Re: [PATCH v2 8/9] platform/surface: Add Surface Aggregator user-space interface

[Maximilian Luz]

On 12/15/20 5:35 PM, Hans de Goede wrote:
> Hi,
>
> On 12/3/20 10:26 PM, Maximilian Luz wrote:
> > Add a misc-device providing user-space access to the Surface Aggregator
> > EC, mainly intended for debugging, testing, and reverse-engineering.
> > This interface gives user-space applications the ability to send
> > requests to the EC and receive the corresponding responses.
> >
> > The device-file is managed by a pseudo platform-device and corresponding
> > driver to avoid dependence on the dedicated bus, allowing it to be
> > loaded in a minimal configuration.
> >
> > Signed-off-by: Maximilian Luz <luzmaximilian@xxxxxxxxx>
>
> 1 review comment inline:

[...]

> > +static long ssam_cdev_request(struct ssam_cdev *cdev, unsigned long arg)
> > +{
> > +	struct ssam_cdev_request __user *r;
> > +	struct ssam_cdev_request rqst;
> > +	struct ssam_request spec;
> > +	struct ssam_response rsp;
> > +	const void __user *plddata;
> > +	void __user *rspdata;
> > +	int status = 0, ret = 0, tmp;
> > +
> > +	r = (struct ssam_cdev_request __user *)arg;
> > +	ret = copy_struct_from_user(&rqst, sizeof(rqst), r, sizeof(*r));
> > +	if (ret)
> > +		goto out;
> > +
> > +	plddata = u64_to_user_ptr(rqst.payload.data);
> > +	rspdata = u64_to_user_ptr(rqst.response.data);
> > +
> > +	/* Setup basic request fields. */
> > +	spec.target_category = rqst.target_category;
> > +	spec.target_id = rqst.target_id;
> > +	spec.command_id = rqst.command_id;
> > +	spec.instance_id = rqst.instance_id;
> > +	spec.flags = rqst.flags;
> > +	spec.length = rqst.payload.length;
> > +	spec.payload = NULL;
> > +
> > +	rsp.capacity = rqst.response.length;
> > +	rsp.length = 0;
> > +	rsp.pointer = NULL;
> > +
> > +	/* Get request payload from user-space. */
> > +	if (spec.length) {
> > +		if (!plddata) {
> > +			ret = -EINVAL;
> > +			goto out;
> > +		}
> > +
> > +		spec.payload = kzalloc(spec.length, GFP_KERNEL);
> > +		if (!spec.payload) {
> > +			status = -ENOMEM;
> > +			ret = -EFAULT;
> > +			goto out;
> > +		}
> > +
> > +		if (copy_from_user((void *)spec.payload, plddata, spec.length)) {
> > +			ret = -EFAULT;
> > +			goto out;
> > +		}
> > +	}
> > +
> > +	/* Allocate response buffer. */
> > +	if (rsp.capacity) {
> > +		if (!rspdata) {
> > +			ret = -EINVAL;
> > +			goto out;
> > +		}
> > +
> > +		rsp.pointer = kzalloc(rsp.capacity, GFP_KERNEL);
> > +		if (!rsp.pointer) {
> > +			status = -ENOMEM;
> > +			ret = -EFAULT;
>
> This is weird, -EFAULT should only be used if a SEGFAULT
> would have been raised if the code was running in
> userspace rather then in kernelspace, IOW if userspace
> has provided an invalid pointer (or a too small buffer,
> causing the pointer to become invalid at some point in
> the buffer).

Oh, right.

> IMHO you should simply do ret = -ENOMEM here.

Yes. that looks better. I will change that as suggested.
> Otherwise this looks good to me.

Thanks,
Max