From: Nick Piggin <npiggin@novell.com>
Subject: Add mark_rodata_rw() to un-protect read-only kernel code pages
Patch-mainline: probably never
References: bnc#439348

CONFIG_RODATA presents a problem for antivirus vendors who do not have a
clean user-space interface for getting virus scanning triggered, and
currently resort to patching the kernel code instead (presumably the
ystem call table). With CONFIG_RODATA enabled, the kernel rejects such
write accesses.

Add a new mark_rodata_rw() function to un-protect the read-only kernel code
pages for now, and export mark_rodata_ro() and mark_rodata_rw() to modules.

This is not meant as a permanent workaround, and will be removed again in the
next release!

Acked-by: Andres Gruenbacher <agruen@suse.de>

Automatically created from "patches.suse/x86-mark_rodata_rw.patch" by xen-port-patches.py

--- head-2011-03-17.orig/arch/x86/mm/init_32-xen.c	2011-02-01 15:41:35.000000000 +0100
+++ head-2011-03-17/arch/x86/mm/init_32-xen.c	2011-02-02 15:07:16.000000000 +0100
@@ -1035,5 +1035,19 @@ void mark_rodata_ro(void)
 #endif
 	mark_nxdata_nx();
 }
+EXPORT_SYMBOL_GPL(mark_rodata_ro);
+
+void mark_rodata_rw(void)
+{
+	unsigned long start = PFN_ALIGN(_text);
+	unsigned long size = PFN_ALIGN(_etext) - start;
+
+	start += size;
+	size = (unsigned long)__end_rodata - start;
+	set_pages_rw_force(virt_to_page(start), size >> PAGE_SHIFT);
+	printk(KERN_INFO "Write enabling the kernel read-only data: %luk\n",
+		size >> 10);
+}
+EXPORT_SYMBOL_GPL(mark_rodata_rw);
 #endif
 
--- head-2011-03-17.orig/arch/x86/mm/init_64-xen.c	2011-03-17 14:22:21.000000000 +0100
+++ head-2011-03-17/arch/x86/mm/init_64-xen.c	2011-02-02 15:07:16.000000000 +0100
@@ -1042,6 +1042,7 @@ void set_kernel_text_ro(void)
 	set_memory_ro(start, (end - start) >> PAGE_SHIFT);
 }
 
+static int initmem_freed __read_mostly = 0;
 void mark_rodata_ro(void)
 {
 	unsigned long start = PFN_ALIGN(_text);
@@ -1074,15 +1075,33 @@ void mark_rodata_ro(void)
 	set_memory_ro(start, (end-start) >> PAGE_SHIFT);
 #endif
 
-	free_init_pages("unused kernel memory",
-			(unsigned long) page_address(virt_to_page(text_end)),
-			(unsigned long)
+	if (!initmem_freed) {
+		initmem_freed = 1;
+		free_init_pages("unused kernel memory",
+				(unsigned long)
+				 page_address(virt_to_page(text_end)),
+				(unsigned long)
 				 page_address(virt_to_page(rodata_start)));
-	free_init_pages("unused kernel memory",
-			(unsigned long) page_address(virt_to_page(rodata_end)),
-			(unsigned long) page_address(virt_to_page(data_start)));
+		free_init_pages("unused kernel memory",
+				(unsigned long)
+				 page_address(virt_to_page(rodata_end)),
+				(unsigned long)
+				 page_address(virt_to_page(data_start)));
+	}
 }
+EXPORT_SYMBOL_GPL(mark_rodata_ro);
 
+void mark_rodata_rw(void)
+{
+	unsigned long rodata_start =
+		((unsigned long)__start_rodata + PAGE_SIZE - 1) & PAGE_MASK;
+	unsigned long end = (unsigned long) &__end_rodata;
+
+	printk(KERN_INFO "Write enabling the kernel read-only data: %luk\n",
+	       (end - rodata_start) >> 10);
+	set_memory_rw_force(rodata_start, (end - rodata_start) >> PAGE_SHIFT);
+}
+EXPORT_SYMBOL_GPL(mark_rodata_rw);
 #endif
 
 int kern_addr_valid(unsigned long addr)
--- head-2011-03-17.orig/arch/x86/mm/pageattr-xen.c	2011-03-17 14:22:21.000000000 +0100
+++ head-2011-03-17/arch/x86/mm/pageattr-xen.c	2011-03-17 14:33:38.000000000 +0100
@@ -244,6 +244,8 @@ static void cpa_flush_array(unsigned lon
 	}
 }
 
+static int static_protections_allow_rodata __read_mostly;
+
 /*
  * Certain areas of memory on x86 require very specific protection flags,
  * for example the BIOS area or kernel text. Callers don't always get this
@@ -277,8 +279,10 @@ static inline pgprot_t static_protection
 	 * catches all aliases.
 	 */
 	if (within(pfn, __pa((unsigned long)__start_rodata) >> PAGE_SHIFT,
-		   __pa((unsigned long)__end_rodata) >> PAGE_SHIFT))
-		pgprot_val(forbidden) |= _PAGE_RW;
+		   __pa((unsigned long)__end_rodata) >> PAGE_SHIFT)) {
+		if (!static_protections_allow_rodata)
+			pgprot_val(forbidden) |= _PAGE_RW;
+	}
 
 #if defined(CONFIG_X86_64) && defined(CONFIG_DEBUG_RODATA) && !defined(CONFIG_XEN)
 	/*
@@ -1216,6 +1220,21 @@ int set_memory_rw(unsigned long addr, in
 }
 EXPORT_SYMBOL_GPL(set_memory_rw);
 
+/* hack: bypass kernel rodata section static_protections check. */
+int set_memory_rw_force(unsigned long addr, int numpages)
+{
+	static DEFINE_MUTEX(lock);
+	int ret;
+
+	mutex_lock(&lock);
+	static_protections_allow_rodata = 1;
+	ret = change_page_attr_set(&addr, numpages, __pgprot(_PAGE_RW), 0);
+	static_protections_allow_rodata = 0;
+	mutex_unlock(&lock);
+
+	return ret;
+}
+
 int set_memory_np(unsigned long addr, int numpages)
 {
 	return change_page_attr_clear(&addr, numpages, __pgprot(_PAGE_PRESENT), 0);
@@ -1349,6 +1368,13 @@ int set_pages_rw(struct page *page, int 
 	return set_memory_rw(addr, numpages);
 }
 
+int set_pages_rw_force(struct page *page, int numpages)
+{
+	unsigned long addr = (unsigned long)page_address(page);
+
+	return set_memory_rw_force(addr, numpages);
+}
+
 #ifdef CONFIG_DEBUG_PAGEALLOC
 
 static int __set_pages_p(struct page *page, int numpages)
