On Fri, Jan 28, 2022 at 11:18:03AM -0600, Brijesh Singh wrote:

+static int get_derived_key(struct snp_guest_dev *snp_dev, struct snp_guest_request_ioctl *arg)
+{
+	struct snp_guest_crypto *crypto = snp_dev->crypto;
+	struct snp_derived_key_resp resp = {0};
+	struct snp_derived_key_req req = {0};
+	int rc, resp_len;
+	u8 buf[64+16]; /* Response data is 64 bytes and max authsize for GCM is 16 bytes */

verify_comment_style: Warning: No tail comments please:
 drivers/virt/coco/sevguest/sevguest.c:401 [+	u8 buf[64+16]; /* Response data is 64 bytes and max authsize for GCM is 16 bytes */]

+	if (!arg->req_data || !arg->resp_data)
+		return -EINVAL;
+
+	/* Copy the request payload from userspace */

That comment looks useless.

+	if (copy_from_user(&req, (void __user *)arg->req_data, sizeof(req)))
+		return -EFAULT;
+
+	/*
+	 * The intermediate response buffer is used while decrypting the
+	 * response payload. Make sure that it has enough space to cover the
+	 * authtag.
+	 */
+	resp_len = sizeof(resp.data) + crypto->a_len;
+	if (sizeof(buf) < resp_len)
+		return -ENOMEM;

That test can happen before the copy_from_user() above.

+
+	/* Issue the command to get the attestation report */

Also useless.

+	rc = handle_guest_request(snp_dev, SVM_VMGEXIT_GUEST_REQUEST, arg->msg_version,
+				  SNP_MSG_KEY_REQ, &req, sizeof(req), buf, resp_len,
+				  &arg->fw_err);
+	if (rc)
+		goto e_free;
+
+	/* Copy the response payload to userspace */

Ditto.

+	memcpy(resp.data, buf, sizeof(resp.data));
+	if (copy_to_user((void __user *)arg->resp_data, &resp, sizeof(resp)))
+		rc = -EFAULT;
+
+e_free:
+	memzero_explicit(buf, sizeof(buf));
+	memzero_explicit(&resp, sizeof(resp));

Those are allocated on stack, why are you clearing them?

+	return rc;
+}

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette