[PARISC] Add CONFIG_DEBUG_RODATA to protect read-only data

Add the parisc version of the "mark rodata section read only" patches.
Based on code from and Signed-off-by Arjan van de Ven
<arjan@infradead.org>, Ingo Molnar <mingo@elte.hu>, Andi Kleen <ak@muc.de>,
Andrew Morton <akpm@osdl.org>, Linus Torvalds <torvalds@osdl.org>.

Signed-off-by: Helge Deller <deller@parisc-linux.org>
Signed-off-by: Kyle McMartin <kyle@parisc-linux.org>

arch/parisc/Kconfig.debug

@@ -11,4 +11,14 @@ config DEBUG_RWLOCK
           too many attempts.  If you suspect a rwlock problem or a kernel
           hacker asks for this option then say Y.  Otherwise say N.
 
+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 TLB anymore.
+         If in doubt, say "N".
+
 endmenu

arch/parisc/hpux/entry_hpux.S

@@ -22,10 +22,9 @@
 #include <linux/linkage.h>
 #include <asm/unistd.h>
 
-	.text
-
 #define ENTRY_NAME(_name_) .word _name_
 
+	.section .rodata,"a"
 	.align 4
 	.export hpux_call_table
 	.import hpux_unimplemented_wrapper

arch/parisc/kernel/syscall.S

@@ -650,6 +650,8 @@ end_linux_gateway_page:
 #define LWS_ENTRY(_name_) .word  (lws_##_name_ - linux_gateway_page)
 #endif
 
+	.section .rodata,"a"
+
 	.align 4096
 	/* Light-weight-syscall table */
 	/* Start of lws table. */

arch/parisc/mm/init.c

@@ -417,6 +417,19 @@ void free_initmem(void)
 #endif
 }
 
+
+#ifdef CONFIG_DEBUG_RODATA
+void mark_rodata_ro(void)
+{
+	extern char __start_rodata, __end_rodata;
+	/* rodata memory was already mapped with KERNEL_RO access rights by
+           pagetable_init() and map_pages(). No need to do additional stuff here */
+	printk (KERN_INFO "Write protecting the kernel read-only data: %luk\n",
+		(unsigned long)(&__end_rodata - &__start_rodata) >> 10);
+}
+#endif
+
+
 /*
  * Just an arbitrary offset to serve as a "hole" between mapping areas
  * (between top of physical memory and a potential pcxl dma mapping
@@ -685,7 +698,7 @@ static void __init pagetable_init(void)
 
 #ifdef CONFIG_BLK_DEV_INITRD
 	if (initrd_end && initrd_end > mem_limit) {
-		printk("initrd: mapping %08lx-%08lx\n", initrd_start, initrd_end);
+		printk(KERN_INFO "initrd: mapping %08lx-%08lx\n", initrd_start, initrd_end);
 		map_pages(initrd_start, __pa(initrd_start),
 			initrd_end - initrd_start, PAGE_KERNEL);
 	}

include/asm-parisc/cacheflush.h

@@ -183,4 +183,10 @@ flush_cache_page(struct vm_area_struct *vma, unsigned long vmaddr, unsigned long
 		__flush_cache_page(vma, vmaddr);
 
 }
+
+#ifdef CONFIG_DEBUG_RODATA
+void mark_rodata_ro(void);
 #endif
+
+#endif /* _PARISC_CACHEFLUSH_H */
+

include/asm-parisc/pgtable.h

@@ -213,7 +213,7 @@ extern  void *vmalloc_start;
 #define PAGE_COPY       PAGE_EXECREAD
 #define PAGE_RWX        __pgprot(_PAGE_PRESENT | _PAGE_USER | _PAGE_READ | _PAGE_WRITE | _PAGE_EXEC |_PAGE_ACCESSED)
 #define PAGE_KERNEL	__pgprot(_PAGE_KERNEL)
-#define PAGE_KERNEL_RO	__pgprot(_PAGE_PRESENT | _PAGE_EXEC | _PAGE_READ | _PAGE_DIRTY | _PAGE_ACCESSED)
+#define PAGE_KERNEL_RO	__pgprot(_PAGE_KERNEL & ~_PAGE_WRITE)
 #define PAGE_KERNEL_UNC	__pgprot(_PAGE_KERNEL | _PAGE_NO_CACHE)
 #define PAGE_GATEWAY    __pgprot(_PAGE_PRESENT | _PAGE_USER | _PAGE_ACCESSED | _PAGE_GATEWAY| _PAGE_READ)
 #define PAGE_FLUSH      __pgprot(_PAGE_FLUSH)