[PATCH v4 22/45] dma: kmsan: unpoison DMA mappings

Alexander Potapenko
2022-07-01T14:27:06Z

KMSAN doesn't know about DMA memory writes performed by devices.
We unpoison such memory when it's mapped to avoid false positive
reports.

Signed-off-by: Alexander Potapenko <glider@google.com>
---
v2:
-- move implementation of kmsan_handle_dma() and kmsan_handle_dma_sg() here

v4:
-- swap dma: and kmsan: int the subject

Link: https://linux-review.googlesource.com/id/Ia162dc4c5a92e74d4686c1be32a4dfeffc5c32cd
---
include/linux/kmsan.h | 41 +++++++++++++++++++++++++++++
kernel/dma/mapping.c | 9 ++++---
mm/kmsan/hooks.c | 61 +++++++++++++++++++++++++++++++++++++++++++
3 files changed, 108 insertions(+), 3 deletions(-)

diff --git a/include/linux/kmsan.h b/include/linux/kmsan.h
index 82fd564cc72e7..55fe673ee1e84 100644
--- a/include/linux/kmsan.h
+++ b/include/linux/kmsan.h
@@ -9,6 +9,7 @@
#ifndef _LINUX_KMSAN_H
#define _LINUX_KMSAN_H

+#include <linux/dma-direction.h>
#include <linux/gfp.h>
#include <linux/kmsan-checks.h>
#include <linux/stackdepot.h>
@@ -17,6 +18,7 @@
struct page;
struct kmem_cache;
struct task_struct;
+struct scatterlist;

#ifdef CONFIG_KMSAN

@@ -204,6 +206,35 @@ void kmsan_ioremap_page_range(unsigned long addr, unsigned long end,
*/
void kmsan_iounmap_page_range(unsigned long start, unsigned long end);

+/**
+ * kmsan_handle_dma() - Handle a DMA data transfer.
+ * @page: first page of the buffer.
+ * @offset: offset of the buffer within the first page.
+ * @size: buffer size.
+ * @dir: one of possible dma_data_direction values.
+ *
+ * Depending on @direction, KMSAN:
+ * * checks the buffer, if it is copied to device;
+ * * initializes the buffer, if it is copied from device;
+ * * does both, if this is a DMA_BIDIRECTIONAL transfer.
+ */
+void kmsan_handle_dma(struct page *page, size_t offset, size_t size,
+ enum dma_data_direction dir);
+
+/**
+ * kmsan_handle_dma_sg() - Handle a DMA transfer using scatterlist.
+ * @sg: scatterlist holding DMA buffers.
+ * @nents: number of scatterlist entries.
+ * @dir: one of possible dma_data_direction values.
+ *
+ * Depending on @direction, KMSAN:
+ * * checks the buffers in the scatterlist, if they are copied to device;
+ * * initializes the buffers, if they are copied from device;
+ * * does both, if this is a DMA_BIDIRECTIONAL transfer.
+ */
+void kmsan_handle_dma_sg(struct scatterlist *sg, int nents,
+ enum dma_data_direction dir);
+
#else

static inline void kmsan_init_shadow(void)
@@ -286,6 +317,16 @@ static inline void kmsan_iounmap_page_range(unsigned long start,
{
}

+static inline void kmsan_handle_dma(struct page *page, size_t offset,
+ size_t size, enum dma_data_direction dir)
+{
+}
+
+static inline void kmsan_handle_dma_sg(struct scatterlist *sg, int nents,
+ enum dma_data_direction dir)
+{
+}
+
#endif

#endif /* _LINUX_KMSAN_H */
diff --git a/kernel/dma/mapping.c b/kernel/dma/mapping.c
index db7244291b745..5d17d5d62166b 100644
--- a/kernel/dma/mapping.c
+++ b/kernel/dma/mapping.c
@@ -156,6 +156,7 @@ dma_addr_t dma_map_page_attrs(struct device *dev, struct page *page,
addr = dma_direct_map_page(dev, page, offset, size, dir, attrs);
else
addr = ops->map_page(dev, page, offset, size, dir, attrs);
+ kmsan_handle_dma(page, offset, size, dir);
debug_dma_map_page(dev, page, offset, size, dir, addr, attrs);

return addr;
@@ -194,11 +195,13 @@ static int __dma_map_sg_attrs(struct device *dev, struct scatterlist *sg,
else
ents = ops->map_sg(dev, sg, nents, dir, attrs);

