[PATCH v2] ARM/dma-mapping: use kvcalloc for fallback memory allocation need

[Deepak R Varma <drv@mailo.com>]

Current conditional determination of whether to use kzalloc or vzalloc
has known issues such as "indefinite retry" when less than PAGE_SIZE
memory is needed, but is unavailable. This LWN article [1] describes
these issues in greater detail. Use helper function kvcalloc() instead
which is more efficient in terms of performance and security.

 	[1] https://lwn.net/Articles/711653/

This patch proposal is based on following Coccinelle warning using the
kvmalloc.cocci semantic patch.
	arch/arm/mm/dma-mapping.c:858:28-29: WARNING opportunity for kvmalloc

The semantic patch suggests using kvzalloc() helper function, however,
this patch proposes to use kvcalloc instead. kvcalloc() helper function
uses 2-factor argument form which is better from a security perspective
as described in the following KSPP project commit.

	Commit 4e3fd7217105 ("wireguard: ratelimiter: use kvcalloc() instead of kvzalloc()")

Signed-off-by: Deepak R Varma <drv@mailo.com>
---

Changes in v2:
   1. Update patch subject to use kvcalloc
   2. Use kvcalloc instead of kvzalloc helper function. Revise the patch
      proposal and the patch description accordingly.


 arch/arm/mm/dma-mapping.c | 6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
index c135f6e37a00..35092ecd30e1 100644
--- a/arch/arm/mm/dma-mapping.c
+++ b/arch/arm/mm/dma-mapping.c
@@ -851,14 +851,10 @@ static struct page **__iommu_alloc_buffer(struct device *dev, size_t size,
 {
 	struct page **pages;
 	int count = size >> PAGE_SHIFT;
-	int array_size = count * sizeof(struct page *);
 	int i = 0;
 	int order_idx = 0;

-	if (array_size <= PAGE_SIZE)
-		pages = kzalloc(array_size, GFP_KERNEL);
-	else
-		pages = vzalloc(array_size);
+	pages = kvcalloc(count, sizeof(struct page *), GFP_KERNEL);
 	if (!pages)
 		return NULL;

--
2.34.1




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