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>
diff --git a/arch/x86/kernel/test_nx.c b/arch/x86/kernel/test_nx.c
new file mode 100644
index 0000000..6d7ef11
--- /dev/null
+++ b/arch/x86/kernel/test_nx.c
@@ -0,0 +1,176 @@
+/*
+ * test_nx.c: functional test for NX functionality
+ *
+ * (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 <linux/sort.h>
+#include <asm/uaccess.h>
+
+extern int rodata_test_data;
+
+/*
+ * This file checks 4 things:
+ * 1) Check if the stack is not executable
+ * 2) Check if kmalloc memory is not executable
+ * 3) Check if the .rodata section is not executable
+ * 4) Check if the .data section of a module is not executable
+ *
+ * To do this, the test code tries to execute memory in stack/kmalloc/etc,
+ * and then checks if the expected trap happens.
+ *
+ * Sadly, this implies having a dynamic exception handling table entry.
+ * ... which can be done (and will make Rusty cry)... but it can only
+ * be done in a stand-alone module with only 1 entry total.
+ * (otherwise we'd have to sort and that's just too messy)
+ */
+
+
+
+/*
+ * We want to set up an exception handling point on our stack,
+ * which means a variable value. This function is rather dirty
+ * and walks the exception table of the module, looking for a magic
+ * marker and replaces it with a specific function.
+ */
+static void fudze_exception_table(void *marker, void *new)
+{
+ struct module *mod = THIS_MODULE;
+ struct exception_table_entry *extable;
+
+ /*
+ * Note: This module has only 1 exception table entry,
+ * so searching and sorting is not needed. If that changes,
+ * this would be the place to search and re-sort the exception
+ * table.
+ */
+ if (mod->num_exentries > 1) {
+ printk(KERN_ERR "test_nx: too many exception table entries!\n");
+ printk(KERN_ERR "test_nx: test results are not reliable.\n");
+ return;
+ }
+ extable = (struct exception_table_entry *)mod->extable;
+ extable[0].insn = (unsigned long)new;
+}
+
+
+/*
+ * exception tables get their symbols translated so we need
+ * to use a fake function to put in there, which we can then
+ * replace at runtime.
+ */
+void foo_label(void);
+
+/*
+ * returns 0 for not-executable, negative for executable
+ *
+ * Note: we cannot allow this function to be inlined, because
+ * that would give us more than 1 exception table entry.
+ * This in turn would break the assumptions above.
+ */
+static noinline int test_address(void *address)
+{
+ unsigned long result;
+
+ /* Set up an exception table entry for our address */
+ fudze_exception_table(&foo_label, address);
+ result = 1;
+ asm volatile(
+ "foo_label:\n"
+ "0: call *%[fake_code]\n"
+ "1:\n"
+ ".section .fixup,\"ax\"\n"
+ "2: mov %[zero], %[rslt]\n"
+ " ret\n"
+ ".previous\n"
+ ".section __ex_table,\"a\"\n"
+ " .align 8\n"
+ " .quad 0b\n"
+ " .quad 2b\n"
+ ".previous\n"
+ : [rslt] "=r" (result)
+ : [fake_code] "r" (address), [zero] "r" (0UL), "0" (result)
+ );
+ /* change the exception table back for the next round */
+ fudze_exception_table(address, &foo_label);
+
+ if (result)
+ return -ENODEV;
+ return 0;
+}
+
+static unsigned char test_data = 0xC3; /* 0xC3 is the opcode for "ret" */
+
+static int test_NX(void)
+{
+ int ret = 0;
+ /* 0xC3 is the opcode for "ret" */
+ char stackcode[] = {0xC3, 0x90, 0 };
+ char *heap;
+
+ test_data = 0xC3;
+
+ printk(KERN_INFO "Testing NX protection\n");
