - Change flag name from no_kernel_api_dma to driver_managed_dma.
>   - Merge 4 "Add driver dma ownership management" patches into single
>     one.
>
> v7:
>   - We discussed about adding some fields in driver structure and
>     intercepting it in the bus notifier for driver unbinding. We agreed
>     that the driver structure should not be used out of the driver core.
>   - As iommu_group_claim/release_dma_owner() are only used by the VFIO,
>     there're no use cases for multiple calls for a single group.
>   - Add some commit messages in "vfio: Set DMA ownership for
>     VFIO" to describe the intentional enhancement of unsafe bridge
>     drivers.
>   - Comments refinement.
>
> v8:
>   - Move iommu_use_default_domain() to the end of .dma_configure
>     callback to avoid firmware-data-ordering thing.
>     Link: https://lore.kernel.org/linux-iommu/e2698dbe-18e2-1a82-8a12-fe45bc9be534@xxxxxxx/

Feel free to add my T-b
Tested-by: Eric Auger <eric.auger@xxxxxxxxxx>

Thanks

Eric
>   - Add Acked-by from PCI and VFIO maintainers.
>
> This is based on next branch of linux-iommu tree:
> https://git.kernel.org/pub/scm/linux/kernel/git/joro/iommu.git
> and also available on github:
> https://github.com/LuBaolu/intel-iommu/commits/iommu-dma-ownership-v8
>
> Best regards,
> baolu
>
> Jason Gunthorpe (1):
>   vfio: Delete the unbound_list
>
> Lu Baolu (10):
>   iommu: Add DMA ownership management interfaces
>   driver core: Add dma_cleanup callback in bus_type
>   amba: Stop sharing platform_dma_configure()
>   bus: platform,amba,fsl-mc,PCI: Add device DMA ownership management
>   PCI: pci_stub: Set driver_managed_dma
>   PCI: portdrv: Set driver_managed_dma
>   vfio: Set DMA ownership for VFIO devices
>   vfio: Remove use of vfio_group_viable()
>   vfio: Remove iommu group notifier
>   iommu: Remove iommu group changes notifier
>
>  include/linux/amba/bus.h              |   8 +
>  include/linux/device/bus.h            |   3 +
>  include/linux/fsl/mc.h                |   8 +
>  include/linux/iommu.h                 |  54 +++---
>  include/linux/pci.h                   |   8 +
>  include/linux/platform_device.h       |  10 +-
>  drivers/amba/bus.c                    |  37 +++-
>  drivers/base/dd.c                     |   5 +
>  drivers/base/platform.c               |  21 ++-
>  drivers/bus/fsl-mc/fsl-mc-bus.c       |  24 ++-
>  drivers/iommu/iommu.c                 | 228 ++++++++++++++++--------
>  drivers/pci/pci-driver.c              |  18 ++
>  drivers/pci/pci-stub.c                |   1 +
>  drivers/pci/pcie/portdrv_pci.c        |   2 +
>  drivers/vfio/fsl-mc/vfio_fsl_mc.c     |   1 +
>  drivers/vfio/pci/vfio_pci.c           |   1 +
>  drivers/vfio/platform/vfio_amba.c     |   1 +
>  drivers/vfio/platform/vfio_platform.c |   1 +
>  drivers/vfio/vfio.c                   | 245 ++------------------------
>  19 files changed, 338 insertions(+), 338 deletions(-)
>