[v7,13/15] dma-direct: Allocate memory from restricted DMA pool if available

Commit Message

Claire Chang May 18, 2021, 6:42 a.m. UTC

The restricted DMA pool is preferred if available.

The restricted DMA pools provide a basic level of protection against the
DMA overwriting buffer contents at unexpected times. However, to protect
against general data leakage and system memory corruption, the system
needs to provide a way to lock down the memory access, e.g., MPU.

Note that since coherent allocation needs remapping, one must set up
another device coherent pool by shared-dma-pool and use
dma_alloc_from_dev_coherent instead for atomic coherent allocation.

Signed-off-by: Claire Chang <[e-mail]>
---
 kernel/dma/direct.c | 38 +++++++++++++++++++++++++++++---------
 1 file changed, 29 insertions(+), 9 deletions(-)

Comments

Christoph Hellwig May 27, 2021, 1:30 p.m. UTC | #1

> +#ifdef CONFIG_DMA_RESTRICTED_POOL
> +	if (swiotlb_free(dev, page, size))
> +		return;
> +#endif

Please avoid the ifdefs by either stubbing out the function to be a no-op
or by using IS_ENABLED.

> +#ifdef CONFIG_DMA_RESTRICTED_POOL
> +	page = swiotlb_alloc(dev, size);
> +	if (page && !dma_coherent_ok(dev, page_to_phys(page), size)) {
> +		__dma_direct_free_pages(dev, page, size);
> +		page = NULL;
> +	}
> +#endif

Same here, for the stub it would just return NULL.

Patch

diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
index eb4098323bbc..0d521f78c7b9 100644
--- a/kernel/dma/direct.c
+++ b/kernel/dma/direct.c
@@ -78,6 +78,10 @@  static bool dma_coherent_ok(struct device *dev, phys_addr_t phys, size_t size)
 static void __dma_direct_free_pages(struct device *dev, struct page *page,
 				    size_t size)
 {
+#ifdef CONFIG_DMA_RESTRICTED_POOL
+	if (swiotlb_free(dev, page, size))
+		return;
+#endif
 	dma_free_contiguous(dev, page, size);
 }
 
@@ -92,7 +96,17 @@  static struct page *__dma_direct_alloc_pages(struct device *dev, size_t size,
 
 	gfp |= dma_direct_optimal_gfp_mask(dev, dev->coherent_dma_mask,
 					   &phys_limit);
-	page = dma_alloc_contiguous(dev, size, gfp);
+
+#ifdef CONFIG_DMA_RESTRICTED_POOL
+	page = swiotlb_alloc(dev, size);
+	if (page && !dma_coherent_ok(dev, page_to_phys(page), size)) {
+		__dma_direct_free_pages(dev, page, size);
+		page = NULL;
+	}
+#endif
+
+	if (!page)
+		page = dma_alloc_contiguous(dev, size, gfp);
 	if (page && !dma_coherent_ok(dev, page_to_phys(page), size)) {
 		dma_free_contiguous(dev, page, size);
 		page = NULL;
@@ -148,7 +162,7 @@  void *dma_direct_alloc(struct device *dev, size_t size,
 		gfp |= __GFP_NOWARN;
 
 	if ((attrs & DMA_ATTR_NO_KERNEL_MAPPING) &&
-	    !force_dma_unencrypted(dev)) {
+	    !force_dma_unencrypted(dev) && !is_dev_swiotlb_force(dev)) {
 		page = __dma_direct_alloc_pages(dev, size, gfp & ~__GFP_ZERO);
 		if (!page)
 			return NULL;
@@ -161,18 +175,23 @@  void *dma_direct_alloc(struct device *dev, size_t size,
 	}
 
 	if (!IS_ENABLED(CONFIG_ARCH_HAS_DMA_SET_UNCACHED) &&
-	    !IS_ENABLED(CONFIG_DMA_DIRECT_REMAP) &&
-	    !dev_is_dma_coherent(dev))
+	    !IS_ENABLED(CONFIG_DMA_DIRECT_REMAP) && !dev_is_dma_coherent(dev) &&
+	    !is_dev_swiotlb_force(dev))
 		return arch_dma_alloc(dev, size, dma_handle, gfp, attrs);
 
 	/*
 	 * Remapping or decrypting memory may block. If either is required and
 	 * we can't block, allocate the memory from the atomic pools.
+	 * If restricted DMA (i.e., is_dev_swiotlb_force) is required, one must
+	 * set up another device coherent pool by shared-dma-pool and use
+	 * dma_alloc_from_dev_coherent instead.
 	 */
 	if (IS_ENABLED(CONFIG_DMA_COHERENT_POOL) &&
 	    !gfpflags_allow_blocking(gfp) &&
 	    (force_dma_unencrypted(dev) ||
-	     (IS_ENABLED(CONFIG_DMA_DIRECT_REMAP) && !dev_is_dma_coherent(dev))))
+	     (IS_ENABLED(CONFIG_DMA_DIRECT_REMAP) &&
+	      !dev_is_dma_coherent(dev))) &&
+	    !is_dev_swiotlb_force(dev))
 		return dma_direct_alloc_from_pool(dev, size, dma_handle, gfp);
 
 	/* we always manually zero the memory once we are done */
@@ -253,15 +272,15 @@  void dma_direct_free(struct device *dev, size_t size,
 	unsigned int page_order = get_order(size);
 
 	if ((attrs & DMA_ATTR_NO_KERNEL_MAPPING) &&
-	    !force_dma_unencrypted(dev)) {
+	    !force_dma_unencrypted(dev) && !is_dev_swiotlb_force(dev)) {
 		/* cpu_addr is a struct page cookie, not a kernel address */
 		dma_free_contiguous(dev, cpu_addr, size);
 		return;
 	}
 
 	if (!IS_ENABLED(CONFIG_ARCH_HAS_DMA_SET_UNCACHED) &&
-	    !IS_ENABLED(CONFIG_DMA_DIRECT_REMAP) &&
-	    !dev_is_dma_coherent(dev)) {
+	    !IS_ENABLED(CONFIG_DMA_DIRECT_REMAP) && !dev_is_dma_coherent(dev) &&
+	    !is_dev_swiotlb_force(dev)) {
 		arch_dma_free(dev, size, cpu_addr, dma_addr, attrs);
 		return;
 	}
@@ -289,7 +308,8 @@  struct page *dma_direct_alloc_pages(struct device *dev, size_t size,
 	void *ret;
 
 	if (IS_ENABLED(CONFIG_DMA_COHERENT_POOL) &&
-	    force_dma_unencrypted(dev) && !gfpflags_allow_blocking(gfp))
+	    force_dma_unencrypted(dev) && !gfpflags_allow_blocking(gfp) &&
+	    !is_dev_swiotlb_force(dev))
 		return dma_direct_alloc_from_pool(dev, size, dma_handle, gfp);
 
 	page = __dma_direct_alloc_pages(dev, size, gfp);