misc: amd-sbi: Address copy_to/from_user() warning reported in smatch

Smatch warnings are reported for below commit,

Commit bb13a84 ("misc: amd-sbi: Add support for CPUID protocol")
from Apr 28, 2025 (linux-next), leads to the following Smatch static
checker warning:

drivers/misc/amd-sbi/rmi-core.c:376 apml_rmi_reg_xfer() warn: maybe return -EFAULT instead of the bytes remaining?
drivers/misc/amd-sbi/rmi-core.c:394 apml_mailbox_xfer() warn: maybe return -EFAULT instead of the bytes remaining?
drivers/misc/amd-sbi/rmi-core.c:411 apml_cpuid_xfer() warn: maybe return -EFAULT instead of the bytes remaining?
drivers/misc/amd-sbi/rmi-core.c:428 apml_mcamsr_xfer() warn: maybe return -EFAULT instead of the bytes remaining?

copy_to/from_user() returns number of bytes, not copied.
In case data not copied, return "-EFAULT".
Additionally, fixes the "-EPROTOTYPE" error return as intended.

Fixes: 35ac203 ("misc: amd-sbi: Add support for AMD_SBI IOCTL")
Fixes: bb13a84 ("misc: amd-sbi: Add support for CPUID protocol")
Fixes: 69b1ba8 ("misc: amd-sbi: Add support for read MCA register protocol")
Fixes: cf14128 ("misc: amd-sbi: Add support for register xfer")
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Closes: https://lore.kernel.org/all/aDVyO8ByVsceybk9@stanley.mountain/
Reviewed-by: Naveen Krishna Chatradhi <naveenkrishna.chatradhi@amd.com>
Signed-off-by: Akshay Gupta <akshay.gupta@amd.com>
Link: https://lore.kernel.org/r/20250716110729.2193725-2-akshay.gupta@amd.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: akky16

drivers/misc/amd-sbi/rmi-core.c

@@ -372,7 +372,8 @@ static int apml_rmi_reg_xfer(struct sbrmi_data *data,
 	mutex_unlock(&data->lock);
 
 	if (msg.rflag && !ret)
-		return copy_to_user(arg, &msg, sizeof(struct apml_reg_xfer_msg));
+		if (copy_to_user(arg, &msg, sizeof(struct apml_reg_xfer_msg)))
+			return -EFAULT;
 	return ret;
 }
 
@@ -390,7 +391,9 @@ static int apml_mailbox_xfer(struct sbrmi_data *data, struct apml_mbox_msg __use
 	if (ret && ret != -EPROTOTYPE)
 		return ret;
 
-	return copy_to_user(arg, &msg, sizeof(struct apml_mbox_msg));
+	if (copy_to_user(arg, &msg, sizeof(struct apml_mbox_msg)))
+		return -EFAULT;
+	return ret;
 }
 
 static int apml_cpuid_xfer(struct sbrmi_data *data, struct apml_cpuid_msg __user *arg)
@@ -407,7 +410,9 @@ static int apml_cpuid_xfer(struct sbrmi_data *data, struct apml_cpuid_msg __user
 	if (ret && ret != -EPROTOTYPE)
 		return ret;
 
-	return copy_to_user(arg, &msg, sizeof(struct apml_cpuid_msg));
+	if (copy_to_user(arg, &msg, sizeof(struct apml_cpuid_msg)))
+		return -EFAULT;
+	return ret;
 }
 
 static int apml_mcamsr_xfer(struct sbrmi_data *data, struct apml_mcamsr_msg __user *arg)
@@ -424,7 +429,9 @@ static int apml_mcamsr_xfer(struct sbrmi_data *data, struct apml_mcamsr_msg __us
 	if (ret && ret != -EPROTOTYPE)
 		return ret;
 
-	return copy_to_user(arg, &msg, sizeof(struct apml_mcamsr_msg));
+	if (copy_to_user(arg, &msg, sizeof(struct apml_mcamsr_msg)))
+		return -EFAULT;
+	return ret;
 }
 
 static long sbrmi_ioctl(struct file *fp, unsigned int cmd, unsigned long arg)