[PATCH] ARM: dma-mapping: add check for coherent DMA memory without struct page

[PATCH] ARM: dma-mapping: add check for coherent DMA memory without struct page

[Shuah Khan]

When coherent DMA memory without struct page is shared, importer
fails to find the page and runs into kernel page fault when it
tries to dmabuf_ops_attach/map_sg/map_page the invalid page found
in the sg_table.

Add a new dma_check_dev_coherent() interface to check if memory is
from the device coherent area. There is no way to tell where the
memory returned by dma_alloc_attrs() came from.

arm_dma_get_sgtable() checks for invalid pages, however this check
could pass even for memory obtained the coherent allocator. Add an
additional check to call dma_check_dev_coherent() to confirm that it
is indeed the coherent DMA memory and fail the sgtable creation with
-EINVAL.

Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>
---
 arch/arm/mm/dma-mapping.c   | 11 ++++++++---
 drivers/base/dma-coherent.c | 25 +++++++++++++++++++++++++
 include/linux/dma-mapping.h |  2 ++
 3 files changed, 35 insertions(+), 3 deletions(-)

diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
index 475811f..27c7d9a 100644
--- a/arch/arm/mm/dma-mapping.c
+++ b/arch/arm/mm/dma-mapping.c
@@ -954,9 +954,14 @@ int arm_dma_get_sgtable(struct device *dev, struct sg_table *sgt,
 	struct page *page;
 	int ret;
 
-	/* If the PFN is not valid, we do not have a struct page */
-	if (!pfn_valid(pfn))
-		return -ENXIO;
+	/*
+	 * If the PFN is not valid, we do not have a struct page
+	 * As this check can pass even for memory obtained through
+	 * the coherent allocator, do an additional check to determine
+	 * if this is coherent DMA memory.
+	 */
+	if (!pfn_valid(pfn) && dma_check_dev_coherent(dev, handle, cpu_addr))
+		return -EINVAL;
 
 	page = pfn_to_page(pfn);
 
diff --git a/drivers/base/dma-coherent.c b/drivers/base/dma-coherent.c
index 640a7e6..d08cf44 100644
--- a/drivers/base/dma-coherent.c
+++ b/drivers/base/dma-coherent.c
@@ -209,6 +209,31 @@ int dma_alloc_from_coherent(struct device *dev, ssize_t size,
 EXPORT_SYMBOL(dma_alloc_from_coherent);
 
 /**
+ * dma_check_dev_coherent() - checks if memory is from the device coherent area
+ *
+ * @dev:	device whose coherent area is checked to validate memory
+ * @dma_handle:	dma handle associated with the allocated memory
+ * @vaddr:	the virtual address to the allocated area.
+ *
+ * Returns true if memory does belong to the per-device cohrent area.
+ * false otherwise.
+ */
+bool dma_check_dev_coherent(struct device *dev, dma_addr_t dma_handle,
+				void *vaddr)
+{
+	struct dma_coherent_mem *mem = dev ? dev->dma_mem : NULL;
+
+	if (mem && vaddr >= mem->virt_base &&
+	    vaddr < (mem->virt_base + (mem->size << PAGE_SHIFT)) &&
+	    dma_handle >= mem->device_base &&
+	    dma_handle < (mem->device_base + (mem->size << PAGE_SHIFT)))
+		return true;
+
+	return false;
+}
+EXPORT_SYMBOL(dma_check_dev_coherent);
+
+/**
  * dma_release_from_coherent() - try to free the memory allocated from per-device coherent memory pool
  * @dev:	device from which the memory was allocated
  * @order:	the order of pages allocated
diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
index 0977317..b10e70d 100644
--- a/include/linux/dma-mapping.h
+++ b/include/linux/dma-mapping.h
@@ -160,6 +160,8 @@ static inline int is_device_dma_capable(struct device *dev)
  */
 int dma_alloc_from_coherent(struct device *dev, ssize_t size,
 				       dma_addr_t *dma_handle, void **ret);
+bool dma_check_dev_coherent(struct device *dev, dma_addr_t dma_handle,
+				void *vaddr);
 int dma_release_from_coherent(struct device *dev, int order, void *vaddr);
 
 int dma_mmap_from_coherent(struct device *dev, struct vm_area_struct *vma,
-- 
2.7.4

Re: [PATCH] ARM: dma-mapping: add check for coherent DMA memory without struct page

[Russell King - ARM Linux]

On Thu, Apr 13, 2017 at 03:47:56PM -0600, Shuah Khan wrote:
> When coherent DMA memory without struct page is shared, importer
> fails to find the page and runs into kernel page fault when it
> tries to dmabuf_ops_attach/map_sg/map_page the invalid page found
> in the sg_table.
> 
> Add a new dma_check_dev_coherent() interface to check if memory is
> from the device coherent area. There is no way to tell where the
> memory returned by dma_alloc_attrs() came from.
> 
> arm_dma_get_sgtable() checks for invalid pages, however this check
> could pass even for memory obtained the coherent allocator. Add an
> additional check to call dma_check_dev_coherent() to confirm that it
> is indeed the coherent DMA memory and fail the sgtable creation with
> -EINVAL.

Sorry, this doesn't make much sense to me.

pfn_valid(pfn) must *never* return true if 'pfn' does not have a struct
page associated with it.  If it returns true (so we allow
arm_dma_get_sgtable() to succeed) then we know we have a valid struct
page in the supplied scatterlist.

> Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>
> ---
>  arch/arm/mm/dma-mapping.c   | 11 ++++++++---
>  drivers/base/dma-coherent.c | 25 +++++++++++++++++++++++++
>  include/linux/dma-mapping.h |  2 ++
>  3 files changed, 35 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
> index 475811f..27c7d9a 100644
> --- a/arch/arm/mm/dma-mapping.c
> +++ b/arch/arm/mm/dma-mapping.c
> @@ -954,9 +954,14 @@ int arm_dma_get_sgtable(struct device *dev, struct sg_table *sgt,
>  	struct page *page;
>  	int ret;
>  
> -	/* If the PFN is not valid, we do not have a struct page */
> -	if (!pfn_valid(pfn))
> -		return -ENXIO;
> +	/*
> +	 * If the PFN is not valid, we do not have a struct page
> +	 * As this check can pass even for memory obtained through
> +	 * the coherent allocator, do an additional check to determine
> +	 * if this is coherent DMA memory.
> +	 */
> +	if (!pfn_valid(pfn) && dma_check_dev_coherent(dev, handle, cpu_addr))
> +		return -EINVAL;

Right, so what this says is:

	if we do not haev a valid PFN
	_and_ if the memory is from the coherent section
	_then_ fail

Why the extra check?  Under what circunstances do we end up with memory
where the PFN is valid, but we do not have a valid struct page.  It
seems to me that such a scenario is a bug in pfn_valid() and not
something that should be worked around like this.

-- 
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] ARM: dma-mapping: add check for coherent DMA memory without struct page

[Shuah Khan]

On 04/13/2017 04:10 PM, Russell King - ARM Linux wrote:
> On Thu, Apr 13, 2017 at 03:47:56PM -0600, Shuah Khan wrote:
>> When coherent DMA memory without struct page is shared, importer
>> fails to find the page and runs into kernel page fault when it
>> tries to dmabuf_ops_attach/map_sg/map_page the invalid page found
>> in the sg_table.
>>
>> Add a new dma_check_dev_coherent() interface to check if memory is
>> from the device coherent area. There is no way to tell where the
>> memory returned by dma_alloc_attrs() came from.
>>
>> arm_dma_get_sgtable() checks for invalid pages, however this check
>> could pass even for memory obtained the coherent allocator. Add an
>> additional check to call dma_check_dev_coherent() to confirm that it
>> is indeed the coherent DMA memory and fail the sgtable creation with
>> -EINVAL.
> 
> Sorry, this doesn't make much sense to me.
> 
> pfn_valid(pfn) must *never* return true if 'pfn' does not have a struct
> page associated with it.  If it returns true (so we allow
> arm_dma_get_sgtable() to succeed) then we know we have a valid struct
> page in the supplied scatterlist.
> 
>> Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>
>> ---
>>  arch/arm/mm/dma-mapping.c   | 11 ++++++++---
>>  drivers/base/dma-coherent.c | 25 +++++++++++++++++++++++++
>>  include/linux/dma-mapping.h |  2 ++
>>  3 files changed, 35 insertions(+), 3 deletions(-)
>>
>> diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
>> index 475811f..27c7d9a 100644
>> --- a/arch/arm/mm/dma-mapping.c
>> +++ b/arch/arm/mm/dma-mapping.c
>> @@ -954,9 +954,14 @@ int arm_dma_get_sgtable(struct device *dev, struct sg_table *sgt,
>>  	struct page *page;
>>  	int ret;
>>  
>> -	/* If the PFN is not valid, we do not have a struct page */
>> -	if (!pfn_valid(pfn))
>> -		return -ENXIO;
>> +	/*
>> +	 * If the PFN is not valid, we do not have a struct page
>> +	 * As this check can pass even for memory obtained through
>> +	 * the coherent allocator, do an additional check to determine
>> +	 * if this is coherent DMA memory.
>> +	 */
>> +	if (!pfn_valid(pfn) && dma_check_dev_coherent(dev, handle, cpu_addr))
>> +		return -EINVAL;
> 
> Right, so what this says is:
> 
> 	if we do not haev a valid PFN
> 	_and_ if the memory is from the coherent section
> 	_then_ fail
> 
> Why the extra check?  Under what circunstances do we end up with memory
> where the PFN is valid, but we do not have a valid struct page.  It
> seems to me that such a scenario is a bug in pfn_valid() and not
> something that should be worked around like this.
> 

DMA_ATTR_NO_KERNEL_MAPPING case is the one I am concerned about.
pfn_valid() would fail on this if I am understanding it correctly.
A few drm drivers set this attr and use sg_table for passing buffers.

My reasoning behind adding this check is to not have this fail on
NO_KERNEL_MAPPING cases. So I thought adding a restrictive check for
just the per-device memory would help. However, I don't have a good
understanding of the drm case, hence I could be trying to address a
case that doesn't need to be addressed.

In any case, thanks for your patience and a quick reply.

-- Shuah