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

Claire Chang
2021-05-18T06:44:37Z

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 <tientzu@chromium.org>
---
kernel/dma/direct.c | 38 +++++++++++++++++++++++++++++---------
1 file changed, 29 insertions(+), 9 deletions(-)

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);
--
2.31.1.751.gd2f1c929bd-goog