v4.19.13 snapshot.
diff --git a/lib/check_signature.c b/lib/check_signature.c
new file mode 100644
index 0000000..43a7301
--- /dev/null
+++ b/lib/check_signature.c
@@ -0,0 +1,27 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/io.h>
+#include <linux/export.h>
+
+/**
+ * check_signature - find BIOS signatures
+ * @io_addr: mmio address to check
+ * @signature: signature block
+ * @length: length of signature
+ *
+ * Perform a signature comparison with the mmio address io_addr. This
+ * address should have been obtained by ioremap.
+ * Returns 1 on a match.
+ */
+
+int check_signature(const volatile void __iomem *io_addr,
+ const unsigned char *signature, int length)
+{
+ while (length--) {
+ if (readb(io_addr) != *signature)
+ return 0;
+ io_addr++;
+ signature++;
+ }
+ return 1;
+}
+EXPORT_SYMBOL(check_signature);