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

[Greg Kroah-Hartman]

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.
> 
> [1] https://git.kernel.org/linus/3840c5b78803b2b6cc1ff820100a74a092c40cbb
> 
> 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.

Other than that minor nit, I have no objection to this series, thanks
for fixing this up!

greg k-h