Re: [PATCH v3 1/2] dma-mapping: Add vmap checks to dma_map_single()

From: Robin Murphy
Date: Fri Oct 11 2019 - 05:33:53 EST

On 2019-10-11 6:02 am, Greg Kroah-Hartman wrote:
On Thu, Oct 10, 2019 at 03:28:28PM -0700, Kees Cook wrote:
As we've seen from USB and other areas[1], we need to always do runtime
checks for DMA operating on memory regions that might be remapped. This
adds vmap checks (similar to those already in USB but missing in other
places) into dma_map_single() so all callers benefit from the checking.


Suggested-by: Laura Abbott <labbott@xxxxxxxxxx>
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
include/linux/dma-mapping.h | 6 ++++++
1 file changed, 6 insertions(+)

diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
index 4a1c4fca475a..ff4e91c66f44 100644
--- a/include/linux/dma-mapping.h
+++ b/include/linux/dma-mapping.h
@@ -583,6 +583,12 @@ static inline unsigned long dma_get_merge_boundary(struct device *dev)
static inline dma_addr_t dma_map_single_attrs(struct device *dev, void *ptr,
size_t size, enum dma_data_direction dir, unsigned long attrs)
+ /* DMA must never operate on areas that might be remapped. */
+ if (unlikely(is_vmalloc_addr(ptr))) {
+ dev_warn_once(dev, "bad map: %zu bytes in vmalloc\n", size);

Can we get a bit better error text here? In USB we were at least giving
people a hint as to what went wrong, "bad map" might not really make
that much sense to a USB developer as to what they needed to do to fix
this issue.

Agreed, something along the lines of "dma_map_single of vmalloc'ed buffer..." might be clearer. Also I'd be inclined to use dev_WARN_ONCE() to include a diagnostically-useful backtrace, as the existing USB code would.