Re: [PATCH v4 1/2] dma-mapping: Add vmap checks to dma_map_single()

[Christoph Hellwig]

On Wed, Oct 30, 2019 at 10:18:49AM +0100, Greg Kroah-Hartman wrote:
> On Tue, Oct 29, 2019 at 02:34:22PM -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..54de3c496407 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 (dev_WARN_ONCE(dev, is_vmalloc_addr(ptr),
> > +			  "wanted %zu bytes mapped in vmalloc\n", size)) {
> > +		return DMA_MAPPING_ERROR;
> > +	}
> 
> That's a very odd error string, I know if I saw it for the first time, I
> would have no idea what it meant.  The USB message at least gives you a
> bit more context as to what went wrong and how to fix it.
> 
> How about something like "Memory is not DMA capabable, please fix the
> allocation of it to be correct", or "non-dma-able memory was attempted
> to be mapped, but this is impossible to to" or something else.

I've fixed the message to "rejecting DMA map of vmalloc memory" and
applied the patch.