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-rw-r--r--tools/testing/selftests/arm64/gcs/gcsstr.S99
1 files changed, 99 insertions, 0 deletions
diff --git a/tools/testing/selftests/arm64/gcs/gcsstr.S b/tools/testing/selftests/arm64/gcs/gcsstr.S
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+++ b/tools/testing/selftests/arm64/gcs/gcsstr.S
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+// SPDX-License-Identifier: GPL-2.0-only
+//
+// Copyright 2024 Arm Limited
+//
+// Give ourselves GCS write permissions then use them
+
+#include <asm/unistd.h>
+
+/* Shadow Stack/Guarded Control Stack interface */
+#define PR_GET_SHADOW_STACK_STATUS 74
+#define PR_SET_SHADOW_STACK_STATUS 75
+#define PR_LOCK_SHADOW_STACK_STATUS 76
+
+# define PR_SHADOW_STACK_ENABLE (1UL << 0)
+# define PR_SHADOW_STACK_WRITE (1UL << 1)
+# define PR_SHADOW_STACK_PUSH (1UL << 2)
+
+#define GCSPR_EL0 S3_3_C2_C5_1
+
+#define KSFT_SKIP 4
+
+.macro function name
+ .macro endfunction
+ .type \name, @function
+ .purgem endfunction
+ .endm
+\name:
+.endm
+
+// Print a single character x0 to stdout
+// Clobbers x0-x2,x8
+function putc
+ str x0, [sp, #-16]!
+
+ mov x0, #1 // STDOUT_FILENO
+ mov x1, sp
+ mov x2, #1
+ mov x8, #__NR_write
+ svc #0
+
+ add sp, sp, #16
+ ret
+endfunction
+.globl putc
+
+// Print a NUL-terminated string starting at address x0 to stdout
+// Clobbers x0-x3,x8
+function puts
+ mov x1, x0
+
+ mov x2, #0
+0: ldrb w3, [x0], #1
+ cbz w3, 1f
+ add x2, x2, #1
+ b 0b
+
+1: mov w0, #1 // STDOUT_FILENO
+ mov x8, #__NR_write
+ svc #0
+
+ ret
+endfunction
+.globl puts
+
+// Utility macro to print a literal string
+// Clobbers x0-x4,x8
+.macro puts string
+ .pushsection .rodata.str1.1, "aMS", @progbits, 1
+.L__puts_literal\@: .string "\string"
+ .popsection
+
+ ldr x0, =.L__puts_literal\@
+ bl puts
+.endm
+
+.globl _start
+function _start
+ // Run with GCS
+ mov x0, PR_SET_SHADOW_STACK_STATUS
+ mov x1, PR_SHADOW_STACK_ENABLE | PR_SHADOW_STACK_WRITE
+ mov x2, xzr
+ mov x3, xzr
+ mov x4, xzr
+ mov x5, xzr
+ mov x8, #__NR_prctl
+ svc #0
+ cbz x0, 1f
+ puts "Failed to enable GCS with write permission\n"
+ mov x0, #KSFT_SKIP
+ b 2f
+1:
+ mrs x0, GCSPR_EL0
+ sub x0, x0, #8
+ .inst 0xd91f1c01 // GCSSTR x1, x0
+
+ mov x0, #0
+2:
+ mov x8, #__NR_exit
+ svc #0