Re: [PATCH V10 06/12] of: device: Fix overflow of coherent_dma_mask

[Sricharan R]

Hi Frank,

On 4/6/2017 12:31 PM, Frank Rowand wrote:
> On 04/04/17 03:18, Sricharan R wrote:
> > Size of the dma-range is calculated as coherent_dma_mask + 1
> > and passed to arch_setup_dma_ops further. It overflows when
> > the coherent_dma_mask is set for full 64 bits 0xFFFFFFFFFFFFFFFF,
> > resulting in size getting passed as 0 wrongly. Fix this by
> > passsing in max(mask, mask + 1). Note that in this case
> > when the mask is set to full 64bits, we will be passing the mask
> > itself to arch_setup_dma_ops instead of the size. The real fix
> > for this should be to make arch_setup_dma_ops receive the
> > mask and handle it, to be done in the future.
> >
> > Signed-off-by: Sricharan R <sricharan@xxxxxxxxxxxxxx>
> > ---
> >  drivers/of/device.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/of/device.c b/drivers/of/device.c
> > index c17c19d..c2ae6bb 100644
> > --- a/drivers/of/device.c
> > +++ b/drivers/of/device.c
> > @@ -107,7 +107,7 @@ void of_dma_configure(struct device *dev, struct device_node *np)
> >  	ret = of_dma_get_range(np, &dma_addr, &paddr, &size);
> >  	if (ret < 0) {
> >  		dma_addr = offset = 0;
> > -		size = dev->coherent_dma_mask + 1;
> > +		size = max(dev->coherent_dma_mask, dev->coherent_dma_mask + 1);
> >  	} else {
> >  		offset = PFN_DOWN(paddr - dma_addr);
> >  		dev_dbg(dev, "dma_pfn_offset(%#08lx)\n", offset);
>
> NACK.
>
> Passing an invalid size to arch_setup_dma_ops() is only part of the problem.
> size is also used in of_dma_configure() before calling arch_setup_dma_ops():
>
>         dev->coherent_dma_mask = min(dev->coherent_dma_mask,
>                                      DMA_BIT_MASK(ilog2(dma_addr + size)));
>         *dev->dma_mask = min((*dev->dma_mask),
>                              DMA_BIT_MASK(ilog2(dma_addr + size)));
>
> which would be incorrect for size == 0xffffffffffffffffULL when
> dma_addr != 0.  So the proposed fix really is not papering over
> the base problem very well.

Ok, but with your fix for of_dma_get_range and the above fix,
dma_addr will be '0' when size = 0xffffffffffffffffULL,
but DMA_BIT_MASK(ilog2(dma_addr + size)) would be wrong though,
making coherent_dma_mask to be smaller 0x7fffffffffffffffULL.

Regards,
 Sricharan

> I agree that the proper solution involves passing a mask instead
> of a size to arch_setup_dma_ops().

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