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

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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



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