linux-kernel - [PATCH v2 2/8] iommu/dma: Fail unaligned map requests for untrusted devs

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Date:   Sat, 28 Aug 2021 17:36:36 +0200
From:   Sven Peter <sven@...npeter.dev>
To:     iommu@...ts.linux-foundation.org
Cc:     Sven Peter <sven@...npeter.dev>, Joerg Roedel <joro@...tes.org>,
        Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Arnd Bergmann <arnd@...nel.org>,
        Mohamed Mediouni <mohamed.mediouni@...amail.com>,
        Alexander Graf <graf@...zon.com>,
        Hector Martin <marcan@...can.st>,
        Alyssa Rosenzweig <alyssa@...enzweig.io>,
        linux-kernel@...r.kernel.org
Subject: [PATCH v2 2/8] iommu/dma: Fail unaligned map requests for untrusted devs

If swiotlb is enabled we should never try to create any mappings that
would expose more memory than requested to the device.
WARN_ON and refuse those mappings just in case.

Signed-off-by: Sven Peter <sven@...npeter.dev>
---
 drivers/iommu/dma-iommu.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
index e8eae34e9e4f..d6e273ec3de6 100644
--- a/drivers/iommu/dma-iommu.c
+++ b/drivers/iommu/dma-iommu.c
@@ -534,13 +534,20 @@ static dma_addr_t __iommu_dma_map(struct device *dev, phys_addr_t phys,
 	struct iommu_dma_cookie *cookie = domain->iova_cookie;
 	struct iova_domain *iovad = &cookie->iovad;
 	size_t iova_off = iova_offset(iovad, phys);
+	size_t size_aligned = iova_align(iovad, size + iova_off);
 	dma_addr_t iova;
 
 	if (static_branch_unlikely(&iommu_deferred_attach_enabled) &&
 	    iommu_deferred_attach(dev, domain))
 		return DMA_MAPPING_ERROR;
 
-	size = iova_align(iovad, size + iova_off);
+	if (IS_ENABLED(CONFIG_SWIOTLB) && dev_is_untrusted(dev)) {
+		if (WARN_ON(iova_off))
+			return DMA_MAPPING_ERROR;
+		if (WARN_ON(size_aligned != size))
+			return DMA_MAPPING_ERROR;
+	}
+	size = size_aligned;
 
 	iova = iommu_dma_alloc_iova(domain, size, dma_mask, dev);
 	if (!iova)
-- 
2.25.1