Messages in this thread | | | From | Lu Baolu <> | Subject | [PATCH v3 00/10] iommu: Bounce page for untrusted devices | Date | Sun, 21 Apr 2019 09:17:09 +0800 |
| |
The Thunderbolt vulnerabilities are public and have a nice name as Thunderclap [1] [3] nowadays. This patch series aims to mitigate those concerns.
An external PCI device is a PCI peripheral device connected to the system through an external bus, such as Thunderbolt. What makes it different is that it can't be trusted to the same degree as the devices build into the system. Generally, a trusted PCIe device will DMA into the designated buffers and not overrun or otherwise write outside the specified bounds. But it's different for an external device.
The minimum IOMMU mapping granularity is one page (4k), so for DMA transfers smaller than that a malicious PCIe device can access the whole page of memory even if it does not belong to the driver in question. This opens a possibility for DMA attack. For more information about DMA attacks imposed by an untrusted PCI/PCIe device, please refer to [2].
This implements bounce buffer for the untrusted external devices. The transfers should be limited in isolated pages so the IOMMU window does not cover memory outside of what the driver expects. Full pages within a buffer could be directly mapped in IOMMU page table, but for partial pages we use bounce page instead.
The implementation of bounce buffers for untrusted devices will cause a little performance overhead, but we didn't see any user experience problems. The users could use the kernel parameter defined in the IOMMU driver to remove the performance overhead if they trust their devices enough.
The first part of this patch series (PATCH1/10 ~ 4/10) extends the swiotlb APIs to support bounce buffer in page manner. The second part (PATCH 5/10) introduce the APIs for bounce page:
* iommu_bounce_map(dev, addr, paddr, size, dir, attrs) - Map a buffer start at DMA address @addr in bounce page manner. For buffer parts that doesn't cross a whole minimal IOMMU page, the bounce page policy is applied. A bounce page mapped by swiotlb will be used as the DMA target in the IOMMU page table. Otherwise, the physical address @paddr is mapped instead.
* iommu_bounce_unmap(dev, addr, size, dir, attrs) - Unmap the buffer mapped with iommu_bounce_map(). The bounce page will be torn down after the bounced data get synced.
* iommu_bounce_sync_single(dev, addr, size, dir, target) - Synce the bounced data in case the bounce mapped buffer is reused.
The third part of this patch series (PATCH 6/10 ~ 10/10) uses the bounce page APIs to map/unmap/sync DMA buffers for those untrusted devices in Intel IOMMU driver.
The third part of this patch series depends on a patch set posted here [4] for discussion. It delegates Intel IOMMU DMA domains to the iommu generic layer.
The bounce page idea: Based-on-idea-by: Mika Westerberg <mika.westerberg@intel.com> Based-on-idea-by: Ashok Raj <ashok.raj@intel.com> Based-on-idea-by: Alan Cox <alan.cox@intel.com> Based-on-idea-by: Kevin Tian <kevin.tian@intel.com>
The patch series has been tested by: Tested-by: Xu Pengfei <pengfei.xu@intel.com> Tested-by: Mika Westerberg <mika.westerberg@intel.com>
Reference: [1] https://thunderclap.io/ [2] https://thunderclap.io/thunderclap-paper-ndss2019.pdf [3] https://christian.kellner.me/2019/02/27/thunderclap-and-linux/ [4] https://lkml.org/lkml/2019/3/4/644
Best regards, Lu Baolu
Change log: v2->v3: - The previous v2 was posed here: https://lkml.org/lkml/2019/3/27/157 - Reuse the existing swiotlb APIs for bounce buffer by extending it to support bounce page. - Move the bouce page APIs into iommu generic layer. - This patch series is based on 5.1-rc1.
v1->v2: - The previous v1 was posted here: https://lkml.org/lkml/2019/3/12/66 - Refactor the code to remove struct bounce_param; - During the v1 review cycle, we discussed the possibility of reusing swiotlb code to avoid code dumplication, but we found the swiotlb implementations are not ready for the use of bounce page pool. https://lkml.org/lkml/2019/3/19/259 - This patch series has been rebased to v5.1-rc2.
Lu Baolu (10): iommu: Add helper to get minimal page size of domain swiotlb: Factor out slot allocation and free swiotlb: Limit tlb address range inside slot pool swiotlb: Extend swiotlb to support page bounce iommu: Add bounce page APIs iommu/vt-d: Add trace events for domain map/unmap iommu/vt-d: Keep swiotlb on if bounce page is necessary iommu/vt-d: Check whether device requires bounce buffer iommu/vt-d: Add dma sync ops for untrusted devices iommu/vt-d: Use bounce buffer for untrusted devices
.../admin-guide/kernel-parameters.txt | 5 + drivers/iommu/Kconfig | 15 + drivers/iommu/Makefile | 1 + drivers/iommu/intel-iommu.c | 276 ++++++++++++++---- drivers/iommu/intel-trace.c | 14 + drivers/iommu/iommu.c | 275 +++++++++++++++++ include/linux/dma-mapping.h | 6 + include/linux/iommu.h | 50 ++++ include/trace/events/intel_iommu.h | 132 +++++++++ kernel/dma/swiotlb.c | 117 ++++++-- 10 files changed, 808 insertions(+), 83 deletions(-) create mode 100644 drivers/iommu/intel-trace.c create mode 100644 include/trace/events/intel_iommu.h
-- 2.17.1
| |