[PATCH] x86/x86_64: mark rodata section read only: x86 parts

x86 specific parts to make the .rodata section read only

Signed-off-by: Arjan van de Ven <arjan@infradead.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Adrian Bunk <bunk@stusta.de>
Cc: Andi Kleen <ak@muc.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

3 files changed, 38 insertions, 0 deletions

diff --git a/arch/i386/Kconfig.debug b/arch/i386/Kconfig.debug
index c48b424dd640..bf32ecc9ad04 100644
--- a/arch/i386/Kconfig.debug
+++ b/arch/i386/Kconfig.debug
@@ -42,6 +42,16 @@ config DEBUG_PAGEALLOC
           This results in a large slowdown, but helps to find certain types
           of memory corruptions.
 
+config DEBUG_RODATA
+        bool "Write protect kernel read-only data structures"
+        depends on DEBUG_KERNEL
+        help
+          Mark the kernel read-only data as write-protected in the pagetables,
+          in order to catch accidental (and incorrect) writes to such const
+          data. This option may have a slight performance impact because a
+          portion of the kernel code won't be covered by a 2MB TLB anymore.
+          If in doubt, say "N".
+
 config 4KSTACKS
         bool "Use 4Kb for kernel stacks instead of 8Kb"
         depends on DEBUG_KERNEL
diff --git a/arch/i386/mm/init.c b/arch/i386/mm/init.c
index 06e26f006238..7df494b51a5b 100644
--- a/arch/i386/mm/init.c
+++ b/arch/i386/mm/init.c
@@ -735,6 +735,30 @@ void free_initmem(void)
         printk (KERN_INFO "Freeing unused kernel memory: %dk freed\n", (__init_end - __init_begin) >> 10);
 }
 
+#ifdef CONFIG_DEBUG_RODATA
+
+extern char __start_rodata, __end_rodata;
+void mark_rodata_ro(void)
+{
+        unsigned long addr = (unsigned long)&__start_rodata;
+
+        for (; addr < (unsigned long)&__end_rodata; addr += PAGE_SIZE)
+                change_page_attr(virt_to_page(addr), 1, PAGE_KERNEL_RO);
+
+        printk ("Write protecting the kernel read-only data: %luk\n",
+                        (unsigned long)(&__end_rodata - &__start_rodata) >> 10);
+
+        /*
+         * change_page_attr() requires a global_flush_tlb() call after it.
+         * We do this after the printk so that if something went wrong in the
+         * change, the printk gets out at least to give a better debug hint
+         * of who is the culprit.
+         */
+        global_flush_tlb();
+}
+#endif
+
+
 #ifdef CONFIG_BLK_DEV_INITRD
 void free_initrd_mem(unsigned long start, unsigned long end)
 {
diff --git a/include/asm-i386/cacheflush.h b/include/asm-i386/cacheflush.h
index 2ea36dea37d9..7199f7b326f1 100644
--- a/include/asm-i386/cacheflush.h
+++ b/include/asm-i386/cacheflush.h
@@ -31,4 +31,8 @@ int change_page_attr(struct page *page, int numpages, pgprot_t prot);
 void kernel_map_pages(struct page *page, int numpages, int enable);
 #endif
 
+#ifdef CONFIG_DEBUG_RODATA
+void mark_rodata_ro(void);
+#endif
+
 #endif /* _I386_CACHEFLUSH_H */