[PATCH] arm64/dma-mapping: Fix null-pointer check

[PATCH] arm64/dma-mapping: Fix null-pointer check

[Olav Haugan]

The current null-pointer check in __dma_alloc_coherent and
__dma_free_coherent is pretty much useless since we are dereferencing
the pointer before checking for null.
Check for null-pointer before the actual dereferencing of the pointer.

Signed-off-by: Olav Haugan <ohaugan@codeaurora.org>
---
 arch/arm64/mm/dma-mapping.c | 21 +++++++++++----------
 1 file changed, 11 insertions(+), 10 deletions(-)

diff --git a/arch/arm64/mm/dma-mapping.c b/arch/arm64/mm/dma-mapping.c
index 3216e098c058..a4b65773711d 100644
--- a/arch/arm64/mm/dma-mapping.c
+++ b/arch/arm64/mm/dma-mapping.c
@@ -95,11 +95,6 @@ static void *__dma_alloc_coherent(struct device *dev, size_t size,
 				  dma_addr_t *dma_handle, gfp_t flags,
 				  unsigned long attrs)
 {
-	if (dev == NULL) {
-		WARN_ONCE(1, "Use an actual device structure for DMA allocation\n");
-		return NULL;
-	}
-
 	if (IS_ENABLED(CONFIG_ZONE_DMA) &&
 	    dev->coherent_dma_mask <= DMA_BIT_MASK(32))
 		flags |= GFP_DMA;
@@ -128,10 +123,6 @@ static void __dma_free_coherent(struct device *dev, size_t size,
 	bool freed;
 	phys_addr_t paddr = dma_to_phys(dev, dma_handle);
 
-	if (dev == NULL) {
-		WARN_ONCE(1, "Use an actual device structure for DMA allocation\n");
-		return;
-	}
 
 	freed = dma_release_from_contiguous(dev,
 					phys_to_page(paddr),
@@ -149,6 +140,11 @@ static void *__dma_alloc(struct device *dev, size_t size,
 	bool coherent = is_device_dma_coherent(dev);
 	pgprot_t prot = __get_dma_pgprot(attrs, PAGE_KERNEL, false);
 
+	if (!dev) {
+		WARN_ONCE(1, "Use an actual device structure for DMA allocation\n");
+		return NULL;
+	}
+
 	size = PAGE_ALIGN(size);
 
 	if (!coherent && !gfpflags_allow_blocking(flags)) {
@@ -192,8 +188,13 @@ static void __dma_free(struct device *dev, size_t size,
 		       void *vaddr, dma_addr_t dma_handle,
 		       unsigned long attrs)
 {
-	void *swiotlb_addr = phys_to_virt(dma_to_phys(dev, dma_handle));
+	void *swiotlb_addr;
 
+	if (!dev) {
+		WARN_ONCE(1, "Use an actual device structure for DMA free\n");
+		return;
+	}
+	swiotlb_addr = phys_to_virt(dma_to_phys(dev, dma_handle));
 	size = PAGE_ALIGN(size);
 
 	if (!is_device_dma_coherent(dev)) {
-- 
2.13.0

Re: [PATCH] arm64/dma-mapping: Fix null-pointer check

[Russell King - ARM Linux]

On Sat, Jun 10, 2017 at 12:41:10PM -0700, Olav Haugan wrote:
> @@ -149,6 +140,11 @@ static void *__dma_alloc(struct device *dev, size_t size,
>  	bool coherent = is_device_dma_coherent(dev);
                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^

This re-introduces an instance that you say you're getting rid of...

>  	pgprot_t prot = __get_dma_pgprot(attrs, PAGE_KERNEL, false);
>  
> +	if (!dev) {
> +		WARN_ONCE(1, "Use an actual device structure for DMA allocation\n");
> +		return NULL;
> +	}
> +
>  	size = PAGE_ALIGN(size);
>  
>  	if (!coherent && !gfpflags_allow_blocking(flags)) {

-- 
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up
according to speedtest.net.

