Re: [PATCH v2] dma-mapping: Move vmap address checks into dma_map_single()

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Fri, Oct 04, 2019 at 02:28:16PM -0700, Kees Cook wrote:
> As we've seen from USB and other areas, we need to always do runtime
> checks for DMA operating on memory regions that might be remapped. This
> moves the existing checks from USB into dma_map_single(), but leaves
> the slightly heavier checks as they are.
> 
> Suggested-by: Laura Abbott <labbott@redhat.com>
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
> v2: Only add is_vmalloc_addr()
> v1: https://lore.kernel.org/lkml/201910021341.7819A660@keescook
> ---
>  drivers/usb/core/hcd.c      | 8 +-------
>  include/linux/dma-mapping.h | 7 +++++++
>  2 files changed, 8 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/usb/core/hcd.c b/drivers/usb/core/hcd.c
> index f225eaa98ff8..281568d464f9 100644
> --- a/drivers/usb/core/hcd.c
> +++ b/drivers/usb/core/hcd.c
> @@ -1410,10 +1410,7 @@ int usb_hcd_map_urb_for_dma(struct usb_hcd *hcd, struct urb *urb,
>  		if (hcd->self.uses_pio_for_control)
>  			return ret;
>  		if (hcd_uses_dma(hcd)) {
> -			if (is_vmalloc_addr(urb->setup_packet)) {
> -				WARN_ONCE(1, "setup packet is not dma capable\n");
> -				return -EAGAIN;
> -			} else if (object_is_on_stack(urb->setup_packet)) {
> +			if (object_is_on_stack(urb->setup_packet)) {
>  				WARN_ONCE(1, "setup packet is on stack\n");
>  				return -EAGAIN;
>  			}
> @@ -1479,9 +1476,6 @@ int usb_hcd_map_urb_for_dma(struct usb_hcd *hcd, struct urb *urb,
>  					ret = -EAGAIN;
>  				else
>  					urb->transfer_flags |= URB_DMA_MAP_PAGE;
> -			} else if (is_vmalloc_addr(urb->transfer_buffer)) {
> -				WARN_ONCE(1, "transfer buffer not dma capable\n");
> -				ret = -EAGAIN;
>  			} else if (object_is_on_stack(urb->transfer_buffer)) {
>  				WARN_ONCE(1, "transfer buffer is on stack\n");
>  				ret = -EAGAIN;
> diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
> index 4a1c4fca475a..12dbd07f74f2 100644
> --- a/include/linux/dma-mapping.h
> +++ b/include/linux/dma-mapping.h
> @@ -583,6 +583,13 @@ 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 (WARN_ONCE(is_vmalloc_addr(ptr),
> +		      "%s %s: driver maps %lu bytes from vmalloc area\n",
> +		      dev ? dev_driver_string(dev) : "unknown driver",
> +		      dev ? dev_name(dev) : "unknown device", size))

If you use dev_warn() here you get all of that "unknown driver/device"
checking and handling set properly.  And it's in the "standard" format
that userspace tools know how to check.

thanks,

greg k-h
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