efi_loader: parameter checks CalculateCrc32()

Not checking the parameters may lead reading or writing from NULL.
Implement the parameter checks prescribed in the UEFI spec.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
diff --git a/lib/efi_loader/efi_boottime.c b/lib/efi_loader/efi_boottime.c
index d3f21f1..ce6ca06 100644
--- a/lib/efi_loader/efi_boottime.c
+++ b/lib/efi_loader/efi_boottime.c
@@ -2465,9 +2465,16 @@
 					       efi_uintn_t data_size,
 					       u32 *crc32_p)
 {
+	efi_status_t ret = EFI_SUCCESS;
+
 	EFI_ENTRY("%p, %zu", data, data_size);
+	if (!data || !data_size || !crc32_p) {
+		ret = EFI_INVALID_PARAMETER;
+		goto out;
+	}
 	*crc32_p = crc32(0, data, data_size);
-	return EFI_EXIT(EFI_SUCCESS);
+out:
+	return EFI_EXIT(ret);
 }
 
 /**