Re: [PATCH] arm64/dma-mapping: Fix null-pointer check

[Olav Haugan]

On 17-06-10 23:03:54, Russell King - ARM Linux wrote:
> On Sat, Jun 10, 2017 at 12:41:10PM -0700, Olav Haugan wrote:
> > @@ -149,6 +140,11 @@ static void *__dma_alloc(struct device *dev, size_t size,
> >  	bool coherent = is_device_dma_coherent(dev);
>                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> 
> This re-introduces an instance that you say you're getting rid of...
> 

The ARM64 version of is_device_dma_coherent() checks for !dev
already...But anyway I will completely remove the !dev checks in the
alloc/free functions since as Catalin pointed out it is coverted
elsewhere.

-- 
.Olav

The Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
a Linux Foundation Collaborative Project

Re: [PATCH] arm64/dma-mapping: Fix null-pointer check

[Catalin Marinas]

On Sat, Jun 10, 2017 at 12:41:10PM -0700, Olav Haugan wrote:
> @@ -149,6 +140,11 @@ static void *__dma_alloc(struct device *dev, size_t size,
>  	bool coherent = is_device_dma_coherent(dev);
>  	pgprot_t prot = __get_dma_pgprot(attrs, PAGE_KERNEL, false);
>  
> +	if (!dev) {
> +		WARN_ONCE(1, "Use an actual device structure for DMA allocation\n");
> +		return NULL;
> +	}
> +
>  	size = PAGE_ALIGN(size);
>  
>  	if (!coherent && !gfpflags_allow_blocking(flags)) {
> @@ -192,8 +188,13 @@ static void __dma_free(struct device *dev, size_t size,
>  		       void *vaddr, dma_addr_t dma_handle,
>  		       unsigned long attrs)
>  {
> -	void *swiotlb_addr = phys_to_virt(dma_to_phys(dev, dma_handle));
> +	void *swiotlb_addr;
>  
> +	if (!dev) {
> +		WARN_ONCE(1, "Use an actual device structure for DMA free\n");
> +		return;
> +	}
> +	swiotlb_addr = phys_to_virt(dma_to_phys(dev, dma_handle));

I don't think we need the checks anymore. With commit 1dccb598df54
("arm64: simplify dma_get_ops") __generic_dma_ops() returns
dummy_dma_ops when dev == NULL, so the above __dma_alloc/__dma_free
functions would not be called.

-- 
Catalin

Re: [PATCH] arm64/dma-mapping: Fix null-pointer check

[Olav Haugan]

On 17-06-12 13:29:04, Catalin Marinas wrote:
> On Sat, Jun 10, 2017 at 12:41:10PM -0700, Olav Haugan wrote:
> > @@ -149,6 +140,11 @@ static void *__dma_alloc(struct device *dev, size_t size,
> >  	bool coherent = is_device_dma_coherent(dev);
> >  	pgprot_t prot = __get_dma_pgprot(attrs, PAGE_KERNEL, false);
> >  
> > +	if (!dev) {
> > +		WARN_ONCE(1, "Use an actual device structure for DMA allocation\n");
> > +		return NULL;
> > +	}
> > +
> >  	size = PAGE_ALIGN(size);
> >  
> >  	if (!coherent && !gfpflags_allow_blocking(flags)) {
> > @@ -192,8 +188,13 @@ static void __dma_free(struct device *dev, size_t size,
> >  		       void *vaddr, dma_addr_t dma_handle,
> >  		       unsigned long attrs)
> >  {
> > -	void *swiotlb_addr = phys_to_virt(dma_to_phys(dev, dma_handle));
> > +	void *swiotlb_addr;
> >  
> > +	if (!dev) {
> > +		WARN_ONCE(1, "Use an actual device structure for DMA free\n");
> > +		return;
> > +	}
> > +	swiotlb_addr = phys_to_virt(dma_to_phys(dev, dma_handle));
> 
> I don't think we need the checks anymore. With commit 1dccb598df54
> ("arm64: simplify dma_get_ops") __generic_dma_ops() returns
> dummy_dma_ops when dev == NULL, so the above __dma_alloc/__dma_free
> functions would not be called.

Ah, you are right. I will remove the checks then! Thanks.

-- 
.Olav

The Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
a Linux Foundation Collaborative Project

Re: [PATCH] arm64/dma-mapping: Fix null-pointer check

[Olav Haugan]

On 17-06-12 13:29:04, Catalin Marinas wrote:
> On Sat, Jun 10, 2017 at 12:41:10PM -0700, Olav Haugan wrote:
> > @@ -149,6 +140,11 @@ static void *__dma_alloc(struct device *dev, size_t size,
> >  	bool coherent = is_device_dma_coherent(dev);
> >  	pgprot_t prot = __get_dma_pgprot(attrs, PAGE_KERNEL, false);
> >  
> > +	if (!dev) {
> > +		WARN_ONCE(1, "Use an actual device structure for DMA allocation\n");
> > +		return NULL;
> > +	}
> > +
> >  	size = PAGE_ALIGN(size);
> >  
> >  	if (!coherent && !gfpflags_allow_blocking(flags)) {
> > @@ -192,8 +188,13 @@ static void __dma_free(struct device *dev, size_t size,
> >  		       void *vaddr, dma_addr_t dma_handle,
> >  		       unsigned long attrs)
> >  {
> > -	void *swiotlb_addr = phys_to_virt(dma_to_phys(dev, dma_handle));
> > +	void *swiotlb_addr;
> >  
> > +	if (!dev) {
> > +		WARN_ONCE(1, "Use an actual device structure for DMA free\n");
> > +		return;
> > +	}
> > +	swiotlb_addr = phys_to_virt(dma_to_phys(dev, dma_handle));
> 
> I don't think we need the checks anymore. With commit 1dccb598df54
> ("arm64: simplify dma_get_ops") __generic_dma_ops() returns
> dummy_dma_ops when dev == NULL, so the above __dma_alloc/__dma_free
> functions would not be called.
> 

We don't need the check in is_device_dma_coherent() either then right?

-- 
.Olav

The Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
a Linux Foundation Collaborative Project

Re: [PATCH] arm64/dma-mapping: Fix null-pointer check

[Catalin Marinas]

On Mon, Jun 12, 2017 at 01:50:28PM -0700, Olav Haugan wrote:
> On 17-06-12 13:29:04, Catalin Marinas wrote:
> > On Sat, Jun 10, 2017 at 12:41:10PM -0700, Olav Haugan wrote:
> > > @@ -149,6 +140,11 @@ static void *__dma_alloc(struct device *dev, size_t size,
> > >  	bool coherent = is_device_dma_coherent(dev);
> > >  	pgprot_t prot = __get_dma_pgprot(attrs, PAGE_KERNEL, false);
> > >  
> > > +	if (!dev) {
> > > +		WARN_ONCE(1, "Use an actual device structure for DMA allocation\n");
> > > +		return NULL;
> > > +	}
> > > +
> > >  	size = PAGE_ALIGN(size);
> > >  
> > >  	if (!coherent && !gfpflags_allow_blocking(flags)) {
> > > @@ -192,8 +188,13 @@ static void __dma_free(struct device *dev, size_t size,
> > >  		       void *vaddr, dma_addr_t dma_handle,
> > >  		       unsigned long attrs)
> > >  {
> > > -	void *swiotlb_addr = phys_to_virt(dma_to_phys(dev, dma_handle));
> > > +	void *swiotlb_addr;
> > >  
> > > +	if (!dev) {
> > > +		WARN_ONCE(1, "Use an actual device structure for DMA free\n");
> > > +		return;
> > > +	}
> > > +	swiotlb_addr = phys_to_virt(dma_to_phys(dev, dma_handle));
> > 
> > I don't think we need the checks anymore. With commit 1dccb598df54
> > ("arm64: simplify dma_get_ops") __generic_dma_ops() returns
> > dummy_dma_ops when dev == NULL, so the above __dma_alloc/__dma_free
> > functions would not be called.
> 
> We don't need the check in is_device_dma_coherent() either then right?

Right. The only user of this function outside
arch/arm64/mm/dma-mapping.c is Xen (shared with arm32 under
arch/arm/xen/) but since arm32 doesn't do this NULL check either, we
should be fine.

-- 
Catalin