linux-kernel - [PATCH v3 1/2] dma-direct: check for overflows on 32 bit DMA addresses

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Message-Id: <20191107150646.13485-2-nsaenzjulienne@suse.de>
Date:   Thu,  7 Nov 2019 16:06:44 +0100
From:   Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
To:     rubini@...dd.com, hch@...radead.org, linux-kernel@...r.kernel.org,
        Christoph Hellwig <hch@....de>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>
Cc:     Nicolas Saenz Julienne <nsaenzjulienne@...e.de>,
        iommu@...ts.linux-foundation.org
Subject: [PATCH v3 1/2] dma-direct: check for overflows on 32 bit DMA addresses

As seen on the new Raspberry Pi 4 and sta2x11's DMA implementation it is
possible for a device configured with 32 bit DMA addresses and a partial
DMA mapping located at the end of the address space to overflow. It
happens when a higher physical address, not DMAable, is translated to
it's DMA counterpart.

For example the Raspberry Pi 4, configurable up to 4 GB of memory, has
an interconnect capable of addressing the lower 1 GB of physical memory
with a DMA offset of 0xc0000000. It transpires that, any attempt to
translate physical addresses higher than the first GB will result in an
overflow which dma_capable() can't detect as it only checks for
addresses bigger then the maximum allowed DMA address.

Fix this by verifying in dma_capable() if the DMA address range provided
is at any point lower than the minimum possible DMA address on the bus.

Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@...e.de>

---

Changes since v2:
  - Cleanup code: use IS_ENABLED, a tmp variable for end, and
    use phys_to_dma().

 include/linux/dma-direct.h | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/include/linux/dma-direct.h b/include/linux/dma-direct.h
index adf993a3bd58..6a18a97b76a8 100644
--- a/include/linux/dma-direct.h
+++ b/include/linux/dma-direct.h
@@ -3,8 +3,11 @@
 #define _LINUX_DMA_DIRECT_H 1

 #include <linux/dma-mapping.h>
+#include <linux/memblock.h> /* for min_low_pfn */
 #include <linux/mem_encrypt.h>

+static inline dma_addr_t phys_to_dma(struct device *dev, phys_addr_t paddr);
+
 #ifdef CONFIG_ARCH_HAS_PHYS_TO_DMA
 #include <asm/dma-direct.h>
 #else
@@ -24,11 +27,16 @@ static inline phys_addr_t __dma_to_phys(struct device *dev, dma_addr_t dev_addr)

 static inline bool dma_capable(struct device *dev, dma_addr_t addr, size_t size)
 {
+	dma_addr_t end = addr + size - 1;
+
 	if (!dev->dma_mask)
 		return false;

-	return addr + size - 1 <=
-		min_not_zero(*dev->dma_mask, dev->bus_dma_mask);
+	if (!IS_ENABLED(CONFIG_ARCH_DMA_ADDR_T_64BIT) &&
+	    min(addr, end) < phys_to_dma(dev, PFN_PHYS(min_low_pfn)))
+		return false;
+
+	return end <= min_not_zero(*dev->dma_mask, dev->bus_dma_mask);
 }
 #endif /* !CONFIG_ARCH_HAS_PHYS_TO_DMA */

-- 
2.23.0