+
+ /* Test 1: check if the stack is not executable */
+ if (test_address(&stackcode)) {
+ printk(KERN_ERR "test_nx: stack was executable\n");
+ ret = -ENODEV;
+ }
+
+
+ /* Test 2: Check if the heap is executable */
+ heap = kmalloc(64, GFP_KERNEL);
+ if (!heap)
+ return -ENOMEM;
+ heap[0] = 0xC3; /* opcode for "ret" */
+
+ if (test_address(heap)) {
+ printk(KERN_ERR "test_nx: heap was executable\n");
+ ret = -ENODEV;
+ }
+ kfree(heap);
+
+ /*
+ * The following 2 tests currently fail, this needs to get fixed
+ * Until then, don't run them to avoid too many people getting scared
+ * by the error message
+ */
+#if 0
+
+#ifdef CONFIG_DEBUG_RODATA
+ /* Test 3: Check if the .rodata section is executable */
+ if (rodata_test_data != 0xC3) {
+ printk(KERN_ERR "test_nx: .rodata marker has invalid value\n");
+ ret = -ENODEV;
+ } else if (test_address(&rodata_test_data)) {
+ printk(KERN_ERR "test_nx: .rodata section is executable\n");
+ ret = -ENODEV;
+ }
+#endif
+
+ /* Test 4: Check if the .data section of a module is executable */
+ if (test_address(&test_data)) {
+ printk(KERN_ERR "test_nx: .data section is executable\n");
+ ret = -ENODEV;
+ }
+
+#endif
+ return 0;
+}
+
+static void test_exit(void)
+{
+}
+
+module_init(test_NX);
+module_exit(test_exit);
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("Testcase for the NX infrastructure");
+MODULE_AUTHOR("Arjan van de Ven <arjan@linux.intel.com>");
diff --git a/arch/x86/kernel/test_rodata.c b/arch/x86/kernel/test_rodata.c
new file mode 100644
index 0000000..4c16377
--- /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>");
diff --git a/arch/x86/mm/init_32.c b/arch/x86/mm/init_32.c
index 4d11565..a72737c 100644
--- a/arch/x86/mm/init_32.c
+++ b/arch/x86/mm/init_32.c
@@ -736,6 +736,8 @@
}
#ifdef CONFIG_DEBUG_RODATA
+const int rodata_test_data = 0xC3;
+EXPORT_SYMBOL_GPL(rodata_test_data);
void mark_rodata_ro(void)
{
@@ -765,6 +767,7 @@
set_pages_ro(virt_to_page(start), size >> PAGE_SHIFT);
printk("Write protecting the kernel read-only data: %luk\n",
size >> 10);
+ rodata_test();
#ifdef CONFIG_CPA_DEBUG
printk("Testing CPA: undo %lx-%lx\n", start, start + size);
diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
index f97ace7..50d29f5 100644
--- a/arch/x86/mm/init_64.c
+++ b/arch/x86/mm/init_64.c
@@ -573,6 +573,7 @@
set_memory_rw(begin, (end - begin)/PAGE_SIZE);
set_memory_np(begin, (end - begin)/PAGE_SIZE);
set_memory_nx(begin, (end - begin)/PAGE_SIZE);
+ rodata_test();
}
#endif
}
@@ -585,6 +586,8 @@
}
#ifdef CONFIG_DEBUG_RODATA
+const int rodata_test_data = 0xC3;
+EXPORT_SYMBOL_GPL(rodata_test_data);
void mark_rodata_ro(void)
{
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 76df771..f784d2f 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -184,6 +184,7 @@
VMLINUX_SYMBOL(__start___param) = .; \
*(__param) \
VMLINUX_SYMBOL(__stop___param) = .; \
+ . = ALIGN((align)); \
VMLINUX_SYMBOL(__end_rodata) = .; \
} \
. = ALIGN((align));
diff --git a/include/asm-x86/cacheflush.h b/include/asm-x86/cacheflush.h
index 157da02..3e74aff 100644
--- a/include/asm-x86/cacheflush.h
+++ b/include/asm-x86/cacheflush.h
@@ -47,5 +47,12 @@
#ifdef CONFIG_DEBUG_RODATA
void mark_rodata_ro(void);
#endif
+#ifdef CONFIG_DEBUG_RODATA_TEST
+void rodata_test(void);
+#else
+static inline void rodata_test(void)
+{
+}
+#endif
#endif