[PATCH] Fix data abort caused by mis-aligning fit data in

[Reuben Dowle]

Should I submit a new patch with the alignment set to 8 bytes? I would think a hard coded 8 bytes would not be the best solution, since not all architectures will need that much alignment. I suspect some would work with any alignment, and most 32-bit archs would be fine with 4-byte alignment.

Our released software is actually using a patch to align to 4096 bytes, but I knew that was unnecessarily large. I was not really sure what would be an appropriate value here, and took a guess at ARCH_DMA_MINALIGN when I cleaned it up for submitting upstream. Is there a better define to use?

I am also interested to know where the 8 byte alignment requirement is documented.

Reuben

> -----Original Message-----
> From: Tom Rini <trini at konsulko.com>
> Sent: Tuesday, 25 August 2020 2:27 am
> To: Reuben Dowle <reuben.dowle at 4rf.com>
> Cc: u-boot at lists.denx.de
> Subject: Re: [PATCH] Fix data abort caused by mis-aligning fit data in
> 
> On Fri, Jul 24, 2020 at 05:19:39AM +0000, Reuben Dowle wrote:
> 
> > Attempting to place device tree immediately after an image in memory
> > can lead to mis-aligned data accesses if that image size is not
> > divisible by the alignment requirements of the architecture.
> >
> > Data aborts caused by this were observed on a custom Marvel A388 based
> > system, where the image was a uboot FIT file. The total size varies
> > depending on the uboot device tree size, which does not always lead to
> correct alignment.
> >
> > Signed-off-by: Reuben Dowle <reuben.dowle at 4rf.com>
> > ---
> >  common/spl/spl_fit.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/common/spl/spl_fit.c b/common/spl/spl_fit.c index
> > 365104f..d221075 100644
> > --- a/common/spl/spl_fit.c
> > +++ b/common/spl/spl_fit.c
> > @@ -349,9 +349,9 @@ static int spl_fit_append_fdt(struct
> > spl_image_info *spl_image,
> >
> >  	/*
> >  	 * Use the address following the image as target address for the
> > -	 * device tree.
> > +	 * device tree. Ensure that address is appropriately aligned.
> >  	 */
> > -	image_info.load_addr = spl_image->load_addr + spl_image->size;
> > +	image_info.load_addr = ALIGN(spl_image->load_addr + spl_image-
> >size,
> > +ARCH_DMA_MINALIGN);
> >
> >  	/* Figure out which device tree the board wants to use */
> >  	node = spl_fit_get_image_node(fit, images, FIT_FDT_PROP,
> index++);
> 
> Sorry for the late reply here.  While we do need to ensure that the device
> tree is aligned, the documented alignment requirement for all platforms is 8
> byte, so we should document and use that here in case future platforms
> require a higher alignment.  Thanks!
> 
> --
> Tom