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Subject[patch 4/8] Text Edit Lock - x86_64
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>
CC: Andi Kleen <andi@firstfloor.org>
---
arch/x86_64/mm/init.c | 64 +++++++++++++++++++++++++++-------------
include/asm-x86_64/cacheflush.h | 9 +++++
2 files changed, 53 insertions(+), 20 deletions(-)
Index: linux-2.6-lttng/arch/x86_64/mm/init.c
===================================================================
--- linux-2.6-lttng.orig/arch/x86_64/mm/init.c 2007-07-13 16:08:14.000000000 -0400
+++ linux-2.6-lttng/arch/x86_64/mm/init.c 2007-07-13 16:36:40.000000000 -0400
@@ -56,6 +56,10 @@

DEFINE_PER_CPU(struct mmu_gather, mmu_gathers);

+#ifdef CONFIG_DEBUG_RODATA
+static int rodata_marked;
+#endif
+
/*
* NOTE: pagetable_init alloc all the fixmap pagetables contiguous on the
* physical space so we can cache the place of the first one and move
@@ -596,31 +600,15 @@
}

#ifdef CONFIG_DEBUG_RODATA
-
void mark_rodata_ro(void)
{
- unsigned long start = (unsigned long)_stext, end;
+ unsigned long start = PFN_ALIGN(_stext);
+ unsigned long end = PFN_ALIGN(__end_rodata);

kernel_text_is_ro = 1;
-#ifdef CONFIG_HOTPLUG_CPU
- /* It must still be possible to apply SMP alternatives. */
- if (num_possible_cpus() > 1) {
- start = (unsigned long)_etext;
- kernel_text_is_ro = 0;
- }
-#endif

-#ifdef CONFIG_KPROBES
- start = (unsigned long)__start_rodata;
-#endif
-
- end = (unsigned long)__end_rodata;
- start = (start + PAGE_SIZE - 1) & PAGE_MASK;
- end &= PAGE_MASK;
- if (end <= start)
- return;
-
- change_page_attr_addr(start, (end - start) >> PAGE_SHIFT, PAGE_KERNEL_RO);
+ change_page_attr_addr(start, (end - start) >> PAGE_SHIFT,
+ PAGE_KERNEL_RO);

printk(KERN_INFO "Write protecting the kernel read-only data: %luk\n",
(end - start) >> 10);
@@ -632,7 +620,43 @@
* of who is the culprit.
*/
global_flush_tlb();
+ rodata_marked = 1;
+}
+
+/*
+ * Mark kernel text pages writable.
+ */
+void 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);
+
+void 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;
+ mb();
+ change_page_attr(virt_to_page(address), nr_pages,
+ PAGE_KERNEL_RO);
+ mb();
+ global_flush_tlb();
+ }
}
+EXPORT_SYMBOL_GPL(kernel_text_unmark);
#endif

#ifdef CONFIG_BLK_DEV_INITRD
Index: linux-2.6-lttng/include/asm-x86_64/cacheflush.h
===================================================================
--- linux-2.6-lttng.orig/include/asm-x86_64/cacheflush.h 2007-07-13 16:08:14.000000000 -0400
+++ linux-2.6-lttng/include/asm-x86_64/cacheflush.h 2007-07-13 16:34:32.000000000 -0400
@@ -33,4 +33,13 @@
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 /* _X8664_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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