[v2,1/2] dma-direct: check for overflows on 32 bit DMA addresses
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Message ID 20191018110044.22062-2-nsaenzjulienne@suse.de
State Superseded
Headers show
Series
  • x86: Get rid of custom DMA functions
Related show

Commit Message

Nicolas Saenz Julienne Oct. 18, 2019, 11 a.m. UTC
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@suse.de>
---
 include/linux/dma-direct.h | 8 ++++++++
 1 file changed, 8 insertions(+)

Comments

Christoph Hellwig Oct. 30, 2019, 9:41 p.m. UTC | #1
On Fri, Oct 18, 2019 at 01:00:43PM +0200, Nicolas Saenz Julienne wrote:
> +#ifndef CONFIG_ARCH_DMA_ADDR_T_64BIT
> +	/* Check if DMA address overflowed */
> +	if (min(addr, addr + size - 1) <
> +		__phys_to_dma(dev, (phys_addr_t)(min_low_pfn << PAGE_SHIFT)))
> +		return false;
> +#endif

Would be nice to use IS_ENABLED and PFN_PHYS here, and I also think we
need to use phys_to_dma to take care of the encryption bit.  If you then
also introduce an end variable we can make the whole thing actually look
nice:

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;

	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);
}

Otherwise this looks sensible to me.
Nicolas Saenz Julienne Oct. 31, 2019, 10:44 a.m. UTC | #2
On Wed, 2019-10-30 at 14:41 -0700, Christoph Hellwig wrote:
> On Fri, Oct 18, 2019 at 01:00:43PM +0200, Nicolas Saenz Julienne wrote:
> > +#ifndef CONFIG_ARCH_DMA_ADDR_T_64BIT
> > +	/* Check if DMA address overflowed */
> > +	if (min(addr, addr + size - 1) <
> > +		__phys_to_dma(dev, (phys_addr_t)(min_low_pfn << PAGE_SHIFT)))
> > +		return false;
> > +#endif
> 
> Would be nice to use IS_ENABLED and PFN_PHYS here, and I also think we
> need to use phys_to_dma to take care of the encryption bit.  If you then
> also introduce an end variable we can make the whole thing actually look
> nice:
> 
> 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;
> 
> 	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);
> }
> 
> Otherwise this looks sensible to me.

Thanks, noted.

Patch
diff mbox series

diff --git a/include/linux/dma-direct.h b/include/linux/dma-direct.h
index adf993a3bd58..af4bb9c81ccc 100644
--- a/include/linux/dma-direct.h
+++ b/include/linux/dma-direct.h
@@ -3,6 +3,7 @@ 
 #define _LINUX_DMA_DIRECT_H 1
 
 #include <linux/dma-mapping.h>
+#include <linux/memblock.h> /* for min_low_pfn */
 #include <linux/mem_encrypt.h>
 
 #ifdef CONFIG_ARCH_HAS_PHYS_TO_DMA
@@ -27,6 +28,13 @@  static inline bool dma_capable(struct device *dev, dma_addr_t addr, size_t size)
 	if (!dev->dma_mask)
 		return false;
 
+#ifndef CONFIG_ARCH_DMA_ADDR_T_64BIT
+	/* Check if DMA address overflowed */
+	if (min(addr, addr + size - 1) <
+		__phys_to_dma(dev, (phys_addr_t)(min_low_pfn << PAGE_SHIFT)))
+		return false;
+#endif
+
 	return addr + size - 1 <=
 		min_not_zero(*dev->dma_mask, dev->bus_dma_mask);
 }