linux-kernel - [PATCH 1/2] dma-mapping: truncate dma masks to what dma_addr

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Date:   Tue, 21 May 2019 14:47:28 +0200
From:   Christoph Hellwig <hch@....de>
To:     iommu@...ts.linux-foundation.org,
        Russell King <linux@...linux.org.uk>
Cc:     Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH 1/2] dma-mapping: truncate dma masks to what dma_addr_t can hold

The dma masks in struct device are always 64-bits wide.  But for builds
using a 32-bit dma_addr_t we need to ensure we don't store an
unsupportable value.  Before Linux 5.0 this was handled at least by
the ARM dma mapping code by never allowing to set a larger dma_mask,
but these days we allow the driver to just set the largest supported
value and never fall back to a smaller one.  Ensure this always works
by truncating the value.

Fixes: 9eb9e96e97b3 ("Documentation/DMA-API-HOWTO: update dma_mask sections")
Signed-off-by: Christoph Hellwig <hch@....de>
---
 kernel/dma/mapping.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/kernel/dma/mapping.c b/kernel/dma/mapping.c
index f7afdadb6770..1f628e7ac709 100644
--- a/kernel/dma/mapping.c
+++ b/kernel/dma/mapping.c
@@ -317,6 +317,12 @@ void arch_dma_set_mask(struct device *dev, u64 mask);
 
 int dma_set_mask(struct device *dev, u64 mask)
 {
+	/*
+	 * Truncate the mask to the actually supported dma_addr_t width to
+	 * avoid generating unsupportable addresses.
+	 */
+	mask = (dma_addr_t)mask;
+
 	if (!dev->dma_mask || !dma_supported(dev, mask))
 		return -EIO;
 
@@ -330,6 +336,12 @@ EXPORT_SYMBOL(dma_set_mask);
 #ifndef CONFIG_ARCH_HAS_DMA_SET_COHERENT_MASK
 int dma_set_coherent_mask(struct device *dev, u64 mask)
 {
+	/*
+	 * Truncate the mask to the actually supported dma_addr_t width to
+	 * avoid generating unsupportable addresses.
+	 */
+	mask = (dma_addr_t)mask;
+
 	if (!dma_supported(dev, mask))
 		return -EIO;
 
-- 
2.20.1