[PATCH 5/5] dma-direct: zero memory allocated with DMA_ATTR_NO_KERNEL_MAPPING

[Marek Szyprowski]

dma_direct_alloc_no_mapping() explicitly clears __GFP_ZERO before
allocating the pages, so buffers allocated with
DMA_ATTR_NO_KERNEL_MAPPING are handed out with stale contents of the
previously freed pages. Such buffers are typically passed to devices or
mapped to userspace, which may expose old kernel data.

The mask comes from the regular allocation path, which always zeroes the
buffer manually through its kernel mapping once it is set up. The
DMA_ATTR_NO_KERNEL_MAPPING path returns early with only a page cookie,
so it never reaches that memset(). This has been the case since the
attribute was first supported in the generic remap code in commit
e440e26a0251 ("dma-remap: support DMA_ATTR_NO_KERNEL_MAPPING") and was
carried over during dma-direct refactoring.

All other dma_alloc_* paths always return zeroed memory, so do the same
here and pass __GFP_ZERO to the page allocator instead of masking it out.

Fixes: e440e26a0251 ("dma-remap: support DMA_ATTR_NO_KERNEL_MAPPING")
Fixes: d98849aff879 ("dma-direct: handle DMA_ATTR_NO_KERNEL_MAPPING in common code")
Fixes: cf14be0b41c6 ("dma-direct: fix DMA_ATTR_NO_KERNEL_MAPPING")
Fixes: 849facea92fa ("dma-direct: simplify the DMA_ATTR_NO_KERNEL_MAPPING handling")
Closes: https://sashiko.dev/#/bug/linux-c4421083-e44e-4373-a2c2-45649ea49c0b
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
---
 kernel/dma/direct.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
index 25e9a86835fd..c8a1ae7c618d 100644
--- a/kernel/dma/direct.c
+++ b/kernel/dma/direct.c
@@ -202,7 +202,8 @@ static void *dma_direct_alloc_no_mapping(struct device *dev, size_t size,
 {
 	struct page *page;
 
-	page = __dma_direct_alloc_pages(dev, size, gfp & ~__GFP_ZERO, true);
+	/* always zero the allocated memory */
+	page = __dma_direct_alloc_pages(dev, size, gfp | __GFP_ZERO, true);
 	if (!page)
 		return NULL;
 
-- 
2.43.0