1 files changed, 31 insertions, 26 deletions

diff --git a/arch/arm64/lib/clear_user.S b/arch/arm64/lib/clear_user.S
index aeafc03e961a..a5a5f5b97b17 100644
--- a/arch/arm64/lib/clear_user.S
+++ b/arch/arm64/lib/clear_user.S
@@ -1,13 +1,10 @@
 /* SPDX-License-Identifier: GPL-2.0-only */
 /*
- * Based on arch/arm/lib/clear_user.S
- *
- * Copyright (C) 2012 ARM Ltd.
+ * Copyright (C) 2021 Arm Ltd.
  */
-#include <linux/linkage.h>
 
+#include <linux/linkage.h>
 #include <asm/asm-uaccess.h>
-#include <asm/assembler.h>
 
 	.text
 
@@ -19,32 +16,40 @@
  *
  * Alignment fixed up by hardware.
  */
-ENTRY(__arch_clear_user)
-	mov	x2, x1			// save the size for fixup return
+
+	.p2align 4
+	// Alignment is for the loop, but since the prologue (including BTI)
+	// is also 16 bytes we can keep any padding outside the function
+SYM_FUNC_START(__arch_clear_user)
+	add	x2, x0, x1
 	subs	x1, x1, #8
 	b.mi	2f
 1:
-uao_user_alternative 9f, str, sttr, xzr, x0, 8
+USER(9f, sttr	xzr, [x0])
+	add	x0, 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
+	b.hi	1b
+USER(9f, sttr	xzr, [x2, #-8])
+	mov	x0, #0
+	ret
+
+2:	tbz	x1, #2, 3f
+USER(9f, sttr	wzr, [x0])
+USER(8f, sttr	wzr, [x2, #-4])
+	mov	x0, #0
+	ret
+
+3:	tbz	x1, #1, 4f
+USER(9f, sttrh	wzr, [x0])
+4:	tbz	x1, #0, 5f
+USER(7f, sttrb	wzr, [x2, #-1])
 5:	mov	x0, #0
 	ret
-ENDPROC(__arch_clear_user)
-EXPORT_SYMBOL(__arch_clear_user)
 
-	.section .fixup,"ax"
-	.align	2
-9:	mov	x0, x2			// return the original size
+	// Exception fixups
+7:	sub	x0, x2, #5	// Adjust for faulting on the final byte...
+8:	add	x0, x0, #4	// ...or the second word of the 4-7 byte case
+9:	sub	x0, x2, x0
 	ret
-	.previous
+SYM_FUNC_END(__arch_clear_user)
+EXPORT_SYMBOL(__arch_clear_user)