x86: add testcases for RODATA and NX protections/attributes

Latest update; I now have 4 NX tests, but 2 fail so they're #if 0'd.
I also cleaned up the NX test code quite a bit, and got rid of the ugly
exception table sorting stuff.

From: Arjan van de Ven <arjan@linux.intel.com>

This patch adds testcases for the CONFIG_DEBUG_RODATA configuration option
as well as the NX CPU feature/mappings. Both testcases can move to tests/
once that patch gets merged into mainline.
(I'm half considering moving the rodata test into mm/init.c but I'll
wait with that until init.c is unified)

As part of this I had to fix a not-quite-right alignment in the vmlinux.lds.h
for the RODATA sections, which lead to 1 page less being marked read only.

Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 86 insertions, 0 deletions

diff --git a/arch/x86/kernel/test_rodata.c b/arch/x86/kernel/test_rodata.c
new file mode 100644
index 000000000000..4c163772000e
--- /dev/null
+++ b/arch/x86/kernel/test_rodata.c
@@ -0,0 +1,86 @@
+/*
+ * test_rodata.c: functional test for mark_rodata_ro function
+ *
+ * (C) Copyright 2008 Intel Corporation
+ * Author: Arjan van de Ven <arjan@linux.intel.com>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; version 2
+ * of the License.
+ */
+#include <linux/module.h>
+#include <asm/sections.h>
+extern int rodata_test_data;
+
+int rodata_test(void)
+{
+	unsigned long result;
+	unsigned long start, end;
+
+	/* test 1: read the value */
+	/* If this test fails, some previous testrun has clobbered the state */
+	if (!rodata_test_data) {
+		printk(KERN_ERR "rodata_test: test 1 fails (start data)\n");
+		return -ENODEV;
+	}
+
+	/* test 2: write to the variable; this should fault */
+	/*
+	 * If this test fails, we managed to overwrite the data
+	 *
+	 * This is written in assembly to be able to catch the
+	 * exception that is supposed to happen in the correct
+	 * case
+	 */
+
+	result = 1;
+	asm volatile(
+		"0:	mov %[zero],(%[rodata_test])\n"
+		"	mov %[zero], %[rslt]\n"
+		"1:\n"
+		".section .fixup,\"ax\"\n"
+		"2:	jmp 1b\n"
+		".previous\n"
+		".section __ex_table,\"a\"\n"
+		"       .align 16\n"
+#ifdef CONFIG_X86_32
+		"	.long 0b,2b\n"
+#else
+		"	.quad 0b,2b\n"
+#endif
+		".previous"
+		: [rslt] "=r" (result)
+		: [rodata_test] "r" (&rodata_test_data), [zero] "r" (0UL)
+	);
+
+
+	if (!result) {
+		printk(KERN_ERR "rodata_test: test data was not read only\n");
+		return -ENODEV;
+	}
+
+	/* test 3: check the value hasn't changed */
+	/* If this test fails, we managed to overwrite the data */
+	if (!rodata_test_data) {
+		printk(KERN_ERR "rodata_test: Test 3 failes (end data)\n");
+		return -ENODEV;
+	}
+	/* test 4: check if the rodata section is 4Kb aligned */
+	start = (unsigned long)__start_rodata;
+	end = (unsigned long)__end_rodata;
+	if (start & (PAGE_SIZE - 1)) {
+		printk(KERN_ERR "rodata_test: .rodata is not 4k aligned\n");
+		return -ENODEV;
+	}
+	if (end & (PAGE_SIZE - 1)) {
+		printk(KERN_ERR "rodata_test: .rodata end is not 4k aligned\n");
+		return -ENODEV;
+	}
+
+	return 0;
+}
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("Testcase for the DEBUG_RODATA infrastructure");
+MODULE_AUTHOR("Arjan van de Ven <arjan@linux.intel.com>");