Re: [PATCH 5/5] remoteproc: core: Clip carveout if it's too big

[Bjorn Andersson <bjorn.andersson@linaro.org>]

On Thu 05 May 06:29 PDT 2016, Lee Jones wrote:

> Carveout size is primarily extracted from the firmware binary.  However,
> DT can over-ride this by providing a different (smaller) size.  We're
> adding protection here to ensure the we only allocate the smaller of the
> two provided sizes in order to decrease the risk of clashes.
> 

Is this really the right thing to do?

The firmware is bundled with a resource table stating a certain size of
this the carveout and this would "silently" give it less space. On some
systems an IOMMU will save us (killing the firmware) but on others I
fear the firmware might just access memory outside its expected buffer.

> Signed-off-by: Lee Jones <lee.jones@linaro.org>
> ---
>  drivers/remoteproc/remoteproc_core.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/drivers/remoteproc/remoteproc_core.c b/drivers/remoteproc/remoteproc_core.c
[..]
> @@ -600,6 +601,14 @@ static int rproc_handle_carveout(struct rproc *rproc,
>  		return -ENOMEM;
>  
>  	dma_dev = rproc_subdev_lookup(rproc, "carveout");
> +	sub = dev_get_drvdata(dma_dev);
> +
> +	if (rsc->len > resource_size(sub->res)) {
> +		dev_warn(dev, "carveout too big (0x%x): clipping to 0x%x\n",
> +			 rsc->len, resource_size(sub->res));
> +		rsc->len = resource_size(sub->res);
> +	}

I would rather expect this to say:

if (resource_size(sub->res) < rsc->len) {
	dev_err(dev, "defined carveout to small for firmware\n");
	return -EINVAL;
}

Unless we trust the remote firmware to dynamically follow what we put in
the resource table. (And how does it tell us if that limit isn't
enough?)

> +
>  	va = dma_alloc_coherent(dma_dev, rsc->len, &dma, GFP_KERNEL);
>  	if (!va) {
>  		dev_err(dev->parent, "dma_alloc_coherent err: %d\n", rsc->len);


Apart from this concern I'm still need to review the subdev patch; here
related the part that there's only room for one carveout with only one
size.

Regards,
Bjorn