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-rw-r--r--arch/arm64/lib/clear_user.S47
1 files changed, 27 insertions, 20 deletions
diff --git a/arch/arm64/lib/clear_user.S b/arch/arm64/lib/clear_user.S
index af9afcbec92c..a7efb2ad2a1c 100644
--- a/arch/arm64/lib/clear_user.S
+++ b/arch/arm64/lib/clear_user.S
@@ -1,12 +1,9 @@
/* 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 <asm/asm-uaccess.h>
+#include <linux/linkage.h>
#include <asm/assembler.h>
.text
@@ -19,25 +16,33 @@
*
* Alignment fixed up by hardware.
*/
+
+ .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)
- mov x2, x1 // save the size for fixup return
+ add x2, x0, x1
subs x1, x1, #8
b.mi 2f
1:
-user_ldst 9f, 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
-user_ldst 9f, sttr, wzr, x0, 4
- sub x1, x1, #4
-3: adds x1, x1, #2
- b.mi 4f
-user_ldst 9f, sttrh, wzr, x0, 2
- sub x1, x1, #2
-4: adds x1, x1, #1
- b.mi 5f
-user_ldst 9f, 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
SYM_FUNC_END(__arch_clear_user)
@@ -45,6 +50,8 @@ EXPORT_SYMBOL(__arch_clear_user)
.section .fixup,"ax"
.align 2
-9: mov x0, x2 // return the original size
+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
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