[PATCH 1/1] iommu: Don't use lazy flush for untrusted device

[PATCH 1/1] iommu: Don't use lazy flush for untrusted device

[Lu Baolu]

The lazy IOTLB flushing setup leaves a time window, in which the device
can still access some system memory, which has already been unmapped by
the device driver. It's not suitable for untrusted devices. A malicious
device might use this to attack the system by obtaining data that it
shouldn't obtain.

Fixes: c588072bba6b5 ("iommu/vt-d: Convert intel iommu driver to the iommu ops")
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
---
 drivers/iommu/dma-iommu.c | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
index f659395e7959..65234e383d6b 100644
--- a/drivers/iommu/dma-iommu.c
+++ b/drivers/iommu/dma-iommu.c
@@ -311,6 +311,11 @@ static void iommu_dma_flush_iotlb_all(struct iova_domain *iovad)
 	domain->ops->flush_iotlb_all(domain);
 }
 
+static bool dev_is_untrusted(struct device *dev)
+{
+	return dev_is_pci(dev) && to_pci_dev(dev)->untrusted;
+}
+
 /**
  * iommu_dma_init_domain - Initialise a DMA mapping domain
  * @domain: IOMMU domain previously prepared by iommu_get_dma_cookie()
@@ -365,8 +370,9 @@ static int iommu_dma_init_domain(struct iommu_domain *domain, dma_addr_t base,
 
 	init_iova_domain(iovad, 1UL << order, base_pfn);
 
-	if (!cookie->fq_domain && !iommu_domain_get_attr(domain,
-			DOMAIN_ATTR_DMA_USE_FLUSH_QUEUE, &attr) && attr) {
+	if (!cookie->fq_domain && (!dev || !dev_is_untrusted(dev)) &&
+	    !iommu_domain_get_attr(domain, DOMAIN_ATTR_DMA_USE_FLUSH_QUEUE, &attr) &&
+	    attr) {
 		if (init_iova_flush_queue(iovad, iommu_dma_flush_iotlb_all,
 					  iommu_dma_entry_dtor))
 			pr_warn("iova flush queue initialization failed\n");
@@ -508,11 +514,6 @@ static void __iommu_dma_unmap_swiotlb(struct device *dev, dma_addr_t dma_addr,
 				iova_align(iovad, size), dir, attrs);
 }
 
-static bool dev_is_untrusted(struct device *dev)
-{
-	return dev_is_pci(dev) && to_pci_dev(dev)->untrusted;
-}
-
 static dma_addr_t __iommu_dma_map(struct device *dev, phys_addr_t phys,
 		size_t size, int prot, u64 dma_mask)
 {
-- 
2.25.1

Re: [PATCH 1/1] iommu: Don't use lazy flush for untrusted device

[Will Deacon]

On Thu, Feb 25, 2021 at 02:14:54PM +0800, Lu Baolu wrote:
> The lazy IOTLB flushing setup leaves a time window, in which the device
> can still access some system memory, which has already been unmapped by
> the device driver. It's not suitable for untrusted devices. A malicious
> device might use this to attack the system by obtaining data that it
> shouldn't obtain.
> 
> Fixes: c588072bba6b5 ("iommu/vt-d: Convert intel iommu driver to the iommu ops")
> Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
> ---
>  drivers/iommu/dma-iommu.c | 15 ++++++++-------
>  1 file changed, 8 insertions(+), 7 deletions(-)

Acked-by: Will Deacon <will@kernel.org>

Will