v4.19.13 snapshot.
diff --git a/arch/arm64/lib/clear_user.S b/arch/arm64/lib/clear_user.S
new file mode 100644
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+++ b/arch/arm64/lib/clear_user.S
@@ -0,0 +1,61 @@
+/*
+ * Based on arch/arm/lib/clear_user.S
+ *
+ * Copyright (C) 2012 ARM Ltd.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+#include <linux/linkage.h>
+
+#include <asm/asm-uaccess.h>
+
+ .text
+
+/* Prototype: int __arch_clear_user(void *addr, size_t sz)
+ * Purpose : clear some user memory
+ * Params : addr - user memory address to clear
+ * : sz - number of bytes to clear
+ * Returns : number of bytes NOT cleared
+ *
+ * Alignment fixed up by hardware.
+ */
+ENTRY(__arch_clear_user)
+ uaccess_enable_not_uao x2, x3, x4
+ mov x2, x1 // save the size for fixup return
+ subs x1, x1, #8
+ b.mi 2f
+1:
+uao_user_alternative 9f, str, sttr, xzr, x0, 8
+ subs x1, x1, #8
+ b.pl 1b
+2: adds x1, x1, #4
+ b.mi 3f
+uao_user_alternative 9f, str, sttr, wzr, x0, 4
+ sub x1, x1, #4
+3: adds x1, x1, #2
+ b.mi 4f
+uao_user_alternative 9f, strh, sttrh, wzr, x0, 2
+ sub x1, x1, #2
+4: adds x1, x1, #1
+ b.mi 5f
+uao_user_alternative 9f, strb, sttrb, wzr, x0, 0
+5: mov x0, #0
+ uaccess_disable_not_uao x2, x3
+ ret
+ENDPROC(__arch_clear_user)
+
+ .section .fixup,"ax"
+ .align 2
+9: mov x0, x2 // return the original size
+ ret
+ .previous