Subject: [PATCH v3] pxa2xx_spi: fix memory corruption

From: [email-masked] (Vasily Khoruzhick)
Date: Mon, 18 Jul 2011 10:56:51 +0300

On Friday 15 July 2011 05:53:31 Grant Likely wrote:
> On Sun, Jul 10, 2011 at 06:18:19PM +0300, Vasily Khoruzhick wrote:
> > pxa2xx_spi_probe allocates struct driver_data and null_dma_buf
> > at same time via spi_alloc_master(), but then calculates
> > null_dma_buf pointer incorrectly, and it causes memory corruption
> > later if DMA usage is enabled.
> > 
> > Signed-off-by: Vasily Khoruzhick <[email-masked]>
> > ---
> > v2: - add u8 __null_dma_buf[16] to the end of driver_data structure
> > 
> >     and use it as null_dma_buf after alignment.
> >     - use PTR_ALIGN instead of ALIGN
> > 
> > v3: - drop (u8 *) cast, use & operator instead, change array name
> > 
> >  drivers/spi/pxa2xx_spi.c |    9 +++++----
> >  1 files changed, 5 insertions(+), 4 deletions(-)
> > 
> > diff --git a/drivers/spi/pxa2xx_spi.c b/drivers/spi/pxa2xx_spi.c
> > index dc25bee..b25fe27 100644
> > --- a/drivers/spi/pxa2xx_spi.c
> > +++ b/drivers/spi/pxa2xx_spi.c
> > @@ -106,6 +106,7 @@ struct driver_data {
> > 
> >  	int rx_channel;
> >  	int tx_channel;
> >  	u32 *null_dma_buf;
> > 
> > +	u8 null_dma_buf_unaligned[16];
> 
> Don't dma buffers need to be cache-line aligned? 

No, on PXA2xx they need to be 8-bytes aligned (according to PXA27x developer's 
manual)

> How large is the actual transfer?

Looks like 8 bytes, but I'm not sure, I'm not author of driver and did not dig 
deeply into its code. Just attempting to fix memory corruption.

> Using the __aligned() or __cacheline_aligned
> attribute is the correct way to make sure you've got a data buffer
> that can be used for DMA mixed with other stuff.  Then you don't need
> to fool around with PTR_ALIGN or anything.

Errr, it can't be applied to struct field, right? But driver needs per-device 
null_dma_buf (there's 3 SPI controllers on PXA2xx)

> g.

Regards
Vasily