linux-kernel - Re: [PATCH v4 1/2] dma-mapping: Add vmap checks to dma_map

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Message-ID: <20191030180921.GB19366@lst.de>
Date:   Wed, 30 Oct 2019 19:09:21 +0100
From:   Christoph Hellwig <hch@....de>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Kees Cook <keescook@...omium.org>, Christoph Hellwig <hch@....de>,
        Robin Murphy <robin.murphy@....com>,
        Laura Abbott <labbott@...hat.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Allison Randal <allison@...utok.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Stephen Boyd <swboyd@...omium.org>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Semmle Security Reports <security-reports@...mle.com>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 1/2] dma-mapping: Add vmap checks to dma_map_single()

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@...hat.com>
> > Signed-off-by: Kees Cook <keescook@...omium.org>
> > ---
> >  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.