- if (ents > 0)
+ if (ents > 0) {
+ kmsan_handle_dma_sg(sg, nents, dir);
debug_dma_map_sg(dev, sg, nents, ents, dir, attrs);
- else if (WARN_ON_ONCE(ents != -EINVAL && ents != -ENOMEM &&
- ents != -EIO))
+ } else if (WARN_ON_ONCE(ents != -EINVAL && ents != -ENOMEM &&
+ ents != -EIO)) {
return -EIO;
+ }

return ents;
}
diff --git a/mm/kmsan/hooks.c b/mm/kmsan/hooks.c
index 1cdb4420977f1..8a6947a2a2f22 100644
--- a/mm/kmsan/hooks.c
+++ b/mm/kmsan/hooks.c
@@ -10,9 +10,11 @@
*/

#include <linux/cacheflush.h>
+#include <linux/dma-direction.h>
#include <linux/gfp.h>
#include <linux/mm.h>
#include <linux/mm_types.h>
+#include <linux/scatterlist.h>
#include <linux/slab.h>
#include <linux/uaccess.h>

@@ -250,6 +252,65 @@ void kmsan_copy_to_user(void __user *to, const void *from, size_t to_copy,
}
EXPORT_SYMBOL(kmsan_copy_to_user);

+static void kmsan_handle_dma_page(const void *addr, size_t size,
+ enum dma_data_direction dir)
+{
+ switch (dir) {
+ case DMA_BIDIRECTIONAL:
+ kmsan_internal_check_memory((void *)addr, size, /*user_addr*/ 0,
+ REASON_ANY);
+ kmsan_internal_unpoison_memory((void *)addr, size,
+ /*checked*/ false);
+ break;
+ case DMA_TO_DEVICE:
+ kmsan_internal_check_memory((void *)addr, size, /*user_addr*/ 0,
+ REASON_ANY);
+ break;
+ case DMA_FROM_DEVICE:
+ kmsan_internal_unpoison_memory((void *)addr, size,
+ /*checked*/ false);
+ break;
+ case DMA_NONE:
+ break;
+ }
+}
+
+/* Helper function to handle DMA data transfers. */
+void kmsan_handle_dma(struct page *page, size_t offset, size_t size,
+ enum dma_data_direction dir)
+{
+ u64 page_offset, to_go, addr;
+
+ if (PageHighMem(page))
+ return;
+ addr = (u64)page_address(page) + offset;
+ /*
+ * The kernel may occasionally give us adjacent DMA pages not belonging
+ * to the same allocation. Process them separately to avoid triggering
+ * internal KMSAN checks.
+ */
+ while (size > 0) {
+ page_offset = addr % PAGE_SIZE;
+ to_go = min(PAGE_SIZE - page_offset, (u64)size);
+ kmsan_handle_dma_page((void *)addr, to_go, dir);
+ addr += to_go;
+ size -= to_go;
+ }
+}
+EXPORT_SYMBOL(kmsan_handle_dma);
+
+void kmsan_handle_dma_sg(struct scatterlist *sg, int nents,
+ enum dma_data_direction dir)
+{
+ struct scatterlist *item;
+ int i;
+
+ for_each_sg(sg, item, nents, i)
+ kmsan_handle_dma(sg_page(item), item->offset, item->length,
+ dir);
+}
+EXPORT_SYMBOL(kmsan_handle_dma_sg);
+
/* Functions from kmsan-checks.h follow. */
void kmsan_poison_memory(const void *address, size_t size, gfp_t flags)
{
--
2.37.0.rc0.161.g10f37bed90-goog