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Subject[patch 3/8] Text Edit Lock - i386
Interface to use for code patching : makes sure the page is writable
between calls to kernel_text_mark_rw() and kernel_text_unmark().

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
---
arch/i386/mm/init.c | 60 ++++++++++++++++++++++++++++++++----------
include/asm-i386/cacheflush.h | 9 ++++++
2 files changed, 56 insertions(+), 13 deletions(-)

Index: linux-2.6-lttng/arch/i386/mm/init.c
===================================================================
--- linux-2.6-lttng.orig/arch/i386/mm/init.c 2007-07-13 17:01:24.000000000 -0400
+++ linux-2.6-lttng/arch/i386/mm/init.c 2007-07-13 17:02:31.000000000 -0400
@@ -31,6 +31,7 @@
#include <linux/memory_hotplug.h>
#include <linux/initrd.h>
#include <linux/cpumask.h>
+#include <linux/kprobes.h>

#include <asm/processor.h>
#include <asm/system.h>
@@ -53,6 +54,10 @@

static int noinline do_test_wp_bit(void);

+#ifdef CONFIG_DEBUG_RODATA
+static int rodata_marked;
+#endif
+
/*
* Creates a middle page table and puts a pointer to it in the
* given global directory entry. This only returns the gd entry
@@ -796,24 +801,16 @@
}

#ifdef CONFIG_DEBUG_RODATA
-
void mark_rodata_ro(void)
{
unsigned long start = PFN_ALIGN(_text);
unsigned long size = PFN_ALIGN(_etext) - start;

-#ifndef CONFIG_KPROBES
-#ifdef CONFIG_HOTPLUG_CPU
- /* It must still be possible to apply SMP alternatives. */
- if (num_possible_cpus() <= 1)
-#endif
- {
- change_page_attr(virt_to_page(start),
- size >> PAGE_SHIFT, PAGE_KERNEL_RX);
- printk("Write protecting the kernel text: %luk\n", size >> 10);
- kernel_text_is_ro = 1;
- }
-#endif
+ change_page_attr(virt_to_page(start),
+ size >> PAGE_SHIFT, PAGE_KERNEL_RX);
+ printk("Write protecting the kernel text: %luk\n", size >> 10);
+ kernel_text_is_ro = 1;
+
start += size;
size = (unsigned long)__end_rodata - start;
change_page_attr(virt_to_page(start),
@@ -828,9 +825,46 @@
* of who is the culprit.
*/
global_flush_tlb();
+ rodata_marked = 1;
+}
+
+/*
+ * Lock the kernel text for mutual write exclusion.
+ * Make sure the pages are writable.
+ */
+void __kprobes kernel_text_mark_rw(unsigned long address, size_t len)
+{
+ if (rodata_marked && address >= PFN_ALIGN(_text)
+ && (address + len) <= PFN_ALIGN(_etext)) {
+ unsigned long nr_pages;
+ nr_pages = ((address + len) >> PAGE_SHIFT)
+ - (address >> PAGE_SHIFT) + 1;
+ change_page_attr(virt_to_page(address), nr_pages,
+ PAGE_KERNEL_EXEC);
+ mb();
+ global_flush_tlb();
+ mb();
+ }
}
+EXPORT_SYMBOL_GPL(kernel_text_mark_rw);
#endif

+void __kprobes kernel_text_unmark(unsigned long address, size_t len)
+{
+ if (rodata_marked && address >= PFN_ALIGN(_text)
+ && (address + len) <= PFN_ALIGN(_etext)) {
+ unsigned long nr_pages;
+ nr_pages = ((address + len) >> PAGE_SHIFT)
+ - (address >> PAGE_SHIFT) + 1;
+ change_page_attr(virt_to_page(address), nr_pages,
+ PAGE_KERNEL_RX);
+ mb();
+ global_flush_tlb();
+ mb();
+ }
+}
+EXPORT_SYMBOL_GPL(kernel_text_unmark);
+
void free_init_pages(char *what, unsigned long begin, unsigned long end)
{
unsigned long addr;
Index: linux-2.6-lttng/include/asm-i386/cacheflush.h
===================================================================
--- linux-2.6-lttng.orig/include/asm-i386/cacheflush.h 2007-07-13 17:01:24.000000000 -0400
+++ linux-2.6-lttng/include/asm-i386/cacheflush.h 2007-07-13 17:01:26.000000000 -0400
@@ -36,4 +36,13 @@
void mark_rodata_ro(void);
#endif

+#if defined(CONFIG_DEBUG_RODATA)
+/* mark kernel text pages writable */
+extern void kernel_text_mark_rw(unsigned long address, size_t len);
+extern void kernel_text_unmark(unsigned long address, size_t len);
+#else
+void kernel_text_mark_rw(unsigned long address, size_t len) { }
+void kernel_text_unmark(unsigned long address, size_t len) { }
+#endif
+
#endif /* _I386_CACHEFLUSH_H */
--
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
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